xref: /docs/en/application-dev/ui/state-management/arkts-new-persistencev2.md

# PersistenceV2: Persisting Application State

To enhance the state management framework's capability of persistently storing UIs, you can use **PersistenceV2** to persist data.

**PersistenceV2** is an optional singleton object within an application. Its purpose is to persist UI-related data so that their values are the same upon application re-start as they were when the application was closed.

**PersistenceV2** provides the state variable persistence capability. You can bind the same key through **connect** or **globalConnect** to implement the persistence capability during state variable change and application cold start.

Before reading this topic, you are advised to read [\@ComponentV2](./arkts-new-componentV2.md), [\@ObservedV2 and \@Trace](./arkts-new-observedV2-and-trace.md), and API reference of [PersistentV2](../../reference/apis-arkui/js-apis-StateManagement.md#persistencev2).

>**NOTE**
>
>**PersistenceV2** is supported since API version 12.
>
>**globalConnect** is supported since API version 18. The behavior of **globalConnect** is the same as that of **connect**. The only difference is that the underlying storage path of **connect** is a module-level path, while that of **globalConnect** is an application-level path. For details, see the section [Using connect and globalConnect in Different Modules](#using-connect-and-globalconnect-in-different-modules).


## Overview

**PersistenceV2** is a singleton to be created when the application UI is started. Its purpose is to provide central storage for application UI state attributes. Each attribute is accessed using a unique key, which is a string. Unlike **AppStorageV2**, **PersistenceV2** also persistently stores the latest data on device disks. In this way, the selected result can still be saved even when the application is closed.

For a [\@ObservedV2](./arkts-new-observedV2-and-trace.md) object associated with **PersistenceV2**, the change of the [\@Trace](./arkts-new-observedV2-and-trace.md) attribute of the object triggers automatic persistence of the entire associated object. If necessary, you can call **PersistenceV2** APIs to manually perform persistence.

**PersistenceV2** can synchronize application state attributes with UI components and can be accessed during implementation of application service logic as well.

**PersistenceV2** supports state sharing among multiple UIAbility instances in the [main thread](../../application-models/thread-model-stage.md) of an application.

## How to Use

### connect: Creating or Obtaining Stored Data

```JavaScript
static connect<T extends object>(
    type: TypeConstructorWithArgs<T>,
    keyOrDefaultCreator?: string | StorageDefaultCreator<T>,
    defaultCreator?: StorageDefaultCreator<T>
): T | undefined;
```

| connect      | Description                                                 |
| ------------ | ----------------------------------------------------- |
| Parameter        | **type**: specified type. If no **key** is specified, the name of the **type** is used as the **key**.<br> **keyOrDefaultCreator**: specified key or default constructor.<br> **defaultCreator**: default constructor.                                         |
| Return value      | After creating or obtaining data, value is returned. Otherwise, **undefined** is returned.|

>**NOTE**
>
>1. The second parameter is used when no **key** is specified or the second parameter is invalid, and the third parameter is used in all other cases.
>
>2. If the data has been stored in **PersistenceV2**, you can obtain the stored data without using the default constructor. Otherwise, you must specify the default constructor. If no constructor is specified, the application exception occurs.
>
>3. Ensure that the data types match the key. Connecting different types of data to the same key will result in an application exception.
>
>4. You are advised to use meaningful values for keys. The values can contain letters, digits, and underscores (_) and a maximum of 255 characters. Using invalid characters or null characters will result in undefined behavior.
>
>5. When matching the key with the [\@Observed](./arkts-observed-and-objectlink.md) object, specify the key or customize the **name** attribute.
>
>6. The data storage path is at the module level. That is, the data copy is stored in the persistent file of the corresponding module when the module calls the **connect** function. If multiple modules use the same key, the data of the module that uses the **connect** function first is used, and the data in **PersistenceV2** is also stored in the module that uses the **connect** function first.
>
>7. The storage path, determined when the first ability of the application is started, is the module to which the ability belongs. If an ability calls the **connect** function and can be started by different modules, the number of data copies is the same as the number of startup modes of the ability.

