安卓本地绑定(bind)

Question

这里为什么要使用getService方法？

public class LocalBinder extends Binder {
    LocalService getService() {
        return LocalService.this;
    }
}

Answer 1

• BoundService 充当客户端-服务器架构中的服务器。(您可能知道这部分内容)。
• 服务器总是向客户端输出一些服务。该服务可能是公共(public)方法。(如“public void reverse(String)”)。
• getService() 函数用于返回 LocalService 的实例，以便客户端可以通过该实例访问该 BoundService 的公共(public)方法。

下面是Android官方文档中的示例程序

public class LocalService extends Service {
    // Binder given to clients
    private final IBinder mBinder = new LocalBinder();
    // Random number generator
    private final Random mGenerator = new Random();

    /**
     * Class used for the client Binder.  Because we know this service always
     * runs in the same process as its clients, we don't need to deal with IPC.
     */
    public class LocalBinder extends Binder {
        LocalService getService() {
            // Return this instance of LocalService so clients can call public methods
            return LocalService.this;
        }
    }

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    /** method for clients */
    public int getRandomNumber() {
      return mGenerator.nextInt(100);
    }
}

.

public class BindingActivity extends Activity {
    LocalService mService;
    boolean mBound = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    @Override
    protected void onStart() {
        super.onStart();
        // Bind to LocalService
        Intent intent = new Intent(this, LocalService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
    }

    @Override
    protected void onStop() {
        super.onStop();
        // Unbind from the service
        if (mBound) {
            unbindService(mConnection);
            mBound = false;
        }
    }

    /** Called when a button is clicked (the button in the layout file attaches to
      * this method with the android:onClick attribute) */
    public void onButtonClick(View v) {
        if (mBound) {
            // Call a method from the LocalService.
            // However, if this call were something that might hang, then this request should
            // occur in a separate thread to avoid slowing down the activity performance.
            int num = mService.getRandomNumber();
            Toast.makeText(this, "number: " + num, Toast.LENGTH_SHORT).show();
        }
    }

    /** Defines callbacks for service binding, passed to bindService() */
    private ServiceConnection mConnection = new ServiceConnection() {

        @Override
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // We've bound to LocalService, cast the IBinder and get LocalService instance
            LocalBinder binder = (LocalBinder) service;
            mService = binder.getService();
            mBound = true;
        }

        @Override
        public void onServiceDisconnected(ComponentName arg0) {
            mBound = false;
        }
    };
}

让我们仔细看看。

服务器部分。

公共(public)类 LocalService 是向客户端 Activity 或服务导出(或提供)某些功能的服务。客户端导入(或使用)功能。

public int getRandomNumber() { 返回 mGenerator.nextInt(100); }

以上代码是服务器输出的实际功能或服务。

客户端部分。

LocalBinder binder = (LocalBinder) 服务； mService = binder.getService(); mBound = true;

这里的 binder.getService() 用于获取 LocalBinder 类的运行(或当前)实例(或对象)。

然后，

int num = mService.getRandomNumber(); Toast.makeText(this, "number: "+num,Toast.LENGTH_SHORT).show();

mService.getRandomNumber() 用于访问公共(public)方法。