android - Id 是正确的，但是 - java.lang.NullPointerException: android.widget.TextView.setText(java.lang.CharSequence)' 在空对象引用上

问题描述

我在 setText() 的 NPE 上遇到了这么长时间的麻烦。
Tab1Fragment 中的一些状态，我可以通过以下代码看到：

文本视图为空。
fullText 获得了理想的价值。

我错过了什么吗？我唯一的目的是在点击时从 HomeFragment 中的 listView 更新 Tab1Fragment 中的 TextView。（这似乎遥遥领先于我）
提前谢谢。

HomeFragment.java

public class HomeListAdapter extends BaseAdapter {
        AddLawMap addLawMap = new AddLawMap();
        private final ArrayList<String> list;
        private Tab1Fragment tab1Fragment = new Tab1Fragment();
        private Tab2Fragment tab2Fragment = new Tab2Fragment();
        private Tab3Fragment tab3Fragment = new Tab3Fragment();
        private GetTextFragment getTextFragment = new GetTextFragment();

...

@Override
        public View getView(int position, View convertView, ViewGroup parent){
            final View result;

            if(convertView == null){
                result = LayoutInflater.from(parent.getContext()).inflate(R.layout.home_item, parent, false);
            }else{
                result = convertView;
            }

            if(getCount() != 0) {

                String itemId = getItem(position);
                final TextView tv1 = result.findViewById(R.id.text_home_item);
                tv1.setTag(itemId);
                tv1.setText(addLawMap.getMapString().get(itemId));

                result.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(final View view) {
                        final String tag = tv1.getTag().toString();

                        AlertDialog.Builder builder2 = new AlertDialog.Builder(mcontext);
                        builder2.setTitle(R.string.choose_fragment)
                                .setItems(R.array.choose_fragment, new DialogInterface.OnClickListener() {
                                    @Override
                                    public void onClick(DialogInterface dialog, int which) {
                                        int duration = Toast.LENGTH_SHORT;
                                        Toast toast = Toast.makeText(mcontext, R.string.after_set_fulltext_toast, duration);

                                        switch (which) {
                                            case 0:
                                                tab1Fragment.setFullText(getTextFragment.getFileStream(tag));
                                                tab1Fragment.updateUi();
                                                toast.show();

                                                break;
                                            ...
                                        }
                                    }
                                });
                        AlertDialog dialog2 = builder2.create();
                        dialog2.show();
                    }
                });
                return result;

            }else {
                return result;
            }
        }
    }

Tab1Fragment.java

public class Tab1Fragment extends Fragment {

    private static final String ARG_COUNT = "param1";
    private Integer counter;
    private Handler mHandler = new Handler(Looper.getMainLooper());
    private String fullText;
    private int numSetText;
    private int numTab1;
    @NonNull TextView textView;


    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        Log.i("TAB1_FRAGMENT", "/onAttach");
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            counter = getArguments().getInt(ARG_COUNT);
        }
         numTab1 = 0;
         numSetText = 0;
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @NonNull ViewGroup container, Bundle savedInstanceState){
        super.onCreateView(inflater, container, savedInstanceState);
        Log.i("TAB1_FRAGMENT", "/onCreateView");

        return inflater.inflate(R.layout.fragment_tab1, container, false);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState){
        super.onViewCreated(view, savedInstanceState);
        TextView textView = (TextView) getView().findViewById(R.id.tab1_textview);

        if(fullText == null){
            ImageView imageView = (ImageView) getView().findViewById(R.id.none_added);
            imageView.setVisibility(View.VISIBLE);
            textView.setVisibility(View.INVISIBLE);
        }else{
            textView.setText(fullText);
        }
        Log.i("TAB1_FRAGMENT", "/onViewCreated");
    }

    public void setFullText(String fullText){
        this.fullText = fullText;
        Log.i("TAB1_FRAGMENT", "/setFullText()");
        ++ numSetText;
    }

    public void updateUi(){
        if(fullText != null){
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    textView.setText(fullText);
                    ++numTab1;
                }
            });
        }
    }



    @Override
    public void onPause() {
        super.onPause();
        Log.i("TAB1_FRAGMENT", "/onPause");
    }

    @Override
    public void onStart(){
        super.onStart();
        Log.i("TAB1_FRAGMENT", "/onStart");
    }

    @Override
    public void onResume(){
        super.onResume();
        Log.i("TAB1_FRAGMENT", "/onResume");

    }

    @Override
    public void onDetach(){
        super.onDetach();
        mHandler = null;
    }

fragment_tab1.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/none_added"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:src="@drawable/tab_none_added"
        android:visibility="gone"/>

        <TextView
            android:id="@+id/tab1_textview"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:lineSpacingExtra="3dp"/>

</LinearLayout>

日志猫

2020-06-08 22:52:25.855 9668-9668/com.example.morina.mylaw I/TAB1_FRAGMENT: /setFullText()
2020-06-08 22:52:25.881 9668-9668/com.example.morina.mylaw W/InputEventReceiver: Attempted to finish an input event but the input event receiver has already been disposed.
2020-06-08 22:52:25.882 9668-9668/com.example.morina.mylaw E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.morina.mylaw, PID: 9668
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at com.example.morina.mylaw.Tab1Fragment$1.run(Tab1Fragment.java:82)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

标签： androidandroid-fragments

android - Id 是正确的，但是 - java.lang.NullPointerException: android.widget.TextView.setText(java.lang.CharSequence)' 在空对象引用上

问题描述

解决方案

推荐阅读