### globalConnect: Creating or Obtaining Stored Data

```ts
// globalConnect API
static globalConnect<T extends object>(
    type: ConnectOptions<T>
  ): T | undefined;
```

```ts
// ConnectOptions parameters
class ConnectOptions<T extends object> {
  type: TypeConstructorWithArgs<T>;	// (Mandatory) Specified type.
  key?: string;	// (Optional) Input key. If no key is specified, the name of the type is used as the key.
  defaultCreator?: StorageDefaultCreator<T> // Default constructor. You are advised to set this parameter.
  areaMode?: contextConstant.AreaMode; // (Optional) Encryption parameter.
}
```

| globalConnect | Description                                                     |
| ------------- | --------------------------------------------------------- |
| Parameter         | type: input parameter of **connect**. For details, see the description of **ConnectOptions**.|
| Return value       | After creating or obtaining data, value is returned. Otherwise, **undefined** is returned.      |

| ConnectOptions| Description                                                        |
| :----------------: | :----------------------------------------------------------- |
|        type        | **TypeConstructorWithArgs\<T\>**: (mandatory) specified type.        |
|        key         | Input key of the string type. If no value is passed in, the type name is used as the key.            |
|   defaultCreator   | **StorageDefaultCreator\<T\>**: default constructor. It is recommended that this parameter be passed in. If **globalConnect** is connected to the key for the first time, an error is reported if no parameter is passed in.|
|      areaMode      | **contextConstant.AreaMode**: encryption level, ranging from EL1 to EL5 (corresponding to the value from 0 to 4). For details, see [Encryption Levels](../../application-models/application-context-stage.md#obtaining-and-modifying-encryption-levels). If no value is passed in, EL2 is used by default. Storage paths vary based on the encryption levels. If the input value of encryption level is not in the range of **0** to **4**, a crash occurs.|

> **NOTE**
>
> 1. The second parameter is used when no **key** is specified or the second parameter is invalid, and the third parameter is used in all other cases.
>
> 2. If the data has been stored in **PersistenceV2**, you can obtain the stored data without using the default constructor. Otherwise, you must specify the default constructor. If no constructor is specified, the application exception occurs.
>
> 3. Ensure that the data types match the key. Matching different types of **globalConnect** data to the same key will result in an application exception.
>
> 4. You are advised to use meaningful values for keys. The values can contain letters, digits, and underscores (_) and a maximum of 255 characters. Using invalid characters or null characters will result in undefined behavior.
>
> 5. When matching the key with the [\@Observed](./arkts-observed-and-objectlink.md) object, specify the key or customize the **name** attribute.
>
> 6. Data is stored in an application-level path. Different modules use the same key and encryption level for **globalConnect**. Only one copy of data is stored.
>
> 7. **globalConnect** uses the same key but sets different encryption levels, in which the first-set encryption level is used. Data in **PersistenceV2** is also stored at the encryption level that uses the key first.
>
> 8. You are not advised to use **connect** and **globalConnect** together because the data copy paths are different. If they are used together, the keys must be different; otherwise, a crash occurs.
>
> 9. To make EL5 encryption level take effect, you need to configure the **ohos.permission.PROTECT_SCREEN_LOCK_DATA** field in the **module.json** file. For details, see [Declaring Permissions](../../security/AccessToken/declare-permissions.md).

### remove: Deleting the Stored Data of a Specified Key

```ts
static remove<T>(keyOrType: string | TypeConstructorWithArgs<T>): void;
```

| remove       | Description                                                 |
| ------------ | ----------------------------------------------------- |
| Parameter        | **keyOrType**: key to be deleted. If the key is of the **type**, the key to be deleted is the name of the **type**.                                         |
| Return value      | None.|

>**NOTE**
>
>If a key that does not exist in **PersistenceV2** is deleted, a warning is reported.

### keys: Returning All Keys Stored in PersistenceV2

```ts
static keys(): Array<string>;
```

| keys         | Description                                                 |
| ------------ | ----------------------------------------------------- |
| Parameter        | None.                                        |
| Return value      | All keys in **PersistenceV2**.|

> **NOTE**
>
> All keys in the module-level and application-level storage paths are returned.

### save: Persisting Stored Data Manually

```ts
static save<T>(keyOrType: string | TypeConstructorWithArgs<T>): void;
```

| save         | Description                                                 |
| ------------ | ----------------------------------------------------- |
| Parameter        | **keyOrType**: key that needs to be manually persist. If the key is of the **Type**, the key is the name of the **Type**.                                         |
| Return value      | None.|

>**NOTE**
>
>Changes to the non-[\@Trace](./arkts-new-observedV2-and-trace.md) data do not trigger **PersistenceV2**. If necessary, call this API to persist the data of the corresponding key.
>
>It is useless to manually persist the keys that are not in the **connect** state in the memory.


