我有一个片段(F1)与这样的公共方法
public void asd() {
if (getActivity() == null) {
Log.d("yes","it is null");
}
}
是的,当我调用它(从活动),它是空…
FragmentTransaction transaction1 = getSupportFragmentManager().beginTransaction();
F1 f1 = new F1();
transaction1.replace(R.id.upperPart, f1);
transaction1.commit();
f1.asd();
一定是我做错了什么,但我不知道是什么。
PJL是对的。
我采纳了他的建议,我是这样做的:
为fragment定义的全局变量:
attachingActivityLock = new Object();
private boolean syncVariable = false;
实现
@Override
onAttach(Activity Activity) {
super.onAttach(活动);
synchronized (attachingActivityLock) {
syncVariable = true;
attachingActivityLock.notifyAll ();
}
}
3.我在线程中包装了我的函数,在那里我需要调用getActivity(),因为如果它将在主线程上运行,我将用步骤4阻塞线程。onAttach()将永远不会被调用。
Thread processImage = new Thread(new Runnable() {
@Override
public void run() {
processImage();
}
});
processImage.start();
4所示。在我的函数中,我需要调用getActivity(),我使用这个(在调用getActivity()之前)
synchronized (attachingActivityLock) {
while(!syncVariable){
try {
attachingActivityLock.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
如果你有一些UI更新,记得在UI线程上运行它们。我需要更新ImgeView,所以我做了:
image.post(new Runnable() {
@Override
public void run() {
image.setImageBitmap(imageToShow);
}
});
编写一个通用方法,确保永远不会得到空Activity。
public class BaseFragment extends Fragment {
private Context contextNullSafe;
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
/*View creation related to this fragment is finished here. So in case if contextNullSafe is null
* then we can populate it here.In some discussion in - https://stackoverflow.com/questions/6215239/getactivity-returns-null-in-fragment-function
* and https://stackoverflow.com/questions/47987649/why-getcontext-in-fragment-sometimes-returns-null,
* there are some recommendations to call getContext() or getActivity() after onCreateView() and
* onViewCreated() is called after the onCreateView() call every time */
if (contextNullSafe == null) getContextNullSafety();
}
@Override
public void onAttach(@NonNull Context context) {
super.onAttach(context);
contextNullSafe = context;
}
/**CALL THIS IF YOU NEED CONTEXT*/
public Context getContextNullSafety() {
if (getContext() != null) return getContext();
if (getActivity() != null) return getActivity();
if (contextNullSafe != null) return contextNullSafe;
if (getView() != null && getView().getContext() != null) return getView().getContext();
if (requireContext() != null) return requireContext();
if (requireActivity() != null) return requireActivity();
if (requireView() != null && requireView().getContext() != null)
return requireView().getContext();
return null;
}
/**CALL THIS IF YOU NEED ACTIVITY*/
public FragmentActivity getActivityNullSafety() {
if (getContextNullSafety() != null && getContextNullSafety() instanceof FragmentActivity) {
/*It is observed that if context it not null then it will be
* the related host/container activity always*/
return (FragmentActivity) getContextNullSafety();
}
return null;
}