在 AsyncTask doInBackground 中执行函数时出错

Question

我正在尝试从 URL 加载一些图像。

我有一个私人空间来完成所有的工作。它有效...但我有一个问题，我想在加载图像时显示对话框进度...

我正在尝试使用 AsyncTask，但在执行 doInBackground 时遇到问题！

这是我的代码：

    @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    new EjecutarTarea().execute();



}


    private  void Principal() {
    //Code to download images from URL
    }


    public class EjecutarTarea extends AsyncTask<Void, Void, Void> {

    protected void onPreExecute() {
        dialog = new ProgressDialog(StadioNenaActivity.this);
        dialog.setMessage("Cargando..");
        dialog.setIndeterminate(true);
        dialog.setCancelable(false);
        dialog.show();
    }


    protected Void doInBackground(Void... Unsed) {

      Principal();  //i have an error here 
      return null;
    }

    protected void onProgressUpdate(Void... unused) {

    }

    protected void onPostExecute(Void unused) {
        dialog.dismiss();
    }
  }

感谢您的帮助！

---

这是 de log 上的错误...它在我的代码 PRINCIPAL() 的某些部分返回 null ....

我不知道为什么，当我将 PRINCIPAL 放入 Oncreate 中时，它工作得很好！

   10-10 17:56:01.988: ERROR/AndroidRuntime(10907): FATAL EXCEPTION: AsyncTask #1
    10-10 17:56:01.988: ERROR/AndroidRuntime(10907): java.lang.RuntimeException: An      error    occured while executing doInBackground()
    10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at android.os.AsyncTask$3.done  (AsyncTask.java:200)
    10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
   10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
   10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
   10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
   10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
   10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
   10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at java.lang.Thread.run(Thread.java:1096)
   10-10 17:56:01.988: ERROR/AndroidRuntime(10907): Caused by: java.lang.NullPointerException
   10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:112)
  10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at org.json.JSONTokener.nextValue(JSONTokener.java:90)
  10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at org.json.JSONArray.<init>(JSONArray.java:87)
  10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at org.json.JSONArray.<init>(JSONArray.java:103)
  10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at Stadio.bacha.stadionena.StadioNenaActivity.Principal(StadioNenaActivity.java:121)
  10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at Stadio.bacha.stadionena.StadioNenaActivity$EjecutarTarea.doInBackground(StadioNenaActivity.java:262)
10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at Stadio.bacha.stadionena.StadioNenaActivity$EjecutarTarea.doInBackground(StadioNenaActivity.java:1)
10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
10-10 17:56:01.988: ERROR/AndroidRuntime(10907):     ... 4 more

当我这样做时：

    @Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Principal();

}

它可以工作，但它不显示对话框进度......

Answer 1

问题是调用doInBackground()时出现NullPointerException。确保在调用 AsyncTask.execute() 之前所有数据可用或提供某种阻塞机制。

Answer 2

确保您的网址正确。
我收到此错误是因为我使用了 192.168.1.173/webroot 路径...
我的意思是没有我们的 http:// 部分作为 url。
我尝试使用后

http://192.168.1.173/web application path ...

效果很好。