### **notifyOnError**: Callback for Responding to a Serialization or Deserialization Failure

```ts
static notifyOnError(callback: PersistenceErrorCallback | undefined): void;
```

| notifyOnError| Description                                                 |
| ------------ | ----------------------------------------------------- |
| Parameter        | **callback**: When a serialization or deserialization fails, the callback is executed. Pass in **undefined** can cancel this callback.|
| Return value      | None.|

>**NOTE**
>
>When data is stored to disks, the data needs to be serialized. If a key fails to be serialized, the error is unpredictable. As a result, this API can be called to capture exceptions.


## Constraints

1. This singleton must be used together with the UI thread only. Other threads, for example, @Sendable decorator is not supported.

2. Types such as **collections.Set** and **collections.Map** are not supported.

3. Non-buildin types, such as native PixelMap, NativePointer, and ArrayList types, are not supported.

4. A single key supports a maximum of 8 KB data. If the data is too large, the persistence fails.

5. The persistent data must be a class object. Containers, such as Array, Set, and Map, or objects of the built-in types, such as Date and Number, are not supported.

6. Objects that used for loop reference are not supported.

7. Automatic persistency is triggered only when [\@Trace](./arkts-new-observedV2-and-trace.md) data is changed. The change of state variables in V1, [\@Observed](./arkts-observed-and-objectlink.md) objects, and common data does not trigger persistency.

8. Do not store a large amount of persistent data. Otherwise, frame freezing may occur.

9. Do not use **connect** and **globalConnect** together. If you have to, their keys must be different; otherwise, a crash occurs.

## Use Scenarios

### Storing Data Between Two Pages

Data page
```ts
// Sample.ets
import { Type } from '@kit.ArkUI';

// Data center
@ObservedV2
class SampleChild {
  @Trace p1: number = 0;
  p2: number = 10;
}

@ObservedV2
export class Sample {
  // Complex objects need to be decorated by @Type to ensure successful serialization.
  @Type(SampleChild)
  @Trace f: SampleChild = new SampleChild();
}
```

Page 1
```ts
// Page1.ets
import { PersistenceV2 } from '@kit.ArkUI';
import { Sample } from '../Sample';

// Callback used to receive serialization failure.
PersistenceV2.notifyOnError((key: string, reason: string, msg: string) => {
  console.error(`error key: ${key}, reason: ${reason}, message: ${msg}`);
});

@Entry
@ComponentV2
struct Page1 {
  // Create a KV pair whose key is Sample in PersistenceV2 (if the key exists, the data in PersistenceV2 is returned) and associate it with prop.
  // Add @Local to decorate the prop attribute that needs to change the connected object. (Changing the connected object is not recommended.)
  @Local prop: Sample = PersistenceV2.connect(Sample, () => new Sample())!;
  pageStack: NavPathStack = new NavPathStack();

  build() {
    Navigation(this.pageStack) {
      Column() {
        Button('Go to page2')
          .onClick(() => {
            this.pageStack.pushPathByName('Page2', null);
          })

        Button('Page1 connect the key Sample')
          .onClick(() => {
            // Create a KV pair whose key is Sample in PersistenceV2 (if the key exists, the data in PersistenceV2 is returned) and associate it with prop.
            // Changing the connected object for the prop attribute is not recommended.
            this.prop = PersistenceV2.connect(Sample, 'Sample', () => new Sample())!;
          })

        Button('Page1 remove the key Sample')
          .onClick(() => {
            // After being deleted from PersistenceV2, prop will no longer be associated with the value whose key is Sample.
            PersistenceV2.remove(Sample);
          })

        Button('Page1 save the key Sample')
          .onClick(() => {
            // If the sample is in the connect state, persist the KV pair of the Sample.
            PersistenceV2.save(Sample);
          })

        Text(`Page1 add 1 to prop.p1: ${this.prop.f.p1}`)
          .fontSize(30)
          .onClick(() => {
            this.prop.f.p1++;
          })

        Text(`Page1 add 1 to prop.p2: ${this.prop.f.p2}`)
          .fontSize(30)
          .onClick(() => {
            // The page is not re-rendered, but the value of p2 is changed.
            this.prop.f.p2++;
          })

        // Obtain all keys in the current PersistenceV2.
        Text(`all keys in PersistenceV2: ${PersistenceV2.keys()}`)
          .fontSize(30)
      }
      }
  }
}
```

