當應用暫停后，Android詢問findViewById時，Android返回NullPointerException

Question

每當我使用應用程序切換器或應用程序以任何其他方式暫停時，恢復該應用程序時，當我嘗試在片段中使用findViewById時，都會收到NullPointerException 。 嘗試使用getActivity（）或與Main活動相關的任何東西時，也會發生相同的情況。 我試過使用isAdded()檢查是否附加了片段，它返回true，但仍然給出錯誤。 （不管代碼看起來如何，我仍然需要清理它）

不包括所有不相關的類和方法（例如褻瀆類）。

MainActivity onStart方法（啟動活動）

@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（發生崩潰的崩潰，崩潰發生在第四行的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

所有與視圖相關的代碼都必須移至onCreateView（）。 因此，只需將代碼放置在onCreateView（如果有片段的情況下）和onCreate（如果有活動的話）。

有關更多信息，請訪問https://developer.android.com/guide/components/fragments.html

Answer 2

由於getView()崩潰。 因為它無法獲取視圖。

你需要通過view持有編號為的觀點R.id.fabSendImage並嘗試調用view.findViewById(R.id.fabSendImage)來初始化。