从 Activity 调用 ViewPager 中当前 Fragment 的方法

Question

我正在一个 android 应用程序中监听网络活动。当事件通过网络传来时，我想更新一些驻留在我的应用程序中不同片段内的 TextView。现在我有一个单屏应用程序，其中一次在屏幕上显示一个 Fragment。

如何在 ViewPager 中调用由 FragmentStatePagerAdapter 管理的现有 Fragment 的方法？

我能够正确地“绘制”用户界面，它按预期显示在屏幕上。这一切都有效。当后台线程向我的包含活动发送消息时，我遇到的困难是调用一个方法。该线程运行时间很长，并且会频繁更新每个 TextView（想想倒计时）。

{thread} -> Actvity.handleMessage() -> {current}Fragment.update();

我试图辨别“当前”的屏幕片段是什么，以便我可以调用它的方法来更新它的 TextViews。我正在尝试使用我读过的 findFragmentByTag 方法，但它总是返回一个 null Fragment 对象。

具体来说，我正在这样做：

private String getFragmentTag(int viewPagerId, int fragmentPosition){
     return "android:switcher:" + viewPagerId + ":" + fragmentPosition;
}

//Take the data from the thread (network) and react to it.
@Override
public boolean handleMessage(Message msg) {
    //tell the fragment to update itself        
    //Log.v(TAG, "Handler: " + msg.what);

    int currentFragmentIndex = pager.getCurrentItem();
    Log.v(TAG, "Current Fragment Index: " + Integer.toString(currentFragmentIndex));

    String fTag = getFragmentTag(pager.getId(), currentFragmentIndex );
    Log.v(TAG, "Current Fragment Tag: " + fTag);

    ////THIS IS WHERE I AM HAVING TROUBLE!////
    Log.v(TAG, "fragment: " + getSupportFragmentManager().findFragmentByTag(fTag));
    ////THIS ALWAYS OUTPUTS:
    ////fragment: null



    //now do the update
    //currentFragment.update(sensorDataMap);

    return true;
}

基于阅读大量内容，特别是这篇文章 - How to get existing fragments when using FragmentPagerAdapter

这里是相关代码...

MainActivity.java

public class MainActivity extends FragmentActivity implements Callback {
    //receive messages from the other thread
    private  Handler handler = new Handler(this);

    //the runnable listening to the network
    private UDPListener udpl;

    //we will parse the handler data into this map and store the values by int keys
    private SparseArray<String> sensorDataMap = new SparseArray<String>();

    //for logging and convenience
    private static final String TAG = "BRRT";   

    //set up the fragment manager
    private ViewPager pager;
    private ScreenFragmenStatePagerAdapter fragmentManager;
    private ScreenFragment currentFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //remove the titlebar
        this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

        //keep the screen on while we are running
        this.getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

        //set up the pager to move through the fragments
        pager = (ViewPager) findViewById(R.id.viewPager);
        fragmentManager = new ScreenFragmenStatePagerAdapter(getSupportFragmentManager());
        pager.setAdapter(fragmentManager);

        //start up the thread
        Log.v(TAG, "start thread");
        startUDPListener(handler);
        Log.v(TAG, "past start thread");    
    }


    //start up the thread to listen to the network, pass in the handle to this thread for messages
    private void startUDPListener(Handler handler){
        //spawn the listener thread, pass in the context and the handler object
        try{
            udpl = new UDPListener(this.getApplicationContext(), handler, sensorDataMap);

            //TODO remove this debug flag
            //DEBUG
            udpl.setDebug(true);
            //DEBUG 

            //set up the threaded reading, event throwing
            Thread reader = new Thread(udpl);
            reader.start();

        } catch(Exception e){
            //TODO real logging
            Log.v(TAG, "caught after trying to start thread");
            Log.v(TAG, e.getMessage());
        }

    }

    //fragile, as this depends on the current naming convention for these fragment IDs in support/v4.
    private String getFragmentTag(int viewPagerId, int fragmentPosition){
         return "android:switcher:" + viewPagerId + ":" + fragmentPosition;
    }

    //Take the data from the thread (network) and react to it. This will get back unparsed strings
    //and have to parse them in this thread, with the UI
    @Override
    public boolean handleMessage(Message msg) {
        //tell the fragment to update itself        
        //Log.v(TAG, "Handler: " + msg.what);

        int currentFragmentIndex = pager.getCurrentItem();
        Log.v(TAG, "Current Fragment Index: " + Integer.toString(currentFragmentIndex));