Page 2
```ts
// Page2.ets
import { PersistenceV2 } from '@kit.ArkUI';
import { Sample } from '../Sample';

@Builder
export function Page2Builder() {
  Page2()
}

@ComponentV2
struct Page2 {
  // Create a KV pair whose key is Sample in PersistenceV2 (if the key exists, the data in PersistenceV2 is returned) and associate it with prop.
  // Add @Local to decorate the prop attribute that needs to change the connected object. (Changing the connected object is not recommended.)
  @Local prop: Sample = PersistenceV2.connect(Sample, () => new Sample())!;
  pathStack: NavPathStack = new NavPathStack();

  build() {
    NavDestination() {
      Column() {
        Button('Page2 connect the key Sample1')
          .onClick(() => {
            // Create a KV pair whose key is Sample1 in PersistenceV2 (if the key exists, the data in PersistenceV2 is returned) and associate it with prop.
            // Changing the connected object for the prop attribute is not recommended.
            this.prop = PersistenceV2.connect(Sample, 'Sample1', () => new Sample())!;
          })

        Text(`Page2 add 1 to prop.p1: ${this.prop.f.p1}`)
          .fontSize(30)
          .onClick(() => {
            this.prop.f.p1++;
          })

        Text(`Page2 add 1 to prop.p2: ${this.prop.f.p2}`)
          .fontSize(30)
          .onClick(() => {
            // The page is not re-rendered, but the value of p2 is changed, which is performed after re-initialization.
            this.prop.f.p2++;
          })

        // Obtain all keys in the current PersistenceV2.
        Text(`all keys in PersistenceV2: ${PersistenceV2.keys()}`)
          .fontSize(30)
      }
    }
    .onReady((context: NavDestinationContext) => {
      this.pathStack = context.pathStack;
    })
  }
}
```
When using **Navigation**, you need to add the **route_map.json** file to the **src/main/resources/base/profile** directory, replace the value of **pageSourceFile** with the path of **Page2**, and add **"routerMap": "$profile: route_map"** to the **module.json5** file.
```json
{
  "routerMap": [
    {
      "name": "Page2",
      "pageSourceFile": "src/main/ets/pages/Page2.ets",
      "buildFunction": "Page2Builder",
      "data": {
        "description" : "PersistenceV2 example"
      }
    }
  ]
}
```

