面试问题集锦

Activity与Fragment通信

1. 广播

自定义BroadcastReceiver, 定义IntentFilter的action
动态注册并传参

// 自定义BroadcastReceiver
public class DataBroadcastReceiver extends BroadcastReceiver{
        @Override
        public void onReceiver(Context context, Intent intent){
                Object data = intent.getParcelExtra("data");
                // 数据处理
        }
}

private DataBroadcastReceiver dataBroadcastReceiver;

@Override
protected void onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    // 注册广播
    IntentFilter intentFilter = new IntentFilter();
    intentFilter.addAction("com.broadcast.data");
    dataBroadcastReceiver = new DataBroadcastReceiver();
    registerReceiver(dataBroadcastReceiver,intentFilter);
    return super.onCreateView(inflater, container, savedInstanceState);
}

@Override
protected void onDestroyView() {
    super.onDestroyView();
    unregisterReceiver(dataBroadcastReceiver);
}

public void sendData(Object data){
        Intent intent = new Intent();
        intent.setAction("com.broadcast.data");
        intent.putExtra("data",data);
        sendBroadcast(intent);
}

2. 对象调用 public 方法

public class TestActivity extends AppCompactActivity{
    
    private TestFragment testFragment;
    
    public void test(){
        testFragment = new TestFragment();
        testFragment.doTest();
    }
}

public class TestFragment extends Fragment{
    private TestActivity activity;
    
    public void doTest(){
        Log.d(TAG,"收到消息");
    }
}

3. 接口

public class TestActivity extends Activity{

    private ITest iTest;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        iTest = new TestFragment();
        iTest.doTest();
    }
}

public class TestFragment extends Fragment implements ITest{

    @Override
    public void doTest() {
        Log.i(TAG, "doTest: ");
    }
}

public interface ITest{
    void doTest();
}

4. 观察者

这里模拟一个场景，用户在 Activity 里登录状态发生了改变，Fragment 展示退出登录的 UI。我真实项目里也是采用的观察者模式管理登录状态,因为登录状态的改变牵连到一系列的改变。

public class TestActivity extends Activity {

    final int LOGIN_OUT = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LoginManager.loginStatusChanged(LOGIN_OUT);
    }
}

public class TestFragment extends Fragment implements LoginObserver {
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        /**
         * 订阅事件
         */
        LoginManager.registerLoginObserver(this);
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        /**
         * 反订阅事件
         */
        LoginManager.unregisterLoginObserver(this);
    }

    @Override
    public void loginStatusChange(int status) {
        Log.i(TAG, "loginStatusChange: "+status);
    }
}

public class LoginManager {

    private static ArrayList<LoginObserver> loginObserverList = new ArrayList<>();

    public static void registerLoginObserver(LoginObserver loginObserver){
        loginObserverList.add(loginObserver);
    }

    public static void unregisterLoginObserver(LoginObserver loginObserver){
        loginObserverList.remove(loginObserver);
    }

    public static void loginStatusChanged(int loginstatus){
        for (LoginObserver observer:loginObserverList){
            if (observer!=null){
                observer.loginStatusChange(loginstatus);
            }
        }
    }
}

public interface LoginObserver{

    void loginStatusChange(int status);
}

5. EventBus

看官方说明

Fragment与Activity通信

1. 广播

同上

2. 对象调用 public 方法

public class TestActivity extends Activity {
    
    public void doTest(){
        Log.i(TAG, "doTest: ");
    }
}

public class TestFragment extends Fragment {

    private TestActivity activity;
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (getActivity() instanceof TestActivity){
            activity = getActivity();
        }
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    void test(){
        activity.doTest();
    }
}

3. 接口

public class TestActivity extends Activity implements ITest{
    
    @Override
    public void doTest() {
        Log.i(TAG, "doTest: ");
    }
}

public class TestFragment extends Fragment {

    private ITest iTest;
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof ITest){
            iTest = (ITest) context;
        }
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    void test(){
        iTest.doTest();
    }
}

public interface ITest{
    void doTest();
}

4. 观察者

同1.4，只不过这次是 Fragment 改变用户登录状态，Activiy 观察事件而已。

public class TestActivity extends Activity implements LoginObserver {



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LoginManager.registerLoginObserver(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        LoginManager.unregisterLoginObserver(this);
    }

    @Override
    public void loginStatusChange(int status) {

    }
}

public class TestFragment extends Fragment {

    final int LOGIN_OUT = 0;

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return super.onCreateView(inflater, container, savedInstanceState);
    }


    void doTest(){
        LoginManager.loginStatusChanged(LOGIN_OUT);
    }
}

public class LoginManager {

    private static ArrayList<LoginObserver> loginObserverList = new ArrayList<>();

    public static void registerLoginObserver(LoginObserver loginObserver){
        loginObserverList.add(loginObserver);
    }

    public static void unregisterLoginObserver(LoginObserver loginObserver){
        loginObserverList.remove(loginObserver);
    }

    public static void loginStatusChanged(int loginstatus){
        for (LoginObserver observer:loginObserverList){
            if (observer!=null){
                observer.loginStatusChange(loginstatus);
            }
        }
    }
}

public interface LoginObserver{

    void loginStatusChange(int status);
}

5. EventBus

同上

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