Question

我搜索了其他主题并得出结论，我的listview是空指针异常的原因，但我无论如何都无法修复它。

这是我的XML文件

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

<ListView
    android:id="@+id/instantme_check_list"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:layout_weight="2.88" >
</ListView>

将剩下的部分排除在外，以减少杂乱，我的代码是

public class instantme_check extends Activity {
  InputStream is = null;
  TextView name;
  TextView content;
  EditText entername;
  EditText entercontent;
  private ListView list;
      ...

  name = (TextView) findViewById(R.id.instantme_check_name);
  content = (TextView) findViewById(R.id.instantme_check_message);
  entername = (EditText) findViewById(R.id.instantme_check_entername);
  entercontent = (EditText) findViewById(R.id.instantme_check_entermessage);
  list = (ListView) findViewById(R.id.instantme_check_list);
      ...

  listAdapter4 = new displayadapter4();
  list.setAdapter(listAdapter4);

至于显示适配器类（我已经在代码的其他两个部分使用它，它工作，所以我认为它很好）

 public class displayadapter4 extends ArrayAdapter<String> {
    displayadapter4()
    {
        super(instantme_check.this, R.layout.row, R.id.label, course);
    }       
    @Override
    public View getView(int position, View convertView, ViewGroup parent)
    {
        View row = super.getView(position, convertView, parent);
        TextView size1 = (TextView) row.findViewById(R.id.size);
        size1.setText("Subject: " + subject[position]);
        TextView size2 = (TextView) row.findViewById(R.id.size2);
        size2.setText("Message: " + message[position]);
        TextView size3 = (TextView) row.findViewById(R.id.size3);
        size3.setText("From: " + user[position]);

        return(row);        
    }

}

它一直给出nullpointer异常，虽然我放入arrayadapter的数据我确定没问题，因为我使用了Log.i来验证它。

至于我的错误日志

    04-07 00:33:10.714: W/dalvikvm(273): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
04-07 00:33:10.734: E/AndroidRuntime(273): FATAL EXCEPTION: main
04-07 00:33:10.734: E/AndroidRuntime(273): java.lang.NullPointerException
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:355)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.ArrayAdapter.getView(ArrayAdapter.java:323)
04-07 00:33:10.734: E/AndroidRuntime(273):  at com.Assist.assistme.instantme_check$displayadapter4.getView(instantme_check.java:172)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.AbsListView.obtainView(AbsListView.java:1315)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.ListView.makeAndAddView(ListView.java:1727)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.ListView.fillDown(ListView.java:652)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.ListView.fillFromTop(ListView.java:709)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.ListView.layoutChildren(ListView.java:1580)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.AbsListView.onLayout(AbsListView.java:1147)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.view.View.layout(View.java:7035)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1249)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1125)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.LinearLayout.onLayout(LinearLayout.java:1042)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.view.View.layout(View.java:7035)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.view.View.layout(View.java:7035)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1249)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1125)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.LinearLayout.onLayout(LinearLayout.java:1042)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.view.View.layout(View.java:7035)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.view.View.layout(View.java:7035)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.view.ViewRoot.performTraversals(ViewRoot.java:1045)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1727)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.os.Looper.loop(Looper.java:123)
04-07 00:33:10.734: E/AndroidRuntime(273):  at android.app.ActivityThread.main(ActivityThread.java:4627)
04-07 00:33:10.734: E/AndroidRuntime(273):  at java.lang.reflect.Method.invokeNative(Native Method)
04-07 00:33:10.734: E/AndroidRuntime(273):  at java.lang.reflect.Method.invoke(Method.java:521)
04-07 00:33:10.734: E/AndroidRuntime(273):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-07 00:33:10.734: E/AndroidRuntime(273):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-07 00:33:10.734: E/AndroidRuntime(273):  at dalvik.system.NativeStart.main(Native Method)
04-07 00:33:12.884: D/dalvikvm(289): GC_EXTERNAL_ALLOC freed 806 objects / 57952 bytes in 66ms

对于这篇真正冗长的帖子感到抱歉。提前谢谢。

编辑： row.xml

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

    <TextView
        android:id="@+id/label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Large Text"
        android:textSize="20sp"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <TextView
        android:id="@+id/size"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=""
        android:textSize="10sp"
        android:textAppearance="?android:attr/textAppearanceLarge" />

     <TextView
        android:id="@+id/size2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=" "
        android:textSize="10sp"
        android:textAppearance="?android:attr/textAppearanceLarge" />
       <TextView
        android:id="@+id/size3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=""
        android:textSize="10sp"
        android:textAppearance="?android:attr/textAppearanceLarge" />


</LinearLayout>

Answer 1

根据您的LogCat：

java.lang.NullPointerException
    at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:355)

问题是你传递给ArrayAdapter的超级构造函数的View id，这里：

super(instantme_check.this, R.layout.row, R.id.label, course);

您的布局中不存在，您可以通读source code来查看导致NullPointerException的确切原因和原因。

解决方案很简单：使用不同的ID或将此TextView添加到您的布局中。

使用listview setadapter获取nullpointer异常

1 个答案: