BroadCast,BroadCastReceiver

效果是：一个MainActivity动态注册一个BroadcastReceiver，BActivity发送一个标准广播，MainActivity接收到广播后，将广播中的消息显示在MainActivity的TextView上。

MainActivity：
（实现端）
public class MainActivity extends AppCompatActivity implements IUpdateNumLitener{
    private TextView mNumTextView;
    private Button mStartButton;
    //广播接收器
    private NumReceiver mReceiver;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //3、注册广播---哪个画面需要监听广播，在哪个画面注册
        mReceiver = new NumReceiver();
        //4-3 在实现端实现接口，并把接口传给触发端
        mReceiver.setUpdateNumLitener(this);
        IntentFilter filter = new IntentFilter();
        filter.addAction("org.mobiletrain.add");
        registerReceiver(mReceiver, filter);
        mNumTextView = (TextView)findViewById(R.id.num_textview);
        mStartButton = (Button)findViewById(R.id.start_button);
        mStartButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, BActivity.class);
                startActivity(intent);
            }
        });

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //3 取消注册
        unregisterReceiver(mReceiver);
    }

    @Override
    public void getText( String txt) {
        mNumTextView.setText(txt);
    }
}

BActivity

public class BActivity extends AppCompatActivity {
    private Button mAddButton;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_b);
        mAddButton = (Button)findViewById(R.id.add_button);
        mAddButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                add();
            }
        });
    }

    private void add() {
        //1、发送广播
        Intent intent = new Intent("org.mobiletrain.add");
        intent.putExtra("key","内容");
        sendBroadcast(intent);
    }
}

广播接收器BroadcastReceiver
（触发端）

public class NumReceiver extends BroadcastReceiver {
    private IUpdateNumLitener iUpdateNumLitener;
    @Override
    public void onReceive(Context context, Intent intent) {
        String txt = intent.getStringExtra("key");
        iUpdateNumLitener.getText(txt);
    }
    //4-3 在实现端实现接口，并把接口传给触发端
    //接收接口的方法
    public void setUpdateNumLitener (IUpdateNumLitener updateNumLitener) {
        this.iUpdateNumLitener = updateNumLitener;
    }
}

接口

//4-1 定义接口，封装抽象方法
public interface IUpdateNumLitener {
   void update();
}