我有一个使用popupWindow进行用户聊天的应用程序。它是从Fragment启动的，提供的context是getActivity()。我将输入popupWindow的multilineEditText，大约5分钟后，我将不断地得到一个崩溃和以下错误：

android.view.WindowManager$BadTokenException: Unable to add window -- token android.view.ViewRootImpl$W@d1cf1ec is not valid; is your activity running?
    at android.view.ViewRootImpl.setView(ViewRootImpl.java:1147)
    at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:471)
    at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:95)
    at android.widget.PopupWindow.invokePopup(PopupWindow.java:1621)
    at android.widget.PopupWindow.showAtLocation(PopupWindow.java:1375)
    at android.widget.PopupWindow.showAtLocation(PopupWindow.java:1341)
    at android.widget.Editor$PinnedPopupWindow.updatePosition(Editor.java:3817)
    at android.widget.Editor$PinnedPopupWindow.show(Editor.java:3773)
    at android.widget.Editor$SuggestionsPopupWindow.show(Editor.java:4287)
    at android.widget.Editor.replace(Editor.java:587)
    at android.widget.-$$Lambda$DZXn7FbDDFyBvNjI-iG9_hfa7kw.run(Unknown Source:2)
    at android.os.Handler.handleCallback(Handler.java:883)
    at android.os.Handler.dispatchMessage(Handler.java:100)
    at android.os.Looper.loop(Looper.java:237)
    at android.app.ActivityThread.main(ActivityThread.java:8167)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:496)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100)

我知道这对解释错误没有太大帮助，但是，就我所知，这是getActivity返回null的问题，而我的popupWindow由于缺少context而强制分离。有什么方法可以避免和/或修复这个问题吗？
下面是一些示例代码，可帮助您可视化popupWindow问题：

if(getActivity() != null) {

        //Retrieve layout inflater
        LayoutInflater layoutInflater = (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        if (layoutInflater != null) {

            //Inflate custom popup layout
            View inflatedView = layoutInflater.inflate(R.layout.popup_chat_layout, null, false);

            writeMessageEditText = inflatedView.findViewById(R.id.writeMessageEditText);

            chatLayoutManager = new LinearLayoutManager(getActivity());
            //Read from bottom-up
            chatLayoutManager.setStackFromEnd(true);
            chatMessagesRecycler.setLayoutManager(chatLayoutManager);

            popupWindow = new PopupWindow(inflatedView, displayWidth, displayHeight, true);

            popupWindow.setAnimationStyle(R.style.PopupAnimation);

            popupWindow.setInputMethodMode(PopupWindow.INPUT_METHOD_NEEDED);
            popupWindow.setHeight(WindowManager.LayoutParams.MATCH_PARENT);

            popupWindow.showAtLocation(v, Gravity.BOTTOM, 0, 0);

            //Cap message lines - the purpose is not to cap characters, but ONLY to cap length
            writeMessageEditText.addTextChangedListener(new TextWatcher() {
                @Override
                public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                }

                @Override
                public void onTextChanged(CharSequence s, int start, int before, int count) {
                }

                @Override
                public void afterTextChanged(Editable s) {
                    if (writeMessageEditText.getLayout().getLineCount() > 150) {
                        if (writeMessageEditText.getText() != null) {
                            writeMessageEditText.getText().delete(writeMessageEditText.getText().length() - 1, writeMessageEditText.getText().length());
                        }
                        Toast.makeText(getActivity(), "Message may not exceed 150 lines", Toast.LENGTH_SHORT).show();
                    }
                }
            });

            //This was implemented during testing - possible to remove but fine for now
            dismissChatButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    resetAll();
                    previousChat = null;
                    if(popupWindow != null) {
                        popupWindow.dismiss();
                        popupWindow = null;
                    }
                }
            });

        }

    }