add Service 绑定原理

blogs/Android/Framework/Interview/其他应用组件相关/Service 的绑定原理.md

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+---
+Service 的绑定原理
+---
+
+1. 知道 bindService 的用法
+2. 了解 bindService 的大致流程
+3. bindService 涉及哪些参与者，通信过程是怎样的？
+
+```java
+IRemoteCaller mCaller;
+
+ServiceConnection mServiceConnection = new ServiceConnection(){
+	@Override
+	public void onServiceConnected(ComponentName name, IBinder service) {
+	mCaller = IRemoteCaller.Stub.asInterface(service);
+	mCaller.call();
+	}
+}
+
+Intent service = new Intent(this, MyService.class);
+bindService(service, mServiceConnection, BIND_AUTO_CREATE);
+```
+
+Bind Service 总体流程：
+
+![](https://i.loli.net/2020/03/24/F4HYsiel7phDGBw.png)
+
+```java
+@Override
+boolean bindService(Intent service, ServiceConnection conn, int flags) {
+	return bindServiceCommon(service, conn, flags, ...);
+}
+boolean bindServiceCommon(Intent service, ServiceConnection conn, ...) {
+    IServiceConnection sd;
+    // 为 ServiceConnection 接口生成一个 binder 对象，可用于跨进程传递给 AMS
+    sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), mMainThread.getHandler(), flags);
+    ActivityManagerNative.getDefult().bindService(mMainThread.getApplicationThread(), service, sd, ...);
+}
+IServiceConnection getServiceDispatcher(ServiceConnection c, ...) {
+    ServiceDispatcher sd = null;
+    Map<ServiceConnection, ServiceDispatcher> map = mServices.get(context);
+    if(map != null){
+        sd = map.get(c);
+    }
+    if(sd == null){
+        sd = new ServiceDispatcher(c, context, handler,flags);
+        if(map == null){
+            map = new ArrayMap<ServiceConnection, ServiceDispatcher>();
+            mService.put(context, map);
+        }
+        map.put(c, sd);
+    }
+    return sd.getIServiceConnection();
+}
+ServiceDispatcher(ServiceConnection conn, ...){
+    mIServiceConnection = new InnerConnection(this);
+    mConnection = conn;
+}
+
+static class InnerConnection extends IServiceConnection.Stub {
+    final WeakReference<ServiceDispatcher> mDispatcher;
+    public void connected(ComponentName name, IBinder service) {
+        LoadedApk.ServiceDispatcher sd = mDispatcher.get();
+        if(sd != null){
+            sd.connected(name, service);
+        }
+    }
+}
+void connected(){
+    mActivityThread.post(new RunConnection(name, service, 0));
+}
+
+public void doConnected(ComponentName name, IBinder service) {
+    old = mActiveConnections.get(name);
+    if(old!=null && old.binder == service){
+        return;
+    }
+    if(service != null){
+        info = new ConnectionInfo(service);
+        mActiveConnections.put(name, info);
+    }else{
+        mActiveConnections.remove(name);
+    }
+    if(old != null){
+        mConnection.onServiceDisconnected(name);
+    }
+    if(service != null){
+        mConnection.onServiceConnected(name, service);
+    }
+}
+```
+
+```java
+// AMS#bindServiceLocked
+bindServiceLocked(IApplicationThread caller, ...){
+	//...
+	if((flag&Context.BIND_AUTO_CREATE)!=0){
+		bringUpServiceLocked(s, );
+	}
+	if(s.app != null && b.intent.received){
+        c.conn.connected(s.name, b.intent.binder);
+    }else if(!b.intent.requested){
+        requestServiceBindingLocked(s, b.intent, false);
+    }
+}
+
+```
+