在我的 MainActivity 类中,我有一个listview_fuellen
填充我的列表视图的方法。
public void listview_fuellen(){
DBHelper db = new DBHelper(this);
ListView lv = (ListView) findViewById(R.id.lvKinder);
Cursor c = db.select();
int count = c.getCount();
String values[] = new String[count+1];
List<String> auswahl = new ArrayList<String>();
int i = 0;
System.out.println("$$$$$$$$$$$$$$$$$$$$$$$1" + c.getCount());
while(c.moveToNext())
{
values[i]= c.getString(c.getColumnIndex("name"));
auswahl.add(c.getString(c.getColumnIndex("name")));
System.out.println("SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS" + auswahl.get(i).toString());
i++;
}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.list_black_text,R.id.list_content, auswahl);
lv.setAdapter(adapter);
}
现在,在我将数据添加到列表视图显示的数据库的另一个类中,我尝试调用此方法。
db.insert(name, zeit, geschlecht);
MainActivity ma = new MainActivity();
ma.listview_fuellen();
MainActivity 的构造函数是默认构造函数:
public void MainActivity(){
}
现在,当我执行我的应用程序时,我的方法得到一个 NullpointerException listview_fuellen()
:
05-07 14:08:17.609: E/AndroidRuntime(25654): FATAL EXCEPTION: main
05-07 14:08:17.609: E/AndroidRuntime(25654): java.lang.NullPointerException
05-07 14:08:17.609: E/AndroidRuntime(25654): at android.app.Activity.findViewById(Activity.java:1839)
05-07 14:08:17.609: E/AndroidRuntime(25654): at com.example.unserekinder.MainActivity.listview_fuellen(MainActivity.java:129)
05-07 14:08:17.609: E/AndroidRuntime(25654): at com.example.unserekinder.NeuesKind$1.onClick(NeuesKind.java:57)
05-07 14:08:17.609: E/AndroidRuntime(25654): at android.view.View.performClick(View.java:4204)
05-07 14:08:17.609: E/AndroidRuntime(25654): at android.view.View$PerformClick.run(View.java:17355)
05-07 14:08:17.609: E/AndroidRuntime(25654): at android.os.Handler.handleCallback(Handler.java:725)
05-07 14:08:17.609: E/AndroidRuntime(25654): at android.os.Handler.dispatchMessage(Handler.java:92)
05-07 14:08:17.609: E/AndroidRuntime(25654): at android.os.Looper.loop(Looper.java:137)
05-07 14:08:17.609: E/AndroidRuntime(25654): at android.app.ActivityThread.main(ActivityThread.java:5041)
05-07 14:08:17.609: E/AndroidRuntime(25654): at java.lang.reflect.Method.invokeNative(Native Method)
05-07 14:08:17.609: E/AndroidRuntime(25654): at java.lang.reflect.Method.invoke(Method.java:511)
05-07 14:08:17.609: E/AndroidRuntime(25654): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-07 14:08:17.609: E/AndroidRuntime(25654): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-07 14:08:17.609: E/AndroidRuntime(25654): at dalvik.system.NativeStart.main(Native Method)
有人能告诉我为什么吗?