### Using globalConnect to Store Data

```ts
import { PersistenceV2, Type, ConnectOptions } from '@kit.ArkUI';
import { contextConstant } from '@kit.AbilityKit';

// Callback used to receive serialization failure.
PersistenceV2.notifyOnError((key: string, reason: string, msg: string) => {
  console.error(`error key: ${key}, reason: ${reason}, message: ${msg}`);
});

@ObservedV2
class SampleChild {
  @Trace childId: number = 0;
  groupId: number = 1;
}

@ObservedV2
export class Sample {
  // Complex objects need to be decorated by @Type to ensure successful serialization.
  @Type(SampleChild)
  @Trace father: SampleChild = new SampleChild();
}

@Entry
@ComponentV2
struct Page1 {
  @Local refresh: number = 0;
  // Use the type name as the key if no key is passed in; use EL2 as the default encryption level if no encryption parameter is passed in.
  @Local p: Sample = PersistenceV2.globalConnect({type: Sample, defaultCreator:() => new Sample()})!;

  // Use key:global1 for connection and set the encryption level to EL1.
  @Local p1: Sample = PersistenceV2.globalConnect({type: Sample, key:'global1', defaultCreator:() => new Sample(), areaMode: contextConstant.AreaMode.EL1})!;

  // Use key:global2 for connection and use the constructor function. If no encryption parameter is passed in, EL2 is used by default.
  options: ConnectOptions<Sample> = {type: Sample, key: 'global2', defaultCreator:() => new Sample()};
  @Local p2: Sample = PersistenceV2.globalConnect(this.options)!;

  // Use key:global3 for connection and set the encryption parameter ranging from 0 to 4; otherwise, a crash occurs. In this case, EL3 is set.
  @Local p3: Sample = PersistenceV2.globalConnect({type: Sample, key:'global3', defaultCreator:() => new Sample(), areaMode: 3})!;

  build() {
    Column() {
      /**************************** Display data **************************/
      // Data decorated by @Trace can be automatically persisted to disks.
      Text('Key Sample: ' + this.p.father.childId.toString())
        .onClick(()=> {
          this.p.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)
      Text('Key global1: ' + this.p1.father.childId.toString())
        .onClick(()=> {
          this.p1.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)
      Text('Key global2: ' + this.p2.father.childId.toString())
        .onClick(()=> {
          this.p2.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)
      Text('Key global3: ' + this.p3.father.childId.toString())
        .onClick(()=> {
          this.p3.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)
      /**************************** The keys API **************************/
      // keys() is not updated by itself. You need to use the state variable to update it.
      Text('Persist keys: ' + PersistenceV2.keys().toString() + ' refresh: ' + this.refresh)
        .onClick(() => {
          this.refresh += 1;
        })
        .fontSize(25)

      /**************************** The remove API **************************/
      Text('Remove key Sample: ' + 'refresh: ' + this.refresh)
        .onClick(() => {
          // Removing this key will disconnect from PersistenceV2. After that, PersistenceV2 cannot store data even if it is reconnected.
          PersistenceV2.remove(Sample);
          this.refresh += 1;
        })
        .fontSize(25)
      Text('Remove key global1: ' + 'refresh: ' + this.refresh)
        .onClick(() => {
          // Removing this key will disconnect from PersistenceV2. After that, PersistenceV2 cannot store data even if it is reconnected.
          PersistenceV2.remove('global1');
          this.refresh += 1;
        })
        .fontSize(25)
      Text('Remove key global2: ' + 'refresh: ' + this.refresh)
        .onClick(() => {
          // Removing this key will disconnect from PersistenceV2. After that, PersistenceV2 cannot store data even if it is reconnected.
          PersistenceV2.remove('global2');
          this.refresh += 1;
        })
        .fontSize(25)
      Text('Remove key global3: ' + 'refresh: ' + this.refresh)
        .onClick(() => {
          // Removing this key will disconnect from PersistenceV2. After that, PersistenceV2 cannot store data even if it is reconnected.
          PersistenceV2.remove('global3');
          this.refresh += 1;
        })
        .fontSize(25)
      /**************************** reConnect **************************/
      // Fail to connect to the previous state variable after reconnection. Therefore, data cannot be saved.
      Text('ReConnect key global2: ' + 'refresh: ' + this.refresh)
        .onClick(() => {
          // Removing this key will disconnect from PersistenceV2. After that, PersistenceV2 cannot store data even if it is reconnected.
          PersistenceV2.globalConnect(this.options);
          this.refresh += 1;
        })
        .fontSize(25)

      /**************************** The save API **************************/
      Text('not save key Sample: ' + this.p.father.groupId.toString() + ' refresh: ' + this.refresh)
        .onClick(() => {
          // Objects that are not saved by @Trace cannot be automatically stored.
          this.p.father.groupId += 1;
          this.refresh += 1;
        })
        .fontSize(25)
      Text('save key Sample: ' + this.p.father.groupId.toString() + ' refresh: ' + this.refresh)
        .onClick(() => {
          // Objects that are not saved by @Trace cannot be automatically stored. You need to call the key for storage.
          this.p.father.groupId += 1;
          PersistenceV2.save(Sample);
          this.refresh += 1;
        })
        .fontSize(25)
    }
    .width('100%')
  }
}
```

### Using connect and globalConnect in Different Modules

**For the storage path of connect:**

1. **connect** uses the first-started module path as the storage path and data is written back from the memory to this storage path in the disk. If the application is started from another module, the path of the new module is used as the storage path.

2. When different modules use the same key, the key-value pair stored in the module that is started first is written back to the corresponding module.

**For the storage path of GlobalConnect:**

Although **globalConnect** is an application-level path, different encryption levels can be set, indicating different storage paths. **connect** does not support the setting of the encryption level. However, when the encryption level of the module is switched, the module storage path is also switched to the path of the corresponding encryption level.

