自定义listview的ArrayAdapter报空指针

============问题描述============

布局activity_list_view_test.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin"

    android:orientation="vertical"

    tools:context=".ListViewTest" >



    <TextView

        android:id="@+id/txtselection"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content" >

    </TextView>



    <ListView

        android:id="@android:id/list"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:drawSelectorOnTop="false"

        android:orientation="vertical" >

    </ListView>



</LinearLayout>

row  list_vew_test_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="horizontal" >



    <ImageView

        android:id="@+id/icon"

        android:layout_width="22dp"

        android:layout_height="wrap_content"

        android:paddingLeft="2dp"

        android:paddingRight="2dp"

        android:paddingTop="2dp"

        android:src="@drawable/ok" />



    <TextView

        android:id="@+id/label"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:textSize="44sp" />



</LinearLayout>

java代码

public class ListViewTest extends ListActivity {



    TextView selection;

    String[] items = {

            "Apple", "orange", "Banana", "peach", "Grape", "Strawberry", "matermelon", "lemon"

    };



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_list_view_test);

        //setContentView(R.layout.list_vew_test_row);

        // setListAdapter(new ArrayAdapter<String>(this,

        // android.R.layout.simple_list_item_1, items));

        setListAdapter(new IconicAdapter());



        selection = (TextView)findViewById(R.id.txtselection);

        selection.setText("Please select");

    }



    @Override

    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.

        getMenuInflater().inflate(R.menu.list_view_test, menu);

        return true;

    }



    public void onListItemClick(ListView parent, View v, int position, long id) {



        selection.setText(items[position]);

    }



    class IconicAdapter extends ArrayAdapter {

        IconicAdapter() {

            super(ListViewTest.this, R.layout.list_vew_test_row, items);

        }



        public View getView(int position, View convertView, ViewGroup parent) {



            LayoutInflater inflater = getLayoutInflater();

            View row = inflater.inflate(R.layout.list_vew_test_row, parent, false);

            TextView label = (TextView)findViewById(R.id.label);

            label.setText(items[position]);



            ImageView icon = (ImageView)findViewById(R.id.icon);

            if (items[position].length() >= 5) {

                icon.setImageResource(R.drawable.ok);

            } else {

                icon.setImageResource(R.drawable.delete);

            }

            return row;

        }

    }

}

error：

D/TextLayoutCache( 8977): Using debug level: 0 - Debug Enabled: 0

D/AndroidRuntime( 8977): Shutting down VM

W/dalvikvm( 8977): threadid=1: thread exiting with uncaught exception (group=0x40aaf210)

E/AndroidRuntime( 8977): FATAL EXCEPTION: main

E/AndroidRuntime( 8977): java.lang.NullPointerException

E/AndroidRuntime( 8977): 	at com.example.test.ListViewTest$IconicAdapter.getView(ListViewTest.java:58)

E/AndroidRuntime( 8977): 	at android.widget.AbsListView.obtainView(AbsListView.java:2043)

E/AndroidRuntime( 8977): 	at android.widget.ListView.measureHeightOfChildren(ListView.java:1244)

E/AndroidRuntime( 8977): 	at android.widget.ListView.onMeasure(ListView.java:1155)

E/AndroidRuntime( 8977): 	at android.view.View.measure(View.java:12897)

E/AndroidRuntime( 8977): 	at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4805)

E/AndroidRuntime( 8977): 	at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1385)

E/AndroidRuntime( 8977): 	at android.widget.LinearLayout.measureVertical(LinearLayout.java:676)

E/AndroidRuntime( 8977): 	at android.widget.LinearLayout.onMeasure(LinearLayout.java:557)

E/AndroidRuntime( 8977): 	at android.view.View.measure(View.java:12897)

E/AndroidRuntime( 8977): 	at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4805)

E/AndroidRuntime( 8977): 	at android.widget.FrameLayout.onMeasure(FrameLayout.java:297)

E/AndroidRuntime( 8977): 	at android.view.View.measure(View.java:12897)

E/AndroidRuntime( 8977): 	at android.widget.LinearLayout.measureVertical(LinearLayout.java:828)

E/AndroidRuntime( 8977): 	at android.widget.LinearLayout.onMeasure(LinearLayout.java:557)

E/AndroidRuntime( 8977): 	at android.view.View.measure(View.java:12897)

E/AndroidRuntime( 8977): 	at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4805)

E/AndroidRuntime( 8977): 	at android.widget.FrameLayout.onMeasure(FrameLayout.java:297)

E/AndroidRuntime( 8977): 	at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2092)

E/AndroidRuntime( 8977): 	at android.view.View.measure(View.java:12897)

E/AndroidRuntime( 8977): 	at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1064)

E/AndroidRuntime( 8977): 	at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2442)

E/AndroidRuntime( 8977): 	at android.os.Handler.dispatchMessage(Handler.java:99)

E/AndroidRuntime( 8977): 	at android.os.Looper.loop(Looper.java:137)

E/AndroidRuntime( 8977): 	at android.app.ActivityThread.main(ActivityThread.java:4441)

E/AndroidRuntime( 8977): 	at java.lang.reflect.Method.invokeNative(Native Method)

E/AndroidRuntime( 8977): 	at java.lang.reflect.Method.invoke(Method.java:511)

E/AndroidRuntime( 8977): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)

E/AndroidRuntime( 8977): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)

E/AndroidRuntime( 8977): 	at dalvik.system.NativeStart.main(Native Method)

W/ActivityManager(  376):   Force finishing activity com.example.test/.ListViewTest

58行：

label.setText(items[position]);

============解决方案1============

TextView label = (TextView)findViewById(R.id.label);把这句话改成TextView label = (TextView)row.findViewById(R.id.label);
因为这里要指定哪个页面的id。

============解决方案2============

TextView label = (TextView) row.findViewById(R.id.label);



ImageView icon = (ImageView) row.findViewById(R.id.icon);