我已经使用listview完成了一个程序..我得到了一个运行时异常。请帮助我。 这是我的logcat
09-08 09:02:46.924: D/AndroidRuntime(2319): Shutting down VM
09-08 09:02:46.924: D/AndroidRuntime(2319): --------- beginning of crash
09-08 09:02:46.949: E/AndroidRuntime(2319): FATAL EXCEPTION: main
09-08 09:02:46.949: E/AndroidRuntime(2319): Process: com.example.todo, PID: 2319
09-08 09:02:46.949: E/AndroidRuntime(2319): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.todo/com.example.todo.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.app.ActivityThread.access$800(ActivityThread.java:144)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.os.Handler.dispatchMessage(Handler.java:102)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.os.Looper.loop(Looper.java:135)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.app.ActivityThread.main(ActivityThread.java:5221)
09-08 09:02:46.949: E/AndroidRuntime(2319): at java.lang.reflect.Method.invoke(Native Method)
09-08 09:02:46.949: E/AndroidRuntime(2319): at java.lang.reflect.Method.invoke(Method.java:372)
09-08 09:02:46.949: E/AndroidRuntime(2319): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
09-08 09:02:46.949: E/AndroidRuntime(2319): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
09-08 09:02:46.949: E/AndroidRuntime(2319): Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.widget.ListView.setAdapter(ListView.java:487)
09-08 09:02:46.949: E/AndroidRuntime(2319): at com.example.todo.MainActivity.onCreate(MainActivity.java:32)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.app.Activity.performCreate(Activity.java:5937)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
09-08 09:02:46.949: E/AndroidRuntime(2319): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
09-08 09:02:46.949: E/AndroidRuntime(2319): ... 10 more
09-08 09:02:51.130: I/Process(2319): Sending signal. PID: 2319 SIG: 9
09-08 09:03:06.387: I/art(2342): Background sticky concurrent mark sweep GC freed 1740(104KB) AllocSpace objects, 0(0B) LOS objects, 18% free, 508KB/623KB, paused 1.661ms total 107.680ms
09-08 09:03:06.602: I/art(2342): Background partial concurrent mark sweep GC freed 903(101KB) AllocSpace objects, 0(0B) LOS objects, 42% free, 699KB/1211KB, paused 3.624ms total 204.798ms
09-08 09:03:06.607: D/AndroidRuntime(2342): Shutting down VM
09-08 09:03:06.608: E/AndroidRuntime(2342): FATAL EXCEPTION: main
09-08 09:03:06.608: E/AndroidRuntime(2342): Process: com.example.todo, PID: 2342
09-08 09:03:06.608: E/AndroidRuntime(2342): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.todo/com.example.todo.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.app.ActivityThread.access$800(ActivityThread.java:144)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.os.Handler.dispatchMessage(Handler.java:102)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.os.Looper.loop(Looper.java:135)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.app.ActivityThread.main(ActivityThread.java:5221)
09-08 09:03:06.608: E/AndroidRuntime(2342): at java.lang.reflect.Method.invoke(Native Method)
09-08 09:03:06.608: E/AndroidRuntime(2342): at java.lang.reflect.Method.invoke(Method.java:372)
09-08 09:03:06.608: E/AndroidRuntime(2342): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
09-08 09:03:06.608: E/AndroidRuntime(2342): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
09-08 09:03:06.608: E/AndroidRuntime(2342): Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.widget.ListView.setAdapter(ListView.java:487)
09-08 09:03:06.608: E/AndroidRuntime(2342): at com.example.todo.MainActivity.onCreate(MainActivity.java:32)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.app.Activity.performCreate(Activity.java:5937)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
09-08 09:03:06.608: E/AndroidRuntime(2342): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
09-08 09:03:06.608: E/AndroidRuntime(2342): ... 10 more
这是我的代码...... 公共类MainActivity扩展ActionBarActivity {
private ArrayList<String> arrayList;
private ArrayAdapter<String> adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView listView=(ListView)findViewById(R.id.l1);
final EditText et=(EditText)findViewById(R.id.et1);
Button btn=(Button)findViewById(R.id.b1);
adapter=new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1,arrayList);
listView.setAdapter(adapter);
btn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
String newitem=et.getText().toString();
arrayList.add(newitem);
adapter.notifyDataSetChanged();
et.setText("");
}
});
}
这是xml版本
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ff000f"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.todo.MainActivity" >
<Button
android:id="@+id/b1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:text="add" />
<ListView
android:id="@+id/l1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@+id/b1"
android:layout_alignRight="@+id/b1" >
</ListView>
<EditText
android:id="@+id/et1"
android:background="#ffffff"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/b1"
android:layout_alignBottom="@+id/b1"
android:layout_alignLeft="@+id/l1"
android:ems="10" />
</RelativeLayout>
答案 0 :(得分：0)
你应该初始化你的arrayList。
ArrayList<String> arrayList = null;
您正在传递给适配器null