Create a module based on the project and redirect to the new module based on the sample code. The sample code is as follows:

```ts
// Module 1
import { PersistenceV2, Type } from '@kit.ArkUI';
import { contextConstant, common, Want } from '@kit.AbilityKit';

// Callback used to receive serialization failure.
PersistenceV2.notifyOnError((key: string, reason: string, msg: string) => {
  console.error(`error key: ${key}, reason: ${reason}, message: ${msg}`);
});

@ObservedV2
class SampleChild {
  @Trace childId: number = 0;
  groupId: number = 1;
}

@ObservedV2
export class Sample {
  // Complex objects need to be decorated by @Type to ensure successful serialization.
  @Type(SampleChild)
  @Trace father: SampleChild = new SampleChild();
}

@Entry
@ComponentV2
struct Page1 {
  @Local refresh: number = 0;
  // Use key:global1 for connection and set the encryption level to EL1.
  @Local p1: Sample = PersistenceV2.globalConnect({type: Sample, key:'globalConnect1', defaultCreator:() => new Sample()})!;

  // Use key:global2 for connection and use the constructor function. If no encryption parameter is passed in, EL2 is used by default.
  @Local p2: Sample = PersistenceV2.connect(Sample, 'connect2', () => new Sample())!;

  private context = getContext(this) as common.UIAbilityContext;

  build() {
    Column() {
      /**************************** Display data **************************/
      Text('Key globalConnect1: ' + this.p1.father.childId.toString())
        .onClick(()=> {
          this.p1.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)
      Text('Key connect2: ' + this.p2.father.childId.toString())
        .onClick(()=> {
          this.p2.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)

      /**************************** Redirection **************************/
      Button('Redirect to newModule').onClick(() => { // Used between different modules. You are advised to use globalConnect.
        let want: Want = {
          deviceId: '', // If deviceId is empty, the device is the local device.
          bundleName: 'com.example.myPersistenceV2', // Check it in app.json5.
          moduleName: 'newModule', // Check this optional value in the module.json5 file of the module to be redirected to.
          abilityName: 'NewModuleAbility',  // Redirect to the ability to start. You can check the ability name in the ability.ets file of the target module.
          uri:'src/main/ets/pages/Index'
        }
        // context is the UIAbilityContext of the initiator UIAbility.
        this.context.startAbility(want).then(() => {
          console.info('start ability success');
        }).catch((err: Error) => {
          console.error(`start ability failed. code is ${err.name}, message is ${err.message}`);
        })
      })
    }
    .width('100%')
    .borderWidth(3)
    .borderColor(Color.Blue)
    .margin({top: 5, bottom: 5})
  }
}
```

```ts
// Module 2
import { PersistenceV2, Type } from '@kit.ArkUI';
import { contextConstant } from '@kit.AbilityKit';

// Callback used to receive serialization failure.
PersistenceV2.notifyOnError((key: string, reason: string, msg: string) => {
  console.error(`error key: ${key}, reason: ${reason}, message: ${msg}`);
});

@ObservedV2
class SampleChild {
  @Trace childId: number = 0;
  groupId: number = 1;
}

@ObservedV2
export class Sample {
  // Complex objects need to be decorated by @Type to ensure successful serialization.
  @Type(SampleChild)
  @Trace father: SampleChild = new SampleChild();
}

@Entry
@ComponentV2
struct Page1 {
  @Local a: number = 0;
  // Use key:global1 for connection and set the encryption level to EL1.
  @Local p1: Sample = PersistenceV2.globalConnect({type: Sample, key:'globalConnect1', defaultCreator:() => new Sample()})!;

  // Use key:global2 for connection and use the constructor function. If no encryption parameter is passed in, EL2 is used by default.
  @Local p2: Sample = PersistenceV2.connect(Sample, 'connect2', () => new Sample())!;

  build() {
    Column() {
      /**************************** Display data **************************/
      Text('Key globalConnect1: ' + this.p1.father.childId.toString())
        .onClick(()=> {
          this.p1.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)
      Text('Key connect2: ' + this.p2.father.childId.toString())
        .onClick(()=> {
          this.p2.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)
    }
    .width('100%')
  }
}
```

When you use different startup modes for newModule, the following symptoms may occur:

*   Start the **newModule** and change the variables bound to **globalConnect1** and **connect2**. For example, change the value of **childId** to **5**.
* Exit the application, clear the background, start the module entry, and start **newModule** by pressing the redirection key. The value of **globalConnect1** is **5**, and the value of **connect2** remains **1**.
* **globalConnect** is an application-level storage path. For a key, the entire application has only one storage path for the corresponding encryption level. **connect** is a module-level storage path. Each encryption level has a different storage path according to the startup mode of the module.

## Suggestions

You are advised to use the new API **globalConnect** to create and obtain data. The storage specifications and memory specifications of **globalConnect** are the same for an application, and the encryption level can be set without switching the encryption mode of ability. If your application does not involve multiple modules, using **connect** will not affect your application.

