我正在制作一个带有三个TabLayouts（使用片段）的MusicPlayer应用程序和一个带有从基本适配器扩展的自定义阵列适配器的Listview。
在内容解析器和Uris的帮助下显示歌曲。
但是每当我尝试运行应用程序时，应用程序都会崩溃。 我不知道是什么问题。
这是我的SongAdapter（ArrayAdapter）.java
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.TextView;
import java.util.ArrayList;
public class SongAdapter extends BaseAdapter {
private ArrayList<Song> songs;
private LayoutInflater songInf;
public SongAdapter(Context c, ArrayList<Song> theSongs){
songs=theSongs;
songInf=LayoutInflater.from(c);
}
@Override
public int getCount() {
return songs.size();
}
@Override
public Object getItem(int i) {
return null;
}
@Override
public long getItemId(int i) {
return 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
//map to song layout
LinearLayout songLay = (LinearLayout)songInf.inflate
(R.layout.songviewer, parent, false);
//get title and artist views
TextView songView = (TextView)songLay.findViewById(R.id.song_title);
TextView artistView = (TextView)songLay.findViewById(R.id.song_artist);
//get song using position
Song currSong = songs.get(position);
//get title and artist strings
songView.setText(currSong.getTitle());
artistView.setText(currSong.getArtist());
//set position as tag
songLay.setTag(position);
return songLay;
}
}
MainActivity.java
MainActivity.java要求从设备外部存储设备中获取歌曲的权限。
public class MainActivity extends AppCompatActivity {
private Toolbar toolbar;
private TabLayout tabLayout;
private ViewPager viewPager;
// a static variable to get a reference of our application context
public static Context contextOfApplication;
public static Context getContextOfApplication()
{
return contextOfApplication;
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE)
!= PackageManager.PERMISSION_GRANTED) {
requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},1);
// MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE is an
// app-defined int constant
return;
}}
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
viewPager = (ViewPager) findViewById(R.id.container);
setupViewPager(viewPager);
tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(viewPager);
contextOfApplication = getApplicationContext();
}
private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(new ListSong(), "SONGS");
adapter.addFragment(new GridAlbum(), "ALBUMS");
viewPager.setAdapter(adapter);
}
class ViewPagerAdapter extends FragmentPagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
@Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
@Override
public int getCount() {
return mFragmentList.size();
}
public void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
@Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
}
ListSong.java 它是具有列表视图并显示歌曲的三个片段之一。
public class ListSong extends Fragment {
private ArrayList<Song> songList;
private ListView songView;
Context applicationContext = MainActivity.getContextOfApplication();
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.listsongs, container, false);
songView = (ListView)rootView.findViewById(R.id.songsList);
songList = new ArrayList<Song>();
getSongList();
SongAdapter songAdt = new SongAdapter(getActivity(), songList);
songView.setAdapter(songAdt);
return rootView;
}
public void getSongList(){
ContentResolver musicResolver = applicationContext.getContentResolver();
Uri musicUri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
Cursor musicCursor = musicResolver.query(musicUri, null, null, null, null);
if(musicCursor!=null && musicCursor.moveToFirst()){
//get columns
int titleColumn = musicCursor.getColumnIndex
(android.provider.MediaStore.Audio.Media.TITLE);
int idColumn = musicCursor.getColumnIndex
(android.provider.MediaStore.Audio.Media._ID);
int artistColumn = musicCursor.getColumnIndex
(android.provider.MediaStore.Audio.Media.ARTIST);
//add songs to list
do {
long thisId = musicCursor.getLong(idColumn);
String thisTitle = musicCursor.getString(titleColumn);
String thisArtist = musicCursor.getString(artistColumn);
songList.add(new Song(thisId, thisTitle, thisArtist));
}
while (musicCursor.moveToNext());
}
}
}
这是我的错误日志。
1/data/app/com.example.adityaverma.practicemusic-2/split_lib_slice_9_apk.apk
10-18 13:18:41.254 22970-22970/com.example.adityaverma.practicemusic I/art: jiangtaottt OpenDexFilesFromOat open_oat_file.get() == nullptr 3 /data/dalvik-cache/arm64/data@app@com.example.adityaverma.practicemusic-2@split_lib_slice_9_apk.apk@classes.dex /data/app/com.example.adityaverma.practicemusic-2/split_lib_slice_9_apk.apk
10-18 13:18:41.254 22970-22970/com.example.adityaverma.practicemusic E/System: elements.add : /data/app/com.example.adityaverma.practicemusic-2/split_lib_slice_9_apk.apk /data/app/com.example.adityaverma.practicemusic-2/split_lib_slice_9_apk.apk /data/app/com.example.adityaverma.practicemusic-2/split_lib_slice_9_apk.apk
