java - 突然出现空指针异常

Question

早些时候，我的相同代码工作正常，但突然我得到NULL指针异常，Logcat说行号:251，见下文:

   ProgressBar progress = (ProgressBar)v.findViewById(R.id.progressBar);

现在我想知道为什么我会得到 NPE，而我的相同代码在几个小时前运行良好？

每当我在 getView(...) 中使用 startUpload(position) 方法时遇到这个问题，否则不会得到，但在过去我使用 >startUpload(position) 在相同的位置，但没有得到异常，那么为什么现在呢？

Logcat:

11-21 05:45:43.822: W/dalvikvm(1559): threadid=1: thread exiting with uncaught exception (group=0x41465700)
11-21 05:45:43.872: E/AndroidRuntime(1559): FATAL EXCEPTION: main
11-21 05:45:43.872: E/AndroidRuntime(1559): java.lang.NullPointerException
11-21 05:45:43.872: E/AndroidRuntime(1559):     at com.example.demo.UploadActivity$2$1.run(UploadActivity.java:251)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at android.os.Handler.handleCallback(Handler.java:730)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at android.os.Handler.dispatchMessage(Handler.java:92)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at android.os.Looper.loop(Looper.java:137)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at android.app.ActivityThread.main(ActivityThread.java:5103)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at java.lang.reflect.Method.invokeNative(Native Method)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at java.lang.reflect.Method.invoke(Method.java:525)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-21 05:45:43.872: E/AndroidRuntime(1559):     at dalvik.system.NativeStart.main(Native Method)

代码:-

public View getView(final int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub

        LayoutInflater inflater = (LayoutInflater) context
        .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        if (convertView == null) {
        convertView = inflater.inflate(R.layout.activity_column, null);
        }

        startUpload(position);
    //  statusWhenFinish(position, resServer);

            return convertView;

    }
    } 


   //Upload
    public void startUpload(final int position) {      

    Runnable runnable = new Runnable() {

    public void run() {

     handler.post(new Runnable() {
    public void run() {

    View v = lstView.getChildAt(position - lstView.getFirstVisiblePosition());

    // Show ProgressBar
    ProgressBar progress = (ProgressBar)v.findViewById(R.id.progressBar);
    progress.setVisibility(View.VISIBLE);

    // Status
    TextView status = (TextView)v.findViewById(R.id.ColStatus);
    status.setText("Uploading..");

    new UploadFileAsync().execute(String.valueOf(position));   
    }
    });

    }
    };
    new Thread(runnable).start();
    }


           // When UPload Finish
    protected void statusWhenFinish(int position, String resServer) {

    View v = lstView.getChildAt(position - lstView.getFirstVisiblePosition());

    // Show ProgressBar
    ProgressBar progress = (ProgressBar)v.findViewById(R.id.progressBar);
    progress.setVisibility(View.GONE);


    // Status
    TextView status = (TextView)v.findViewById(R.id.ColStatus);

    /*** Default Value ***/
    String strStatusID = "0";
    String strError = "";

    try {      

    JSONObject c = new JSONObject(resServer);
    strStatusID = c.getString("StatusID");
    strError = c.getString("Error");
    } catch (JSONException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }

    // Prepare Status
    if(strStatusID.equals("0"))
    {
    // When update Failed
    status.setText("Already exist" + strError);
    status.setTextColor(Color.RED);

    // Enabled Button again
    Button btnUpload = (Button) v.findViewById(R.id.btnUpload);
    btnUpload.setText("Uploaded");
    btnUpload.setTextColor(Color.RED);
    btnUpload.setEnabled(true);
    }
    else
    {
    status.setText("Upload Completed.");
    status.setTextColor(Color.GREEN);
    }

    }

Answer 1

这种错误有时可以通过清理项目来修复。