我在使用光标时得到nullpointer异常。在这一点上感到困惑，因为我相信每个片段都在一个活动中，我在google中提到了一些点，我得到了这个异常，而我的片段实例不是附加到Activity。（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我的片段中，我在这里使用SWIPABLE视图）。 提前谢谢...
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;
}
这是我的logcat
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)
答案 0 :(得分：0)
我认为你必须初始化游标，然后从游标中获取任何东西，
你可以直接`getActivity（）。getContentResolver（）。试试这个，
如果它不起作用，则显示Log cat。
答案 1 :(得分：0)
我解决了这个问题...将异常发生部分移动到onAttach使用了上下文对象。更多参考检查下面的代码
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;
}
答案 2 :(得分：0)
尝试在实例化Fragment时从活动传递上下文，并使用此上下文而不是getActivity（）函数。
答案 3 :(得分：0)
java.lang.NullPointerException at com.bq.bqgdrive.DeviceTab.getFilePaths(DeviceTab.java:185) at com.bq.bqgdrive.DeviceTab.<init>(DeviceTab.java:145)
构造函数或成员变量初始化<init>为时过早，无法调用getActivity()。该片段尚未附加到活动中。
将初始化和getFilePaths()电话移至fragment lifecycle中的onAttach()或更晚。