        String fTag = getFragmentTag(pager.getId(), currentFragmentIndex );
        Log.v(TAG, "Current Fragment Tag: " + fTag);


        Log.v(TAG, "fragment: " + getSupportFragmentManager().findFragmentByTag(fTag));
        //Log.v(TAG, "Current Fragment Null? " + (currentFragment == null));


        //now do the update
        //currentFragment.update(sensorDataMap);

        return true;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

}

ScreenFragmenStatePagerAdapter .java

public class ScreenFragmenStatePagerAdapter extends FragmentStatePagerAdapter {
    //the set of screens we are interested in.
    private ArrayList<ScreenConfig> screens = new ArrayList<ScreenConfig>(6);

    //for logging and convenience
    private static final String TAG = "CC";

    //convenience variable to let us know what screen we are pointing at, logically
    private ScreenConfig currentScreenConfig;

    public ScreenFragmenStatePagerAdapter(FragmentManager fm) {
        super(fm);

        //set up the data.
        setupScreenData();
    }


    @Override
    public Fragment getItem(int pos) {
        //Log.v(TAG, "fragment pos: " + pos);   

        //hopefully this will always work
        currentScreenConfig = screens.get(pos);
        ScreenFragment sf;

        if (currentScreenConfig.eventCount() == 1){
            sf = OneUpScreen.newInstance();
        } else {
            sf = FourUpScreen.newInstance();
        }

        sf.setConfig(currentScreenConfig);
        return sf;
    }


    @Override
    public int getCount() {
        return screens.size();
    }


    //class that maps the various events to their descriptions in a screen by screen way
    //do all the grunt work of mapping screens to events
    private void setupScreenData(){
        //TODO convert this stuff to JSON so we can pass them around in Bundles

        //a 1up screen
        ScreenConfig configGun = new ScreenConfig("Gun");
        configGun.addEvent(204, "TimeToGun","Ttg", "TTG");
        screens.add(configGun);

        //the rest are 4up screens
        ScreenConfig configBowman = new ScreenConfig("Bowman");
        configBowman.addEvent(5, "ExTws","Tws", "TWS");
        configBowman.addEvent(34, "ExLayTimeOnStrb", "LayTimeOnStrb", "Time Stb");
        configBowman.addEvent(37, "ExLayTimeOnPort", "LayTimeOnPort", "Time Prt");
        configBowman.addEvent(113, "ExNextMarkTwa", "NextMarkTwa", "TWA");
        screens.add(configBowman);

        ScreenConfig configPit = new ScreenConfig("Pit");
        configPit.addEvent(88, "ExMarkTime","MarkTime", "Time Mark");
        configPit.addEvent(113, "ExNextMarkTwa", "NextMarkTwa", "Next TWA");
        configPit.addEvent(111, "ExNextMarkRng", "NextMarkRng", "Next Range");
        configPit.addEvent(112, "ExNextMarkBrg", "NextMarkBrg", "Next Brg");        
        screens.add(configPit);

        ScreenConfig configUpwindTrimmer = new ScreenConfig("Upwind Trimmer");
        configUpwindTrimmer.addEvent(5, "ExTws","Tws", "TWS");
        configUpwindTrimmer.addEvent(1, "ExBsp", "Bsp", "BSP");
        configUpwindTrimmer.addEvent(54, "ExTargBspN", "TargBspN", "Tgt BSP");
        configUpwindTrimmer.addEvent(4, "ExTwa", "Twa", "TWA");     
        screens.add(configUpwindTrimmer);   

        ScreenConfig configDownwindTrimmer = new ScreenConfig("Downwind Trimmer");
        configDownwindTrimmer.addEvent(5, "ExTws","Tws", "TWS");
        configDownwindTrimmer.addEvent(4, "ExTwa", "Twa", "TWA");
        configDownwindTrimmer.addEvent(53, "ExTargTwaN", "TargTwaN", "Tgt BSP");
        configDownwindTrimmer.addEvent(58, "ExPolarBspPercent", "PolarBspPercent", "P Bsp %");      
        screens.add(configDownwindTrimmer);

        ScreenConfig configHelmsman = new ScreenConfig("Helmsman");
        configHelmsman.addEvent(5, "ExTws","Tws", "TWS");
        configHelmsman.addEvent(1, "ExBsp", "Bsp", "BSP");
        configHelmsman.addEvent(6, "ExTwd", "Twd", "TWD");
        configHelmsman.addEvent(4, "ExTwa", "Twa", "TWA");      
        screens.add(configHelmsman);

    }
}

activty_main.xml

<android.support.v4.view.ViewPager
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/viewPager"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" />

