Android 在应用程序暂停后询问 findViewById 时返回 NullPointerException

Question

每当我使用应用程序切换器或应用程序以任何其他方式暂停时，在恢复它时，我在尝试在我的片段中使用findViewById时会得到NullPointerException。当尝试使用 getActivity() 或与 Main 活动相关的任何内容时也会发生同样的情况。我尝试检查片段是否附加isAdded()它返回 true，但仍然给出错误。(不介意代码的外观，我仍然需要清理它)

不包括所有不相关的类和方法(例如亵渎类)。

启动方法(启动活动)

@Override
public void onStart() {
super.onStart();
Profanity.downloadList();
if (AskForPermissions()) {
if (mAuth.getCurrentUser() != null) {
mAuth.getCurrentUser().reload().addOnFailureListener(new OnFailureListener() {
@Override
public void onFailure(@NonNull Exception e) {
FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.MainFragment, new LoginFragment()).commit();
}
}).addOnSuccessListener(new OnSuccessListener<Void>() {
@Override
public void onSuccess(Void aVoid) {
FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.MainFragment, new HomeFragment()).commit();
}
});
} else {
FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.MainFragment, new LoginFragment()).commit();
}
} else {
onStart();
}
}

HomeFragment(崩溃的那个，崩溃发生在第 4 行的 Started() 下)

@SuppressWarnings("all")
@Override
public void onStart() {
super.onStart();
loadVariables();
final String UUID = ((MainActivity) getActivity()).mAuth.getCurrentUser().getUid();
User.UUID = UUID;
if (User.userName == null || User.userName.equals("")) {
Functions.loadUserData(UUID).addOnCompleteListener(new OnCompleteListener() {
@Override
public void onComplete(@NonNull Task task) {
if (task.getResult() == null) {
final AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setTitle("Choose your username");
final EditText input = new EditText(getActivity());
input.setInputType(InputType.TYPE_CLASS_TEXT);
builder.setView(input);
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
}
});
final AlertDialog dialog = builder.create();
dialog.show();
dialog.getButton(AlertDialog.BUTTON_POSITIVE).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (input.getText() != null && !input.getText().toString().equals("") && !input.getText().toString().equals(" ")) {
if (input.getText().toString().toCharArray().length > 16) {
dialog.dismiss();
Functions.showBottomMessage(getView(), "Your username must be maximum 16 characters.");
dialog.show();
} else if (Profanity.contains(input.getText().toString())) {
dialog.dismiss();
Functions.showBottomMessage(getView(), "Please refrain from using restricted words in your username.");
input.setText("");
dialog.show();
} else {
User.userName = input.getText().toString();
dialog.dismiss();
FirebaseReferences.users.child(User.UUID).child("name").setValue(User.userName);
Functions.showBottomMessage(getView(), "Username saved.");
}
} else {
dialog.dismiss();
Functions.showBottomMessage(getView(), "Please enter a valid username.");
dialog.show();
}
}
});
Started();
} else {
HashMap temp = (HashMap) task.getResult();
if (temp.containsKey("name")) {
User.userName = temp.get("name").toString();
} else {
final AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setTitle("Choose your username");
final EditText input = new EditText(getActivity());
input.setInputType(InputType.TYPE_CLASS_TEXT);
builder.setView(input);
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
}
});
final AlertDialog dialog = builder.create();
dialog.show();
dialog.getButton(AlertDialog.BUTTON_POSITIVE).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (input.getText() != null && !input.getText().toString().equals("") && !input.getText().toString().equals(" ")) {
User.userName = input.getText().toString();
dialog.dismiss();
FirebaseReferences.users.child(UUID).child("name").setValue(input.getText().toString());
} else {
dialog.dismiss();
dialog.show();
}
}
});
}
if (temp.containsKey("place")) {
User.place = temp.get("place").toString();
}
if (temp.containsKey("ratedImages")) {
User.ratedImages = (ArrayList<String>) temp.get("ratedImages");
}
if (temp.containsKey("developer")) {
if (Boolean.valueOf(temp.get("developer").toString().toLowerCase()))
User.isDeveloper = true;
}
Started();
}
}
});
} else {
Started();
}
}
@SuppressWarnings("all")
private void Started() {
mainImageProgressBar.setVisibility(View.VISIBLE);
secondaryImageProgressBar.setVisibility(View.VISIBLE);
CacheHandler.update(getActivity(), imageView, secondImageView, true);
/*THIS IS THE FIRST CRASH POINT - */getView().findViewById(R.id.fabSendImage).setOnClickListener(getBtnSendImageOnClickListener());
getView().findViewById(R.id.btnReportImage).setOnClickListener(btnReportImageOnClick);
}

Answer 1

所有与视图相关的代码都必须移动到onCreateView()。因此，只需将您的代码放在 onCreateView 中(如果出现片段)和 onCreate (如果发生活动)。

有关更多信息，请浏览 https://developer.android.com/guide/components/fragments.html

Answer 2

由于getView()而崩溃。因为它无法获得视图。

您需要传递保存 id 为R.id.fabSendImage的视图的view，并尝试调用view.findViewById(R.id.fabSendImage)进行初始化。