Android 调用getActivity（）.getApplicationContext（）时片段类内出现Nullpointer异常
我在这里使用光标时遇到空指针异常。此时我感到困惑，因为我相信每个片段都在一个活动中，并且我在google中引用了一些观点，从中我发现当我的片段实例未连接到该活动时，会发生此异常。我的程序是从gallery中获取所有图像，并将其作为网格视图列在片段中，我在这里使用可滑动视图。 提前谢谢Android 调用getActivity（）.getApplicationContext（）时片段类内出现Nullpointer异常,android,sqlite,gridview,android-fragments,views,Android,Sqlite,Gridview,Android Fragments,Views,我在这里使用光标时遇到空指针异常。此时我感到困惑，因为我相信每个片段都在一个活动中，并且我在google中引用了一些观点，从中我发现当我的片段实例未连接到该活动时，会发生此异常。我的程序是从gallery中获取所有图像，并将其作为网格视图列在片段中，我在这里使用可滑动视图。 提前谢谢 public ArrayList<String> getFilePaths() { // android.provider.MediaStore.Images.Media
public ArrayList<String> getFilePaths()
{
// android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI
// android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI
Uri u =MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
System.out.println("uri is"+u);
String[] projection = { MediaStore.Images.Media.DATA };
// {MediaStore.Images.ImageColumns.DATA};
// { MediaStore.Images.Media.DATA };
Cursor c = null;
//treeset in which images are sorted in ascending order
SortedSet<String> dirList = new TreeSet<String>();
ArrayList<String> resultIAV = new ArrayList<String>();
String[] directories = null;
if ((u != null) &&(projection!=null))
{
System.out.println("projection is"+projection);
//null pointer exception
// Cursor cursor = getContentResolver().query(selectedImage,
// filePathColumn, null, null, null);
//getContentResolver().
Log.e("devicetab","cursor not equalto null");
Log.e("devicetab",getActivity().getApplicationContext().toString());
//not executing this line
//getSupportLoadManager().initLoader(0, null, getActivity());
// c=getSupportLoaderManager.(u, projection,null,null,null);
System.out.println("context "+getActivity().getApplicationContext());
System.out.println("activity"+getActivity());
c =getActivity().getApplicationContext().getContentResolver().query(u, projection, null, null, null);
// c =getActivity().getContentResolver().query(u, projection,null,null,null);
getActivity().startManagingCursor(c);
c.moveToFirst();
Log.e("devicetab","cursor");
}
if ((c != null) && (c.moveToFirst()))
{
do
{
String tempDir = c.getString(0);
tempDir = tempDir.substring(0, tempDir.lastIndexOf("/"));
try{
dirList.add(tempDir);
}
catch(Exception e)
{
}
}
while (c.moveToNext());
//string array driectories
directories = new String[dirList.size()];
dirList.toArray(directories);
}
// c.close();
for(int i=0;i<dirList.size();i++)
{
File imageDir = new File(directories[i]);
File[] imageList = imageDir.listFiles();
// File targetDirector = new File(picturePath);
// Log.e("Devicetab","before files");
// File[] files = targetDirector.listFiles();
if(imageList == null)
continue;
for (File imagePath : imageList) {
try {
if(imagePath.isDirectory())
{
imageList = imagePath.listFiles();
}
if ( imagePath.getName().contains(".jpg")|| imagePath.getName().contains(".JPG")
|| imagePath.getName().contains(".jpeg")|| imagePath.getName().contains(".JPEG")
|| imagePath.getName().contains(".png") || imagePath.getName().contains(".PNG")
|| imagePath.getName().contains(".gif") || imagePath.getName().contains(".GIF")
|| imagePath.getName().contains(".bmp") || imagePath.getName().contains(".BMP")
)
{
String path= imagePath.getAbsolutePath();
resultIAV.add(path);
}
}
// }
catch (Exception e) {
e.printStackTrace();
}
}
}
return resultIAV;
}
11-05 05:19:25.659: W/TabsPagerAdapter(9498): inside class2 fragmentmanager
11-05 05:19:25.689: E/Bqswipeview(9498): inside onTabSelected
11-05 05:19:25.689: E/Bqswipeview(9498): tabs added
11-05 05:19:26.269: W/TabsPagerAdapter(9498): inside class2 tabspageradapter
11-05 05:19:26.269: I/System.out(9498): uri iscontent://media/external/images/media
11-05 05:19:26.269: I/System.out(9498): projection is[Ljava.lang.String;@b1155080
11-05 05:19:26.269: E/devicetab(9498): cursor not equalto null
11-05 05:19:26.269: D/AndroidRuntime(9498): Shutting down VM
11-05 05:19:26.269: W/dalvikvm(9498): threadid=1: thread exiting with uncaught exception (group=0xb0d13b20)
11-05 05:19:26.269: E/AndroidRuntime(9498): FATAL EXCEPTION: main
11-05 05:19:26.269: E/AndroidRuntime(9498): Process: com.bq.bqgdrive, PID: 9498
11-05 05:19:26.269: E/AndroidRuntime(9498): java.lang.NullPointerException
11-05 05:19:26.269: E/AndroidRuntime(9498): at com.bq.bqgdrive.DeviceTab.getFilePaths(DeviceTab.java:185)
11-05 05:19:26.269: E/AndroidRuntime(9498): at com.bq.bqgdrive.DeviceTab.<init>(DeviceTab.java:145)
11-05 05:19:26.269: E/AndroidRuntime(9498): at com.bq.tabsswipe.adapter.TabsPagerAdapter.getItem(TabsPagerAdapter.java:28)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:97)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:837)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.support.v4.view.ViewPager.populate(ViewPager.java:987)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.View.measure(View.java:16497)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.View.measure(View.java:16497)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