Answer 1

好吧，我放弃了正常的方式，转而使用绿色机器人基于EventBus的架构。

以下是相关的 java 文件，可帮助您了解我在此问题上的最终结果。我基本上转向在我的网络线程中发布到 EventBus 并直接在我的片段中接收这些事件。它大大简化了我的代码。对代码有很多优化（比如将 Fragment 和 Activity 生命周期处理程序拉入中心类或接口），但那是在未来。

这是 MainActivity.java 文件。现在它所做的一切（基本上）就是设置 viewpager 并启动网络线程。

public class MainActivity extends FragmentActivity {
    //the runnable listening to the network
    private UDPListener udpl;

    //for logging and convenience
    private static final String TAG = "BRRT";   

    //set up the fragment manager
    private ViewPager pager;
    private ScreenFragmenStatePagerAdapter fragmentManager;

    //we will parse the handler data into this map and store the values by int keys
    private SparseArray<String> sensorDataMap = new SparseArray<String>();


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //remove the titlebar
        this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

        //keep the screen on while we are running
        this.getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

        //set up the pager to move through the fragments
        pager = (ViewPager) findViewById(R.id.viewPager);
        fragmentManager = new ScreenFragmenStatePagerAdapter(getSupportFragmentManager());
        pager.setAdapter(fragmentManager);
    }

    @Override
    public void onResume(){

        //start up the thread
        Log.v(TAG, "start thread");
        startUDPListener();
        Log.v(TAG, "past start thread");    

        super.onResume();
    }


    //start up the thread to listen to the network, pass in the handle to this thread for messages
    private void startUDPListener(){
        //spawn the listener thread, pass in the context and the handler object
        try{
            udpl = new UDPListener(this.getApplicationContext(), sensorDataMap);

            //TODO remove this debug flag
            //DEBUG
            udpl.setDebug(true);
            //DEBUG 

            //set up the threaded reading, event throwing
            Thread reader = new Thread(udpl);
            reader.start();

        } catch(Exception e){
            //TODO real logging
            Log.v(TAG, "caught after trying to start thread");
            Log.v(TAG, e.getMessage());
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

}

这是一个片段。它所做的只是配置它的视图，并监听 EventBus 上的事件。

public class OneUpScreen extends ScreenFragment {   
    private Button name;
    private TextView c00Title, c00Data;

    //DEBUG
    public String title;

    //DEBUG
    private int counter = 0;

    //for logging and convenience
    private static final String TAG = "BRRT";   


    @Override
    public void onResume(){
        EventBus.getDefault().register(this);
        super.onResume();
    }

    @Override
    public void onDestroy(){
        EventBus.getDefault().unregister(this);
        super.onDestroy();
    }

    //process the bus messaging
    public void onEventMainThread(ExpeditionEvent event){      <-- READ IT FROM THE BUS
        Log.v(TAG, "OneUp event received: " + event.getEventId() + " : " + event.getEventScreenValue());
        c00Data.setText(""+counter);
        counter++;
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.one_up_screen_layout, container, false);

        name = (Button) v.findViewById(R.id.lblTitle);
        c00Title = (TextView) v.findViewById(R.id.c00Title);
        c00Data = (TextView) v.findViewById(R.id.c00Data);

        Bundle bundle = this.getArguments();

        //initial set up of the text on the screen
        //null check
        name.setText((bundle.getString("name") == null) ? "error" : bundle.getString("name"));
        c00Title.setText((bundle.getString("c00Title") == null) ? "error" : bundle.getString("c00Title"));
        title = bundle.getString("c00Title");

        return v;
    }

    public OneUpScreen(){

    }

    public static OneUpScreen newInstance() {
        OneUpScreen frag = new OneUpScreen();
        return frag;
    }

    //attach the config for this instance.
    @Override
    public void setConfig(ScreenConfig sc){
        //set up the data to paint the screen for the first time
        Bundle b = new Bundle();

        //now we have to parse some stuff into a bundle and send the bundle to the fragment
        b.putString("name", sc.getName());
        b.putString("c00Title", sc.getEvents().get(0).getCleanName());
        b.putInt("c00Data", sc.getEvents().get(0).getEventID());

        //pass it along
        this.setArguments(b);
    }

}

这是我在网络监听器中调用的，这是在Runnable的run)方法中...

//throw out an event for each item
EventBus.getDefault().post(new ExpEvent(key, value));   <-- PUT IT ON THE BUS

塔达！！！

我希望这能帮助下一个在 Android 中遇到 ViewPager、FragmentStatePagerAdapters、Fragments 或线程问题的人。