# 自定义组件成员属性访问限定符使用限制
<!--Kit: ArkUI-->
<!--Subsystem: ArkUI-->
<!--Owner: @BlYynNe-->
<!--Designer: @lixingchi1-->
<!--Tester: @TerryTsao-->
<!--Adviser: @zhang_yixin13-->

在状态管理V1版本中，完成自定义组件封装后，调用方难以明确知晓应传入哪些变量作为组件的输入参数。当组件开发者不希望状态变量被外部初始化时，可以使用private限定符来限制当前变量不允许被进行外部初始化。外部初始化也需要遵循装饰器自身的规则，具体规则见[使用限制](#使用限制)。

ArkTS会对自定义组件的成员变量使用的访问限定符private/public/protected进行校验，当不按规范使用访问限定符private/public/protected时，会产生对应的日志信息。

在阅读本文档前，建议提前阅读：[状态管理概述](./arkts-state-management-overview.md)。

> **说明：**
>
> 从API version 12开始，支持自定义组件成员属性访问限定符使用限制的规则。

## 使用限制

- [\@State](./arkts-state.md)/[\@Prop](./arkts-prop.md)/[\@Provide](./arkts-provide-and-consume.md)/[\@BuilderParam](./arkts-builderparam.md)/常规成员变量(不涉及更新的普通变量)的初始化规则为可以被外部初始化，也可以使用本地值进行初始化。当组件开发者不希望当前变量被外部初始化时，可以使用private进行修饰，在这种情况下，错误进行外部初始化会有编译告警日志提示。

- [\@StorageLink](./arkts-appstorage.md#storagelink)/[\@StorageProp](./arkts-appstorage.md#storageprop)/[\@LocalStorageLink](./arkts-localstorage.md#localstoragelink)/[\@LocalStorageProp](./arkts-localstorage.md#localstorageprop)/[\@Consume](./arkts-provide-and-consume.md)变量的初始化规则为不可以被外部初始化，当组件开发者希望当前变量被外部初始化而使用public修饰时，与装饰器本身的初始化规则不符，会有编译告警日志提示。

- [\@Link](./arkts-link.md)/[\@ObjectLink](./arkts-observed-and-objectlink.md)变量的初始化规则为必须被外部初始化，禁止本地初始化。当组件开发者使用private对变量进行修饰时，与装饰器本身的初始化规则不符，会有编译告警日志提示。

- 由于struct没有继承能力，上述所有的这些变量使用protected修饰时，会有编译告警日志提示。

- [\@Require](./arkts-require.md)含义是当前被\@Require装饰的变量必须被外部初始化，当\@Require和private同时装饰[\@State](./arkts-state.md)/[\@Prop](./arkts-prop.md)/[\@Provide](./arkts-provide-and-consume.md)/[\@BuilderParam](./arkts-builderparam.md)/常规成员变量(不涉及更新的普通变量)时，他们的含义是自相矛盾的，会有编译告警日志提示。

## 使用场景

1. 当成员变量被private访问限定符和\@State/\@Prop/\@Provide/\@BuilderParam装饰器同时修饰，并且通过父组件进行初始化赋值，ArkTS会进行校验并产生告警日志。

    【反例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      @Builder
      buildTest() {
        Text('Parent builder')
      }
    
      build() {
        Column() {
          ComponentsChild({
            state_value: 'Hello',
            prop_value: 'Hello',
            provide_value: 'Hello',
            builder_value: this.buildTest,
            regular_value: 'Hello'
          })
        }
        .width('100%')
      }
    }

    @Component
    struct ComponentsChild {
      // 此处使用private修饰符时会出现告警日志
      @State private state_value: string = 'Hello';
      // 此处使用private修饰符时会出现告警日志
      @Prop private prop_value: string = 'Hello';
      // 此处使用private修饰符时会出现告警日志
      @Provide private provide_value: string = 'Hello';
      // 此处使用private修饰符时会出现告警日志
      @BuilderParam private builder_value: () => void = this.buildTest;
      // 此处使用private修饰符时会出现告警日志
      private regular_value: string = 'Hello';
    
      @Builder
      buildTest() {
        Text('Child builder')
      }
    
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

    编译告警日志如下：

    ```ts
    Property 'state_value' is private and can not be initialized through the component constructor.
    Property 'prop_value' is private and can not be initialized through the component constructor.
    Property 'provide_value' is private and can not be initialized through the component constructor.
    Property 'builder_value' is private and can not be initialized through the component constructor.
    Property 'regular_value' is private and can not be initialized through the component constructor.
    ```

    【正例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      @Builder
      buildTest() {
        Text('Parent builder')
      }
    
      build() {
        Column() {
          ComponentsChild({
            state_value: 'Hello',
            prop_value: 'Hello',
            provide_value: 'Hello',
            builder_value: this.buildTest,
            regular_value: 'Hello'
          })
        }
        .width('100%')
      }
    }

    @Component
    struct ComponentsChild {
      @State state_value: string = 'Hello';
      @Prop prop_value: string = 'Hello';
      @Provide provide_value: string = 'Hello';
      @BuilderParam builder_value: () => void = this.buildTest;
      regular_value: string = 'Hello';
    
      @Builder
      buildTest() {
        Text('Child builder')
      }
    
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

2. 当成员变量被public访问限定符和\@StorageLink/\@StorageProp/\@LocalStorageLink/\@LocalStorageProp/\@Consume装饰器同时修饰，并且通过父组件进行初始化赋值，ArkTS会进行校验并产生告警日志。