11-05 05:19:26.269: E/AndroidRuntime(9498): at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.View.measure(View.java:16497)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
11-05 05:19:26.269: E/AndroidRuntime(9498): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.View.measure(View.java:16497)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.Choreographer.doCallbacks(Choreographer.java:574)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.Choreographer.doFrame(Choreographer.java:544)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.os.Handler.handleCallback(Handler.java:733)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.os.Handler.dispatchMessage(Handler.java:95)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.os.Looper.loop(Looper.java:136)
11-05 05:19:26.269: E/AndroidRuntime(9498): at android.app.ActivityThread.main(ActivityThread.java:5017)
11-05 05:19:26.269: E/AndroidRuntime(9498): at java.lang.reflect.Method.invokeNative(Native Method)
11-05 05:19:26.269: E/AndroidRuntime(9498): at java.lang.reflect.Method.invoke(Method.java:515)
11-05 05:19:26.269: E/AndroidRuntime(9498): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
11-05 05:19:26.269: E/AndroidRuntime(9498): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
11-05 05:19:26.269: E/AndroidRuntime(9498): at dalvik.system.NativeStart.main(Native Method)
我想你必须初始化游标，然后从游标得到任何东西 您可以直接使用`getActivity.getContentResolver。试试这个
如果不起作用，则显示日志cat。我解决了此问题…将异常发生部分移动到使用上下文对象的onAttach。有关更多参考信息，请查看下面的代码
ImageAdapter myImageAdapter;
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
activity.setContentView(R.layout.devicetab);
Log.e("Devicetab","onCreate ");
GridView gridview = (GridView) activity.findViewById(R.id.gridView1);
//myImageAdapter=new ImageAdapter(this);
ArrayList<String> arrlist=getFilePaths(activity.getApplicationContext());
Iterator<String> itr=arrlist.iterator();
myImageAdapter = new ImageAdapter(activity.getApplicationContext());
do
{
String obj=itr.next();
// setAdapter(obj);
myImageAdapter.add(obj);
}
while(itr.hasNext());
gridview.setAdapter(myImageAdapter);
}
public ArrayList<String> getFilePaths(Context cntx)
{
Uri u =MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
System.out.println("uri is"+u);
String[] projection = { MediaStore.Images.Media.DATA };
Cursor c = null;
//treeset in which images are sorted in ascending order
SortedSet<String> dirList = new TreeSet<String>();
ArrayList<String> resultIAV = new ArrayList<String>();
String[] directories = null;
if ((u != null) &&(projection!=null))
{
System.out.println("projection is"+projection);
Log.e("devicetab","cursor not equalto null");
//System.out.println("context "+getActivity().getApplicationContext());
//here null pointer occurs
c =cntx.getContentResolver().query(u, projection, null, null, null);
getActivity().startManagingCursor(c);
c.moveToFirst();
Log.e("devicetab","cursor");
}
if ((c != null) && (c.moveToFirst()))
{
do
{
String tempDir = c.getString(0);
tempDir = tempDir.substring(0, tempDir.lastIndexOf("/"));
try{
dirList.add(tempDir);
}
catch(Exception e)
{
}
}
while (c.moveToNext());
//string array driectories
directories = new String[dirList.size()];
dirList.toArray(directories);
}
for(int i=0;i<dirList.size();i++)
{
File imageDir = new File(directories[i]);
File[] imageList = imageDir.listFiles();
if(imageList == null)
continue;
for (File imagePath : imageList) {
try {
if(imagePath.isDirectory())
{
imageList = imagePath.listFiles();
}
if ( imagePath.getName().contains(".jpg")|| imagePath.getName().contains(".JPG")
|| imagePath.getName().contains(".jpeg")|| imagePath.getName().contains(".JPEG")
|| imagePath.getName().contains(".png") || imagePath.getName().contains(".PNG")
|| imagePath.getName().contains(".gif") || imagePath.getName().contains(".GIF")
|| imagePath.getName().contains(".bmp") || imagePath.getName().contains(".BMP")
)
{
String path= imagePath.getAbsolutePath();
resultIAV.add(path);
}
}
catch (Exception e) {
e.printStackTrace();
}
}
}
return resultIAV;
}
尝试在实例化片段时从活动传递上下文，并使用此上下文而不是getActivity函数 构造函数或成员变量初始化太早，无法调用getActivity。该片段尚未附加到活动
将初始化和GetFilePath调用移动到onAttach或更高版本中。您能给我们看一下logcat吗？我在问题下给出了我的logcat，请检查..下面是logcat…我不知道这是给出logcat的正确方式。这不是显示任何数据的正确方式，请编辑您的问题，你把Log cat放在答案中，但这不是答案。下次其他wise堆栈溢出将不允许再次提问时请小心。哦，抱歉。我将检查put mylogcatFragments不应具有接受args的构造函数。是的，我将initialization和GetFilePath方法移动到了onAttach，但它不会工作相同的异常情况发生…之前我使用了onCreateBundle savedInstanceState而不是onAttach
java.lang.NullPointerException
at com.bq.bqgdrive.DeviceTab.getFilePaths(DeviceTab.java:185)
at com.bq.bqgdrive.DeviceTab.<init>(DeviceTab.java:145)