android - Android 处理程序 NullPointerException

Question

Activity创建一个新的Thread.
该方法通过输入流run()获取一个对象 ( )。vector
现在我想Vector在ListView被调用的direc.
就是这样......但它不起作用并抛出一个Exception.

编码：

public class FileExplorerActivity extends Activity implements Runnable
{
    public static final String TAG="ricky";
    Vector<String> dirs = new Vector<String>();
    ListView direc;
    static ArrayAdapter<String> arrayAdapter;
    Handler handler;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fileexplorer);
        direc = (ListView) findViewById(R.id.directoriesss);
        handler = new Handler();
        Thread thread = new Thread(this);
        thread.start();
    }

    public FileExplorerActivity() 
    {

    }

    public void run()
    {
        Log.d(TAG, "FileExplorer: Thread started");
        try
        {
            Log.d(TAG, "FileExplorer: reading data");
            dirs = (Vector<String>) ConnectionThread.din.readObject();
            Log.d(TAG, "FileExplorer: read data");
            arrayAdapter = new ArrayAdapter<String>(this, 
                                     android.R.layout.activity_list_item,
                                     android.R.id.text2 , dirs);            
            Log.d(TAG, "FileExplorer: ArrayAdapter created");

            handler.post( new Runnable() {
                public void run()
                {
                    Log.d(TAG, "FileExplorer: In handler Thread");
                    direc.setAdapter(arrayAdapter);
                    Log.d(TAG, "FileExplorer: Updated UI");
                }
            });

            Log.d(TAG, "FileExplorer: Directory set");
        }catch (Exception e) {
            Log.d(TAG, "FileExplorerActivity: Exception:"+e.getMessage());
        }
    }
}

这是 Logcat 不得不说的：

> 1. 05-24 20:14:46.601  7759  7834 D ricky   : FileExplorer: Thread started
> 2. 05-24 20:14:46.601  7759  7834 D ricky   : FileExplorer: reading data
> 3. 05-24 20:14:46.648  7759  7834 D ricky   : FileExplorer: read data
> 4. 05-24 20:14:46.648  7759  7834 D ricky   : FileExplorer: ArrayAdapter created
> 5. 05-24 20:14:46.648  7759  7834 D ricky   : FileExplorer: Directory set
> 6. 05-24 20:14:46.656  7759  7759 D ricky   : FileExplorer: In handler Thread
> 7. 05-24 20:14:46.656  7759  7759 D ricky   : FileExplorer: Updated UI
> 8. 05-24 20:14:46.664  7759  7759 D AndroidRuntime: Shutting down VM
> 9. 05-24 20:14:46.664  7759  7759 W dalvikvm: threadid=1: thread exiting with uncaught 10. exception (group=0x4001e560)
> 11. 05-24 20:14:46.687  7759  7759 E AndroidRuntime: FATAL EXCEPTION: main
> 12. 05-24 20:14:46.687  7759  7759 E AndroidRuntime: java.lang.NullPointerException
> 13. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:353)
> 14. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.ArrayAdapter.getView(ArrayAdapter.java:323)
> 15. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.AbsListView.obtainView(AbsListView.java:1456)
> 16. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.ListView.measureHeightOfChildren(ListView.java :1291)
> 17. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.ListView.onMeasure(ListView.java:1202)
> 18. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.View.measure(View.java:8355)
> 19. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java :3279)
> 20. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
> 21. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.LinearLayout.measureHorizontal(LinearLayout.ja va:701)
> 22. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.LinearLayout.onMeasure(LinearLayout.java:311)
> 23. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.View.measure(View.java:8355)
> 24. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java :3279)
> 25. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
> 26. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.View.measure(View.java:8355)
> 27. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.LinearLayout.measureVertical(LinearLayout.java :531)
> 28. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
> 29. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.View.measure(View.java:8355)
> 30. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java :3279)
> 31. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
> 32. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.View.measure(View.java:8355)
> 33. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.ViewRoot.performTraversals(ViewRoot.java:882)
> 34. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.view.ViewRoot.handleMessage(ViewRoot.java:1917)
> 35. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.os.Handler.dispatchMessage(Handler.java:99)
> 36. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.os.Looper.loop(Looper.java:130)
> 37. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at android.app.ActivityThread.main(ActivityThread.java:3859)
> 38. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at java.lang.reflect.Method.invokeNative(Native Method)
> 39. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at java.lang.reflect.Method.invoke(Method.java:507)
> 40. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
> 41. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
> 42. 05-24 20:14:46.687  7759  7759 E AndroidRuntime:        at dalvik.system.NativeStart.main(Native Method)

score 1 · Accepted Answer

请注意NullPointerException发生的行：

android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:353)

这是因为android.R.layout.activity_list_item不包含android.R.id.text2.

您可以android.R.id.text1改用或将行布局替换为simple_list_item_2.

我建议首先创建自己的行布局来避免这些情况。

score 0 · Accepted Answer

移动这个

arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.activity_list_item,
        android.R.id.text2 , dirs);

在你的 run() 方法中，以便它在 UI 线程上运行。您不应该在 UI 线程之外创建 ArrayAdapter。

android - Android 处理程序 NullPointerException

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