    【反例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      @Provide consume_value: string = 'Hello';
      build() {
        Column() {
          ComponentChild()
        }
        .width('100%')
      }
    }

    @Component
    struct ComponentChild {
      // 此处使用public修饰符时会出现告警日志
      @LocalStorageProp('sessionLocalProp') public local_prop_value: string = 'Hello';
      // 此处使用public修饰符时会出现告警日志
      @LocalStorageLink('sessionLocalLink') public local_link_value: string = 'Hello';
      // 此处使用public修饰符时会出现告警日志
      @StorageProp('sessionProp') public storage_prop_value: string = 'Hello';
      // 此处使用public修饰符时会出现告警日志
      @StorageLink('sessionLink') public storage_link_value: string = 'Hello';
      // 此处使用public修饰符时会出现告警日志
      @Consume public consume_value: string;
      
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

    编译告警日志如下：

    ```ts
    Property 'local_prop_value' can not be decorated with both '@LocalStorageProp' and public.
    Property 'local_link_value' can not be decorated with both '@LocalStorageLink' and public.
    Property 'storage_prop_value' can not be decorated with both '@StorageProp' and public.
    Property 'storage_link_value' can not be decorated with both '@StorageLink' and public.
    Property 'consume_value' can not be decorated with both '@Consume' and public.
    ```
    
    【正例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      @Provide consume_value: string = 'Hello';
      build() {
        Column() {
          ComponentChild()
        }
        .width('100%')
      }
    }

    @Component
    struct ComponentChild {
      @LocalStorageProp('sessionLocalProp') local_prop_value: string = 'Hello';
      @LocalStorageLink('sessionLocalLink') local_link_value: string = 'Hello';
      @StorageProp('sessionProp') storage_prop_value: string = 'Hello';
      @StorageLink('sessionLink') storage_link_value: string = 'Hello';
      @Consume consume_value: string;
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

3. 当成员变量被private访问限定符和\@Link/\@ObjectLink装饰器同时修饰，并且通过父组件进行初始化赋值，ArkTS会进行校验并产生告警日志。

    【反例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      @State link_value: string = 'Hello';
      @State objectLink_value: ComponentObj = new ComponentObj();
      build() {
        Column() {
          ComponentChild({link_value: this.link_value, objectLink_value: this.objectLink_value})
        }
        .width('100%')
      }
    }
    
    @Observed
    class ComponentObj {
      count: number = 0;
    }
    @Component
    struct ComponentChild {
      // 此处使用private修饰符时会出现告警日志
      @Link private link_value: string;
      // 此处使用private修饰符时会出现告警日志
      @ObjectLink private objectLink_value: ComponentObj;
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

    编译告警日志如下：
    
    ```ts
    Property 'link_value' can not be decorated with both '@Link' and private.
    Property 'objectLink_value' can not be decorated with both '@ObjectLink' and private.
    ```
    
    【正例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      @State link_value: string = 'Hello';
      @State objectLink_value: ComponentObj = new ComponentObj();
      build() {
        Column() {
          ComponentChild({link_value: this.link_value, objectLink_value: this.objectLink_value})
        }
        .width('100%')
      }
    }

    @Observed
    class ComponentObj {
      count: number = 0;
    }
    @Component
    struct ComponentChild {
      @Link link_value: string;
      @ObjectLink objectLink_value: ComponentObj;
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

4. 当成员变量被protected访问限定符修饰，并且通过父组件进行初始化赋值，ArkTS会进行校验并产生告警日志。

    【反例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      build() {
        Column() {
          ComponentChild({regular_value: 'Hello'})
        }
        .width('100%')
      }
    }
    
    @Component
    struct ComponentChild {
      // 此处使用protected修饰符时会出现告警日志
      protected regular_value: string = 'Hello';
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

    编译告警日志如下：
    
    ```ts
    The member attributes of a struct can not be protected.
    ```
    
    【正例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      build() {
        Column() {
          ComponentChild({regular_value: 'Hello'})
        }
        .width('100%')
      }
    }

    @Component
    struct ComponentChild {
      regular_value: string = 'Hello';
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

5. 当成员变量被private访问限定符、\@Require和@State/@Prop/@Provide/@BuilderParam装饰器同时修饰，并且通过父组件初始化赋值时，ArkTS会进行校验并产生告警日志。

    【反例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      build() {
        Column() {
          ComponentChild({prop_value: 'Hello'})
        }
        .width('100%')
      }
    }
    @Component
    struct ComponentChild {
      // 此处使用private修饰符时会出现告警日志
      @Require @Prop private prop_value: string = 'Hello';
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```

    编译告警日志如下：
    
    ```ts
    Property 'prop_value' can not be decorated with both '@Require' and private.
    Property 'prop_value' is private and can not be initialized through the component constructor.
    ```
    
    【正例】
    ```ts
    @Entry
    @Component
    struct AccessRestrictions {
      build() {
        Column() {
          ComponentChild({prop_value: 'Hello'})
        }
        .width('100%')
      }
    }
    @Component
    struct ComponentChild {
      @Require @Prop prop_value: string = 'Hello';
      build() {
        Column() {
          Text('Hello')
            .fontSize(50)
            .fontWeight(FontWeight.Bold)
        }
      }
    }
    ```