Android CursorAdapter給出java.lang.NullPointerException錯誤

Question

我在應用程序中運行自定義CursorAdapter時遇到一些問題。 根據我的logcat，我得到的錯誤是：

11-08 06:41:03.228    6109-6109/? W/System.err? java.lang.RuntimeException: Unable to start activity ComponentInfo{com.app.name/com.app.name.MyActivity}: java.lang.NullPointerException
11-08 06:41:03.229    6109-6109/? W/System.err? at com.app.name.MyActivity.onCreate(MyActivity.java:71)
11-08 06:41:03.231    6109-6109/? E/AndroidRuntime? FATAL EXCEPTION: main

發生在設置適配器的第71行（ obj.setAdapter(myAdapter) ）。 最初，我認為我的數據庫數據檢索功能（ Cursor chatCursor = mydb.selectConversation(msgId); ）沒有返回任何數據，但是在使用chatCursor.getCount（）函數對其進行測試之后，我意識到並非如此。 請協助我解決這個問題。 以下是我的活動，適配器和logcat的代碼。 提前致謝。

MyAdapter.java

public class MyAdapter extends CursorAdapter {
    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    public MyAdapter(Context context, Cursor cursor) {
        super(context, cursor, 0);
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        return LayoutInflater.from(context).inflate(R.layout.chat_left, parent, false);
    }

    @Override
    public void bindView(View view, Context context, Cursor cursor) {
        TextView user = (TextView) view.findViewById(R.id.reply_user);
        TextView msg = (TextView) view.findViewById(R.id.reply_msg);

        String theTime = cursor.getString(cursor.getColumnIndexOrThrow("message_id"));
        String theMessage = cursor.getString(cursor.getColumnIndexOrThrow("message"));

        user.setText(theTime);
        msg.setText(String.valueOf(theMessage));
    }
}

MyActivity.java

public class MyActivity extends ListActivity {
    //Utils Class
    Utils util;

    final Context context = this;
    private ProgressBar dialog;

    ListView obj;
    DBHelper mydb;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view);
        util = new Utils(this);
        mydb = new DBHelper(this);

        Bundle extras = getIntent().getExtras();
        final Integer msgId = extras.getInt("id");

        obj = (ListView) findViewById(R.id.list);

        Cursor chatCursor = mydb.selectConversation(msgId);
        MyAdapter myAdapter = new MyAdapter(this, chatCursor);
        obj.setAdapter(myAdapter);
    }
}

日志貓

11-08 06:41:03.228    6109-6109/? W/System.err? java.lang.RuntimeException: Unable to start activity ComponentInfo{com.app.name/com.app.name.MyActivity}: java.lang.NullPointerException
11-08 06:41:03.229    6109-6109/? W/System.err? at com.app.name.MyActivity.onCreate(MyActivity.java:71)
11-08 06:41:03.231    6109-6109/? E/AndroidRuntime? FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.app.name/com.app.name.MyActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2351)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403)
            at android.app.ActivityThread.access$600(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5370)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.app.name.MyActivity.onCreate(MyActivity.java:71)
            at android.app.Activity.performCreate(Activity.java:5122)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1150)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2315)
                at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403)
                at android.app.ActivityThread.access$600(ActivityThread.java:165)
                at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5370)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
11-08 06:41:03.238      559-832/? W/ActivityManager? Force finishing activity com.app.name/.MyActivity
11-08 06:41:03.742      559-574/? W/ActivityManager? Activity pause timeout for ActivityRecord{42e71938 u0 com.app.name/.MyActivity}

Answer 1

看一下您的activity_view.xml。 當您嘗試使用findViewById（R.layout.list）查找列表視圖ID時，它可能不是“列表”。