列表视图中数组适配器的空指针异常。 ANDROID

Question

我有一个主视图（listview）和第二个主视图（edittext）。我使用 startActivityforResult() 将数据从第二个主视图向后传递到第一个主视图。我已经对其进行了测试，并且毫无问题地收到了字符串。但是，在列表视图中显示它存在一些问题。我的列表视图有两个 xml 文件，一个用于列表视图布局，一个用于文本视图行。我不知道为什么会出现空指针异常。

03-14 22:50:33.429    9268-9268/com.example.anusha.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.anusha.app, PID: 9268
java.lang.NullPointerException
        at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:392)
        at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
        at android.widget.AbsListView.obtainView(AbsListView.java:2780)
        at android.widget.ListView.measureHeightOfChildren(ListView.java:1274)
        at android.widget.ListView.onMeasure(ListView.java:1186)
        at android.view.View.measure(View.java:17594)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5398)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1410)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
        at android.view.View.measure(View.java:17594)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5398)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:17594)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5398)
        at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:453)
        at android.view.View.measure(View.java:17594)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5398)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:17594)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5398)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1410)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
        at android.view.View.measure(View.java:17594)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5398)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2588)
        at android.view.View.measure(View.java:17594)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2308)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2030)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1267)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6640)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:813)
        at android.view.Choreographer.doCallbacks(Choreographer.java:613)
        at android.view.Choreographer.doFrame(Choreographer.java:583)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:799)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:146)
        at android.app.ActivityThread.main(ActivityThread.java:5635)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
        at dalvik.system.NativeStart.main(Native Method)

这是我的列表视图的第一个主视图。我很确定问题出在数组适配器上。虽然不知道是什么。

 ArrayList<String> array= new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_address_list);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.activity_address_list,R.id.rowTextView, array);
    ListView listview = (ListView) findViewById(R.id.listView);
    listview.setAdapter(adapter);



}
private void Add() {
    Intent intent = new Intent(AddressList.this, SilentGeofence.class);
    startActivityForResult(intent, 2);

}

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == 2) {
        if (resultCode == RESULT_OK){
            String result = data.getStringExtra("result");
            array.add(result);


        }
    }
    }

这是我的第二个主要

   Button add = (Button) findViewById(R.id.button);
    add.setOnClickListener(new View.OnClickListener() {

        public void onClick(View view) {

            String ag = txt1.getText().toString().trim();
                txt1.setText("");
                Intent returnIntent = new Intent();
                returnIntent.putExtra("result",ag);
                setResult(RESULT_OK,returnIntent);
                finish();

Answer 1

您必须在 onCreate() 中初始化列表，就在 getSupportActionBar().setDisplayHomeAsUpEnabled(true);

之后

并且您的 ArrayAdapter<String> adapter 应该是一个字段而不是局部变量，因为在您执行 array.add(result) 之后，您还必须调用 adapter.notifyDataSetChanged() 以刷新并填充列表视图中的结果

Answer 2

public ArrayAdapter（上下文上下文，int 资源，int textViewResourceId，T[] 对象）

已添加到 API 级别 1 构造函数

参数 context 当前上下文。 resource 布局文件的资源 ID，其中包含实例化视图时要使用的布局。 textViewResourceId 要填充的布局资源中 TextView 的 id objects 要在 ListView 中表示的对象。

所以你应该使用 textview 的布局而不是 listview 布局见这里 see here

    new ArrayAdapter<>(this, R.layout.layout_name_of_the_xml_containing_textview,R.id.rowTextView, array);

列表视图中数组适配器的空指针异常。 ANDROID

NULL POINTER EXCEPTION for arrayadapter in listview. ANDROID

java

arrays

android

listview

nullpointerexception