Question

刚开始学习android。请帮忙。我有三个片段，每个片段都有一个必须运行媒体播放器其中一个流的按钮。如何在片段中找到我的活动按钮，该按钮稍后会附加到特定的流中？试图引用该按钮，以便：

btnStart =（Button）titleAdapter.frags [0] .getView（）。findViewById（R.id.btnStart）;

没用，错误java.lang.NullPointerException，我做错了

public class TitleAdapter extends FragmentPagerAdapter {
    private final String titles[] = new String[] { "FragA", "FragB", "FragC" };
    private final Fragment frags[] = new Fragment[titles.length];
    public TitleAdapter(FragmentManager fm) {
        super(fm);
        frags[0] = new FragmentA();
        frags[1] = new FragmentB();
        frags[2] = new FragmentC();
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Log.v("TitleAdapter - getPageTitle=", titles[position]);
        return titles[position];
    }

    @Override
    public Fragment getItem(int position) {
        Log.v("TitleAdapter - getItem=", String.valueOf(position));
        return frags[position];
    }

    @Override
    public int getCount() {
        return frags.length;
    }
}

代码MainActivity.java：

    public class MainActivity extends FragmentActivity {

      final static String LOG_TAG = "myLogs";
      static MediaPlayer mediaPlayer;
      static AudioManager am;
      static CheckBox pdaStream;
      static Button btnNews;
      ViewPager mViewPager;

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

        mViewPager = (ViewPager) findViewById(R.id.pager);


        TitleAdapter titleAdapter = new TitleAdapter(getSupportFragmentManager());
        mViewPager.setAdapter(titleAdapter);
        mViewPager.setCurrentItem(1);
        mViewPager.setOffscreenPageLimit(2);

        pdaStream = (CheckBox) findViewById(R.id.pdaStream);
        am = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
        SeekBar music = (SeekBar)findViewById(R.id.seekBar1);
        initBar(music, AudioManager.STREAM_MUSIC);
    }

    @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;
    }

    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()) {
        case R.id.news:
            Intent intent = new Intent(this, RSSActivity.class);
            startActivity(intent);
          break;
        default:
          break;
        }
        return super.onOptionsItemSelected(item);
    }


    public static void initBar(SeekBar bar, final int stream) {
          bar.setMax(am.getStreamMaxVolume(stream));
          bar.setProgress(am.getStreamVolume(stream));

          bar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            public void onProgressChanged(SeekBar bar, int progress,
                                          boolean fromUser) {
              am.setStreamVolume(stream, progress,
                                  AudioManager.FLAG_PLAY_SOUND);
            }

            public void onStartTrackingTouch(SeekBar bar) {
              // no-op
            }

            public void onStopTrackingTouch(SeekBar bar) {
              // no-op
            }
          });
        }
}

代码片段类似，这里是其中之一

代码FragmentA.java：

public class FragmentA extends Fragment {

  final static String LOG_TAG = "myLogs";  
  private static ProgressBar progressBar;
      static CheckBox pdaStream;



    public FragmentA() {
    }

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

    final Button Play = (Button) rootView.findViewById(R.id.btnStart);
    progressBar = (ProgressBar) rootView.findViewById(R.id.progressBar);
    progressBar.setVisibility(View.GONE);
    pdaStream = (CheckBox) getActivity().findViewById(R.id.pdaStream);

       return rootView;
    }   }

activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/RelativeLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/background"
tools:context=".MainActivity" >


<android.support.v4.view.PagerTabStrip
    android:id="@+id/pager_title_strip"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="top"
    android:background="@drawable/bg_pager"
    android:paddingBottom="4dp"
    android:paddingTop="4dp"
    android:textColor="#fff" />
</android.support.v4.view.ViewPager>

<SeekBar
    android:id="@+id/seekBar1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_marginBottom="60dp"
    android:layout_marginLeft="10dp"
    android:layout_marginRight="10dp"
    android:thumb="@drawable/seek" />

<CheckBox
    android:id="@+id/pdaStream"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_marginBottom="10dp"
    android:layout_marginLeft="10dp"
    android:layout_marginRight="10dp"
    android:layout_marginTop="70dp"
    android:text="@string/chkbox" />

</RelativeLayout>

fragment_a.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/RelativeLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<Button
    android:id="@+id/btnStart"
    android:layout_width="70dp"
    android:layout_height="70dp"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:textSize="16sp" 
    android:onClick="onClick"
    android:background="@drawable/play_button"/>

<ProgressBar
    android:id="@+id/progressBar"
    style="?android:attr/progressBarStyleLarge"
    android:layout_width="150dp"
    android:layout_height="150dp"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true" />


</RelativeLayout>

Answer 1

public static Fragment getCurrentFragment(ViewPager pager, FragmentPagerAdapter adapter) {
    try {
        Method m = adapter.getClass().getSuperclass().getDeclaredMethod("makeFragmentName", int.class, long.class);
        Field f = adapter.getClass().getSuperclass().getDeclaredField("mFragmentManager");
        f.setAccessible(true);
        FragmentManager fm = (FragmentManager) f.get(adapter);
        m.setAccessible(true);
        String tag = null;
        tag = (String) m.invoke(null, pager.getId(), (long) pager.getCurrentItem());
        return fm.findFragmentByTag(tag);
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    } catch (IllegalArgumentException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    } 
    return null;
}

然后在FragmentA.java中添加一个公共getter按钮，

public Button getPlayButton()
{ 
    return Play;
}

片段活动中的

，

Fragment currenFragment = getCurrentFragmet(mViewPager,titleAdapter);
if(currenFragment!=null){
     // cast the fragment to FragmentA class, then call getter
    ((FragmentA)currentFragment).getPlayButton();
}

Answer 2

在片段<{1}}中使用以下代码

onActivityCreated()

如何找到Activity片段中的按钮

2 个答案: