活动到活动回调监听器

Question

假设有两个活动Activity1 和Activity2。我需要从methodAct2（Activity2 内部）调用方法methodAct1()（Activity1 内部）。我认为它应该使用回调侦听器工作 - 我不想使用 EventBus libs！

我使用此代码得到java.lang.NullPointerException：

界面：

public interface MyListener {
    public void listen();
}

创建事件的活动：

public class Activity2 extends Activity {

    private MyListener  myListener;

    public void setUpListener(MyListener myListener) {
        this.myListener = myListener;
    }

    private void doWork(){
        //do stuff 
        myListener.listen();
    }
}

我希望在工作完成后获得该事件的活动：

public class Activity1 extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Activity2 activity2 = new Activity2();
        activity2.setUpListener(new setUpListener() {
            @Override
            public void listen() {
                // get the event here

            }
        });
    }
}

Answer 1

这是绝对不可能的。你永远不会自己实例化一个新的 Activity。您不会同时运行两个活动。

如果您希望另一个 Activity 根据您之前的 Activity 想要做某事，那么您需要将其添加到您的 Intent 中。

Intent intent = new Intent(this, Activity2.class);
intent.putExtra("data field", "data value");
startActivity(intent);

如果您希望通过回调实现特定功能，那么您可能会考虑Fragments。通过这种方式，您可以运行相同的 Activity，它可以告诉各个 Fragment 他们需要做什么。

Answer 2

由于您的陈述，NPE 正在发生：

Activity2 activity2 = new Activity2(); <--

你不应该这样做，而是应该在活动 1 中这样做：

Intent intent = new Intent(this, Activity2.class);
intent.putExtra("dataKey", "dataValue");
startActivityForResult(pickContactIntent, CALLBACK_REQUEST);

startActivityForResult() 提供从 Activity 2 到 Activity 1 的回调，您必须覆盖 Activity 1 中的结果：

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // Check which request we're responding to
    if (requestCode == CALLBACK_REQUEST) {
        // Make sure the request was successful
        if (resultCode == RESULT_OK) {
            // The Intent's data Uri identifies which contact was selected.

            // Do something with the contact here (bigger example below)
        }
    }
}

Answer 3

你可以像这样用你的方法做到这一点......

public class Activity2 extends AppCompatActivity {

    private static MyListener  myListener;

    public static void setUpListener(MyListener Listener) {
        myListener = Listener;
    }

    public void doWork(View view) {
        myListener.listen();
    }
}


public class Activity1 extends AppCompatActivity {

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

        Activity2.setUpListener(new MyListener() {
            @Override
            public void listen() {
                Log.d("Hello", "Hello World");
            }
        });
    }

    public void goToAnotherActivity(View view) {
        startActivity(new Intent(Activity1.this, Activity2.class));
    }
}

虽然这不是最好的方法，但为了使用这种机制，您需要创建 activity1。

Answer 4

你可以这样做> - STEP 01：实现共享接口

---

public interface SharedCallback {
    public String getSharedText(/*you can define arguments here*/);
}

• 步骤 02：实现共享类

---

final class SharedMethode {
    private static Context mContext;

    private static SharedMethode sharedMethode = new SharedMethode();

    private SharedMethode() {
        super();
    }

    public static SharedMethode getInstance() {
        return sharedMethode;
    }

    public void setContext(Context context) {
        if (mContext != null)
            return;

        mContext = context;
    }

    public boolean contextAssigned() {
        return mContext != null;
    }

    public Context getContext() {
        return mContext;
    }

    public void freeContext() {
        mContext = null;
    }
}

- STEP 03 :: 在第一个活动中玩代码

---

public class FirstActivity extends Activity implements SharedCallback {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.your_layout);

        // call playMe from here or there
        playMe();
    }

    private void playMe() {
        SharedMethode.getInstance().setContext(this);
        Intent intent = new Intent(this, SecondActivity.class);
        startActivity(intent);
    }

    @Override
    public String getSharedText(/*passed arguments*/) {
        return "your result";
    }

}

• 步骤 04 :: 在 SecondActivity 中完成游戏

---

public class SecondActivity extends Activity {

    private SharedCallback sharedCallback;

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

        if (SharedMethode.getInstance().contextAssigned()) {
            if (SharedMethode.getInstance().getContext() instanceof SharedCallback)
                sharedCallback = (SharedCallback) SharedMethode.getInstance().getContext();

            // to prevent memory leak. no further needs
            SharedMethode.freeContext();
        }

        // You can now call your implemented methodes from anywhere at any time
        if (sharedCallback != null)
            Log.d("TAG", "Callback result = " + sharedCallback.getSharedText());

    }

        @Override
        protected void onDestroy() {
        sharedCallback = null;
        super.onDestroy();
    }

}

你也可以实现一个 backword 回调（从 First 到 Second）来从 SecondAvtivity 中获取一些结果或者调用一些方法