10-18 13:18:41.263 22970-22970/com.example.adityaverma.practicemusic I/InstantRun: starting instant run server: is main process
10-18 13:18:41.452 22970-22970/com.example.adityaverma.practicemusic W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
10-18 13:18:41.472 22970-22989/com.example.adityaverma.practicemusic W/art: Suspending all threads took: 9.127ms
10-18 13:18:41.476 22970-22989/com.example.adityaverma.practicemusic I/art: Background sticky concurrent mark sweep GC freed 2354(280KB) AllocSpace objects, 0(0B) LOS objects, 17% free, 951KB/1154KB, paused 10.617ms total 58.260ms
10-18 13:18:41.483 22970-22989/com.example.adityaverma.practicemusic W/art: Suspending all threads took: 6.912ms
10-18 13:18:41.520 22970-22970/com.example.adityaverma.practicemusic D/wangcy9: setStatusIcon occur wrong theme!
10-18 13:18:41.568 22970-22989/com.example.adityaverma.practicemusic W/art: Suspending all threads took: 6.977ms
10-18 13:18:41.572 22970-22989/com.example.adityaverma.practicemusic I/art: Background partial concurrent mark sweep GC freed 875(282KB) AllocSpace objects, 0(0B) LOS objects, 47% free, 1149KB/2MB, paused 8.290ms total 47.849ms
10-18 13:18:41.826 22970-22970/com.example.adityaverma.practicemusic I/ViewRootImpl: CPU Rendering VSync enable = true
10-18 13:18:41.829 22970-23142/com.example.adityaverma.practicemusic D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
10-18 13:18:41.837 22970-22970/com.example.adityaverma.practicemusic D/Atlas: Validating map...
10-18 13:18:41.909 22970-22970/com.example.adityaverma.practicemusic D/AndroidRuntime: Shutting down VM
10-18 13:18:41.913 22970-22970/com.example.adityaverma.practicemusic E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.adityaverma.practicemusic, PID: 22970
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.ContentResolver android.content.Context.getContentResolver()' on a null object reference
at com.example.adityaverma.practicemusic.ListSong.getSongList(ListSong.java:44)
at com.example.adityaverma.practicemusic.ListSong.onCreateView(ListSong.java:34)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2239)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1332)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1574)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1641)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:794)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2415)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2200)
at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2153)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:2034)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:651)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1239)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1087)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1613)
at android.view.View.measure(View.java:17565)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5545)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:713)
at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90)
at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1389)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:783)
at android.view.View.measure(View.java:17565)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5545)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:17565)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5545)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17565)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5545)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.view.View.measure(View.java:17565)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5545)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17565)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5545)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2652)
at android.view.View.measure(View.java:17565)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2030)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1185)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1392)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1073)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5906)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:828)
at android.view.Choreographer.doCallbacks(Choreographer.ja
10-18 13:19:00.841 22970-22970/? I/Process: Sending signal. PID: 22970 SIG: 9
答案 0 :(得分：0)
在ListSong课程中 - ＆gt; getSongList()方法，请指定以下代码行：
ContentResolver musicResolver = getActivity().getContentResolver();
而不是
ContentResolver musicResolver = applicationContext.getContentResolver();