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1# 远端状态订阅开发实例
2
3IPC/RPC提供对远端Stub对象状态的订阅机制，在远端Stub对象消亡时，可触发消亡通知告诉本地Proxy对象。这种状态通知订阅需要调用特定接口完成，当不再需要订阅时也需要调用特定接口取消。使用这种订阅机制的用户，需要实现消亡通知接口DeathRecipient并实现onRemoteDied方法清理资源。该方法会在远端Stub对象所在进程消亡或所在设备离开组网时被回调。值得注意的是，调用这些接口有一定的顺序。首先，需要Proxy订阅Stub消亡通知，若在订阅期间Stub状态正常，则在不再需要时取消订阅；若在订阅期间Stub所在进程退出或者所在设备退出组网，则会自动触发Proxy自定义的后续操作。
4
5## 使用场景
6
7这种订阅机制适用于本地Proxy对象需要感知远端Stub对象所在进程消亡，或所在设备离开组网的场景。当Proxy感知到Stub端消亡后，可适当清理本地资源。此外，RPC目前不提供匿名Stub对象的消亡通知，即只有向SAMgr注册过的服务才能被订阅消亡通知，IPC则支持匿名对象的消亡通知。
8
9
10## Native侧接口
11
12| 接口名 | 返回值类型 | 功能描述 |
13| -------- | -------- | -------- |
14| AddDeathRecipient(const sptr\<DeathRecipient> &recipient); | bool | 订阅远端Stub对象状态。 |
15| RemoveDeathRecipient(const sptr\<DeathRecipient> &recipient); | bool | 取消订阅远端Stub对象状态。 |
16| OnRemoteDied(const wptr\<IRemoteObject> &object); | void | 当远端Stub对象死亡时回调。 |
17
18### 参考代码
19
20```C++
21#include "iremote_broker.h"
22#include "iremote_stub.h"
23
24//定义消息码
25enum {
26    TRANS_ID_PING_ABILITY = 5,
27    TRANS_ID_REVERSED_MONITOR
28};
29
30const std::string DESCRIPTOR = "test.ITestAbility";
31
32class ITestService : public IRemoteBroker {
33public:
34    // DECLARE_INTERFACE_DESCRIPTOR是必需的，入参需使用std::u16string；
35    DECLARE_INTERFACE_DESCRIPTOR(to_utf16(DESCRIPTOR));
36    virtual int TestPingAbility(const std::u16string &dummy) = 0; // 定义业务函数
37};
38
39class TestServiceProxy : public IRemoteProxy<ITestAbility> {
40public:
41    explicit TestAbilityProxy(const sptr<IRemoteObject> &impl);
42    virtual int TestPingAbility(const std::u16string &dummy) override;
43    int TestAnonymousStub();
44private:
45    static inline BrokerDelegator<TestAbilityProxy> delegator_; // 方便后续使用iface_cast宏
46};
47
48TestServiceProxy::TestServiceProxy(const sptr<IRemoteObject> &impl)
49    : IRemoteProxy<ITestAbility>(impl)
50{
51}
52
53int TestServiceProxy::TestPingAbility(const std::u16string &dummy){
54    MessageOption option;
55    MessageParcel dataParcel, replyParcel;
56    dataParcel.WriteString16(dummy);
57    int error = PeerHolder::Remote()->SendRequest(TRANS_ID_PING_ABILITY, dataParcel, replyParcel, option);
58    int result = (error == ERR_NONE) ? replyParcel.ReadInt32() : -1;
59    return result;
60}
61```
62
63```c++
64#include "iremote_object.h"
65
66class TestDeathRecipient : public IRemoteObject::DeathRecipient {
67public:
68    virtual void OnRemoteDied(const wptr<IRemoteObject>& remoteObject);
69}
70
71void TestDeathRecipient::OnRemoteDied(const wptr<IRemoteObject>& remoteObject)
72{
73}
74```
75
76```c++
77sptr<IPCObjectProxy> object = new IPCObjectProxy(1, to_utf16(DESCRIPTOR));
78sptr<IRemoteObject::DeathRecipient> deathRecipient (new TestDeathRecipient());// 构造一个消亡通知对象
79bool result = object->AddDeathRecipient(deathRecipient); // 注册消亡通知
80result = object->RemoveDeathRecipient(deathRecipient); // 移除消亡通知
81```
82
83## JS侧接口
84
85| 接口名                   | 返回值类型 | 功能描述                                                          |
86| ------------------------ | ---------- | ----------------------------------------------------------------- |
87| registerDeathRecipient   | void       | 注册用于接收远程对象消亡通知的回调，增加 proxy 对象上的消亡通知。 |
88| unregisterDeathRecipient | void       | 注销用于接收远程对象消亡通知的回调。                              |
89| onRemoteDied             | void       | 在成功添加死亡通知订阅后，当远端对象死亡时，将自动调用本方法。    |
90
91### 获取context
92
93Stage模型在连接服务前需要先获取context
94
95```ts
96import Ability from "@ohos.app.ability.UIAbility";
97
98export default class MainAbility extends Ability {
99    onCreate(want, launchParam) {
100        console.log("[Demo] MainAbility onCreate");
101        globalThis.context = this.context;
102    }
103    onDestroy() {
104        console.log("[Demo] MainAbility onDestroy");
105    }
106    onWindowStageCreate(windowStage) {
107        // Main window is created, set main page for this ability
108        console.log("[Demo] MainAbility onWindowStageCreate");
109    }
110    onWindowStageDestroy() {
111        // Main window is destroyed, release UI related resources
112        console.log("[Demo] MainAbility onWindowStageDestroy");
113    }
114    onForeground() {
115        // Ability has brought to foreground
116        console.log("[Demo] MainAbility onForeground");
117    }
118    onBackground() {
119        // Ability has back to background
120        console.log("[Demo] MainAbility onBackground");
121    }
122}
123```
124
125### 参考代码
126
127```ts
128// 仅FA模型需要导入@ohos.ability.featureAbility
129// import FA from "@ohos.ability.featureAbility";
130
131let proxy;
132let connect = {
133    onConnect: function(elementName, remoteProxy) {
134        console.log("RpcClient: js onConnect called.");
135        proxy = remoteProxy;
136    },
137    onDisconnect: function(elementName) {
138        console.log("RpcClient: onDisconnect");
139    },
140    onFailed: function() {
141        console.log("RpcClient: onFailed");
142    }
143};
144let want = {
145    "bundleName": "com.ohos.server",
146    "abilityName": "com.ohos.server.MainAbility",
147};
148// FA模型通过此方法连接服务
149// FA.connectAbility(want, connect);
150
151globalThis.context.connectServiceExtensionAbility(want, connect);
152
153class MyDeathRecipient {
154    onRemoteDied() {
155        console.log("server died");
156    }
157}
158let deathRecipient = new MyDeathRecipient();
159proxy.registerDeathRecippient(deathRecipient, 0);
160proxy.unregisterDeathRecipient(deathRecipient, 0);
161```
162
163## Stub感知Proxy消亡（匿名Stub的使用）
164
165正向的消亡通知是Proxy感知Stub的状态，若想达到反向的死消亡通知，即Stub感知Proxy的状态，可以巧妙的利用正向消亡通知。如两个进程A（原Stub所在进程）和B（原Proxy所在进程），进程B在获取到进程A的Proxy对象后，在B进程新建一个匿名Stub对象（匿名指未向SAMgr注册），可称之为回调Stub，再通过SendRequest接口将回调Stub传给进程A的原Stub。这样一来，进程A便获取到了进程B的回调Proxy。当进程B消亡或B所在设备离开组网时，回调Stub会消亡，回调Proxy会感知，进而通知给原Stub，便实现了反向消亡通知。
166
167注意：
168
169> 反向死亡通知仅限设备内跨进程通信使用，不可用于跨设备。
170
171> 当匿名Stub对象没有被任何一个Proxy指向的时候，内核会自动回收。
172
173### 参考代码
174
175```c++
176//Proxy
177int TestAbilityProxy::TestAnonymousStub()
178{
179    MessageOption option;
180    MessageParcel dataParcel, replyParcel;
181    dataParcel.UpdateDataVersion(Remote());
182    dataParcel.WriteRemoteObject(new TestAbilityStub());
183    int error = Remote()->SendRequest(TRANS_ID_REVERSED_MONITOR,dataParcel, replyParcel, option);
184    int result = (error == ERR_NONE) ? replyParcel.ReadInt32() : -1;
185    return result;
186}
187
188//Stub
189
190int TestAbilityStub::OnRemoteRequest(uint32_t code, MessageParcel &data, MessageParcel &reply, MessageOption &option)
191{
192    switch (code) {
193        case TRANS_ID_REVERSED_MONITOR: {
194            sptr<IRemoteObject> obj = data.ReadRemoteObject();
195            if (obj == nullptr) {
196                reply.WriteInt32(ERR_NULL_OBJECT);
197                return ERR_NULL_OBJECT;
198            }
199            bool result = obj->AddDeathRecipient(new TestDeathRecipient());
200            result ? reply.WriteInt32(ERR_NONE) : reply.WriteInt32(-1);
201            break;
202        }
203        default:
204            break;
205    }
206    return ERR_NONE;
207}
208```
209
210