我使用扩展活动尝试了以下代码，但是现在我更改了代码以使用扩展片段。我在网上搜索并找到getActivity()函数来调用query()和其他函数。我尝试了这个，但现在它出错了：
错误
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.admin.funtube_mp4/com.example.admin.funtube_mp4.Main}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2404)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2464)
at android.app.ActivityThread.access$900(ActivityThread.java:172)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5653)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.admin.funtube_mp4.HomeFragmant.init_phone_video_grid(HomeFragmant.java:65)
at com.example.admin.funtube_mp4.HomeFragmant.onCreateView(HomeFragmant.java:49)
at android.app.Fragment.performCreateView(Fragment.java:1700)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:890)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
at android.app.BackStackRecord.run(BackStackRecord.java:684)
at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1453)
at android.app.Activity.performStart(Activity.java:5550)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2377)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2464)
at android.app.ActivityThread.access$900(ActivityThread.java:172)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5653)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
at dalvik.system.NativeStart.main(Native Method)
码
public class HomeFragmant extends Fragment{
private Cursor videocursor;
private int video_column_index;
ListView videolist;
List<String> listpath = new ArrayList<String>();
String[] paths=new String[100];
int count;
String[] thumbColumns = { MediaStore.Video.Thumbnails.DATA, MediaStore.Video.Thumbnails.VIDEO_ID };
String path;
File file;
public HomeFragmant() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_home, container, false);
videolist = (ListView) getActivity(). findViewById(R.id.PhoneVideoList);
init_phone_video_grid();
return rootView;
}
private void init_phone_video_grid() {
System.gc();
String[] proj = { MediaStore.Video.Media._ID, MediaStore.Video.Media.DATA, MediaStore.Video.Media.DISPLAY_NAME, MediaStore.Video.Media.SIZE };
// file = new File(Environment.getExternalStorageDirectory() + File.separator + "Funtube/UserData/Videos/");
// videocursor =getActivity().getContentResolver().query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, proj, MediaStore.Images.Media.DATA + " LIKE ? ", new String[]{"%" + file.getAbsolutePath().toString() + "%"}, null);
videocursor = getActivity().getContentResolver().query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI,proj, null, null, null);
// videocursor =getActivity().managedQuery(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, proj, MediaStore.Images.Media.DATA + " LIKE ? ", new String[]{"%" + file.getAbsolutePath().toString() + "%"}, null);
count = videocursor.getCount();
videolist.setAdapter(new VideoAdapter(getActivity().getApplicationContext()));
videolist.setOnItemClickListener(videogridlistener);
}
private AdapterView.OnItemClickListener videogridlistener = new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView parent, View v, int position,long id) {
System.gc();
video_column_index = videocursor.getColumnIndexOrThrow(MediaStore.Video.Media.DATA);
videocursor.moveToPosition(position);
String filename = videocursor.getString(video_column_index);
Intent intent = new Intent(getActivity(),ViewVideo.class);
intent.putExtra("videofilename", filename);
startActivity(intent);
}
};
public class VideoAdapter extends BaseAdapter {
private Context vContext;
public VideoAdapter(Context c) {
vContext = c;
}
public int getCount() {
return count;
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
System.gc();
ViewHolder holder;
String id = null;
convertView = null;
if (convertView == null) {
convertView = LayoutInflater.from(vContext).inflate(R.layout.listitem, parent, false);
holder = new ViewHolder();
holder.txtTitle = (TextView) convertView.findViewById(R.id.txtTitle);
holder.txtSize = (TextView) convertView.findViewById(R.id.txtSize);
holder.thumbImage = (ImageView) convertView.findViewById(R.id.imgIcon);
video_column_index = videocursor.getColumnIndexOrThrow(MediaStore.Video.Media.DISPLAY_NAME);
videocursor.moveToPosition(position);
id = videocursor.getString(video_column_index);
video_column_index = videocursor.getColumnIndexOrThrow(MediaStore.Video.Media.SIZE);
videocursor.moveToPosition(position);
// id += " Size(KB):" +
// videocursor.getString(video_column_index);
holder.txtTitle.setText(id);
holder.txtSize.setText(" Size(KB):"+ videocursor.getString(video_column_index));
String[] proj = { MediaStore.Video.Media._ID, MediaStore.Video.Media.DISPLAY_NAME, MediaStore.Video.Media.DATA };
@SuppressWarnings("deprecation")
Cursor cursor = getActivity().getContentResolver().query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, proj, MediaStore.Video.Media.DISPLAY_NAME + "=?", new String[]{id}, null);
cursor.moveToFirst();
long ids = cursor.getLong(cursor
.getColumnIndex(MediaStore.Video.Media._ID));
ContentResolver crThumb = getActivity().getContentResolver();
BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 1;
Bitmap curThumb = MediaStore.Video.Thumbnails.getThumbnail(
crThumb, ids, MediaStore.Video.Thumbnails.MICRO_KIND,
options);
holder.thumbImage.setImageBitmap(curThumb);
curThumb = null;
} /*
* else holder = (ViewHolder) convertView.getTag();
*/
return convertView;
}
}
static class ViewHolder {
TextView txtTitle;
TextView txtSize;
ImageView thumbImage;
}
}
答案 0 :(得分：1)
请勿在{{1}}中致电getActivity()，您无法保证onCreateView在那里完全创建。使用Activity方法获取对onActivityCreated。
除非您害怕泄露Activity，否则您只需使用Activity，无需检索ApplicationContext即可创建适配器恕我直言。
警告：如果在Fragment中需要Context对象，则可以 调用getActivity（）。但是，请注意只调用getActivity（） 当片段附加到活动时。当片段不是 尚未附着，或在其生命周期结束时被分离， getActivity（）将返回null。
答案 1 :(得分：0)
完全同意@ 2Dee，可能只需要尝试使用 getActivity（）
videolist.setAdapter(new VideoAdapter(getActivity()));