### Migrating from connect to globalConnect

```ts
// Use connect to store data.
import { PersistenceV2, Type } from '@kit.ArkUI';

// Callback used to receive serialization failure.
PersistenceV2.notifyOnError((key: string, reason: string, msg: string) => {
  console.error(`error key: ${key}, reason: ${reason}, message: ${msg}`);
});

@ObservedV2
class SampleChild {
  @Trace childId: number = 0;
  groupId: number = 1;
}

@ObservedV2
export class Sample {
  // Complex objects need to be decorated by @Type to ensure successful serialization.
  @Type(SampleChild)
  @Trace father: SampleChild = new SampleChild();
}

@Entry
@ComponentV2
struct Page1 {
  @Local refresh: number = 0;
  // Use key:connect2 to store data.
  @Local p: Sample = PersistenceV2.connect(Sample, 'connect2', () => new Sample())!;

  build() {
    Column({space: 5}) {
      /**************************** Display data **************************/
      Text('Key connect2: ' + this.p.father.childId.toString())
        .onClick(() => {
          this.p.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)

      /**************************** The save API **************************/
      // Non-state variables can be refreshed only by using the state variable refresh.
      Text('save key Sample: ' + this.p.father.groupId.toString() + ' refresh:' + this.refresh)
        .onClick(() => {
          // Objects that are not saved by @Trace cannot be automatically stored. You need to call the key for storage.
          this.p.father.groupId += 1;
          PersistenceV2.save('connect2');
          this.refresh += 1
        })
        .fontSize(25)
    }
    .width('100%')
  }
}
```

```ts
// Migrate to GlobalConnect.
import { PersistenceV2, Type } from '@kit.ArkUI';

// Callback used to receive serialization failure.
PersistenceV2.notifyOnError((key: string, reason: string, msg: string) => {
  console.error(`error key: ${key}, reason: ${reason}, message: ${msg}`);
});

@ObservedV2
class SampleChild {
  @Trace childId: number = 0;
  groupId: number = 1;
}

@ObservedV2
export class Sample {
  // Complex objects need to be decorated by @Type to ensure successful serialization.
  @Type(SampleChild)
  @Trace father: SampleChild = new SampleChild();
}

// Auxiliary data used to determine whether data migration is complete
@ObservedV2
class StorageState {
  @Trace isCompleteMoving: boolean = false;
}

function move() {
  let movingState = PersistenceV2.globalConnect({type: StorageState, defaultCreator: () => new StorageState()})!;
  if (!movingState.isCompleteMoving) {
    let p: Sample = PersistenceV2.connect(Sample, 'connect2', () => new Sample())!;
    PersistenceV2.remove('connect2');
    let p1 = PersistenceV2.globalConnect({type: Sample, key: 'connect2', defaultCreator: () = > p})!; // You can use the default constructor.
    // For assigned value decorated by @Trace, it is automatically saved.
    p1.father = p.father;
    // Set the migration flag to true.
    movingState.isCompleteMoving = true;
  }
}

move();

@Entry
@ComponentV2
struct Page1 {
  @Local refresh: number = 0;
  // Use key:connect2 to store data.
  @Local p: Sample = PersistenceV2.globalConnect({type: Sample, key:'connect2', defaultCreator:() => new Sample()})!;

  build() {
    Column({space: 5}) {
      /**************************** Display data **************************/
      Text('Key connect2: ' + this.p.father.childId.toString())
        .onClick(() => {
          this.p.father.childId += 1;
        })
        .fontSize(25)
        .fontColor(Color.Red)

      /**************************** The save API **************************/
      // Non-state variables can be refreshed only by using the state variable refresh.
      Text('save key connect2: ' + this.p.father.groupId.toString() + ' refresh:' + this.refresh)
        .onClick(() => {
          // Objects that are not saved by @Trace cannot be automatically stored. You need to call the key for storage.
          this.p.father.groupId += 1;
          PersistenceV2.save('connect2');
          this.refresh += 1
        })
        .fontSize(25)
    }
    .width('100%')
  }
}
```

To migrate data from **connect** to **globalConnect**, you should assign the value bound to the key to **globalConnect** for storage. When the custom component uses **globalConnect** for connection, the data bound to **globalConnect** is the data saved using **connect**. You can customize the **move** function and move the data to a proper position.