java - 使用ArrayAdapter填充ListView时无法找到TextView

Question

我在以下行收到空指针异常，就好像找不到我引用的 TextView:

                descriptor.setText("Single");

我检查了 ID 字段，它在代码和 XML 中完全相同，我不确定适配器中的其他地方是否有错误。

日志记录

06-02 23:24:08.903  11160-11160/com.example.albert.betterapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.albert.betterapp, PID: 11160
    java.lang.NullPointerException
            at com.example.albert.betterapp.DisplayAllBets$MyListAdapter.getView(DisplayAllBets.java:464)
            at android.widget.AbsListView.obtainView(AbsListView.java:2733)
            at android.widget.ListView.measureHeightOfChildren(ListView.java:1274)
            at android.widget.ListView.onMeasure(ListView.java:1186)
            at android.view.View.measure(View.java:17396)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365)
            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:17396)
            at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719)
            at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455)
            at android.view.View.measure(View.java:17396)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
            at android.view.View.measure(View.java:17396)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365)
            at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:444)
            at android.view.View.measure(View.java:17396)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.view.View.measure(View.java:17396)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365)
            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:17396)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2505)
            at android.view.View.measure(View.java:17396)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2175)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1316)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1513)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1200)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6401)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:803)
            at android.view.Choreographer.doCallbacks(Choreographer.java:603)
            at android.view.Choreographer.doFrame(Choreographer.java:573)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:789)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5335)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
            at dalvik.system.NativeStart.main(Native Method)

适配器

private class MyListAdapter extends ArrayAdapter<BetDisplayer> {
        public MyListAdapter() {
            super(DisplayAllBets.this,R.layout.activity_singletotalbet,listwriter);
        }
        @Override
        public View getView(int position,View convertView, ViewGroup parent) {
            View itemView = convertView;
            if (itemView == null) {
                itemView = getLayoutInflater().inflate(R.layout.activity_singletotalbet,parent,false);
            }
            BetDisplayer currentwriter = listwriter.get(position);
            Log.d("TESTING", currentwriter.getSelections());
            Log.d("TESTING2", currentwriter.getSelections());
            String selections = currentwriter.getSelections();
            int numberofselections = 0;
            for( int i=0; i<selections.length(); i++ ) {
                if( selections.charAt(i) == '/' ) {
                    numberofselections++;
                }
            }
            if (numberofselections == 1) {
                TextView descriptor = (TextView) findViewById(R.id.no);
                descriptor.setText("Single");
            } else if (numberofselections == 2) {
                TextView descriptor = (TextView) findViewById(R.id.no);
                descriptor.setText("Double");
            } else if (numberofselections == 3) {
                TextView descriptor = (TextView) findViewById(R.id.no);
                descriptor.setText("Treble");
            } else {
                TextView descriptor = (TextView) findViewById(R.id.no);
                descriptor.setText("Accumulator" + "(" + numberofselections + ")");
            }
            TextView status = (TextView) itemView.findViewById(R.id.status);
            status.setText(currentwriter.getStatus());
            return itemView;
        }
    }
    private void PopulateList() {
        ArrayAdapter<BetDisplayer> adapter = new MyListAdapter();
        final ListView list = (ListView) findViewById(R.id.betslistviews);
        list.setAdapter(adapter);
    }

            }

Answer 1

因为，TextView描述符是itemView的一部分(来自R.layout.activity_singletotalbet)，所以使用itemView<的引用进行访问

喜欢，

TextView descriptor = (TextView) itemView.findViewById(R.id.no);