Android 在调用web服务期间关闭应用程序

我正在编写一个应用程序，它必须从web服务获取一些json对象。 它运转得很好。但是，我想找到一种方法避免用户在无法下载这些json对象的情况下使用。 所以，我使用了一个错误的URL。 现在，我的应用程序强制关闭而不避开用户

电话：

/*
 * Async call to fill the category spinner
 */
private class CallCategory extends AsyncTask<Void,Void,Void>{
private ProgressDialog dialog;

protected void onPreExecute() {
    this.dialog = ProgressDialog.show(ApPictureActivity.this, "Chargement", "Récupération des catégories...", true);
}
    protected void onPostExecute(Void v) {
        dialog.cancel();
        Log.i("fill the spiner", _ListCategory.toString());
        if(!_ListCategory.isEmpty())
            FillSpinner();
        else
        {
            AlertDialog alertDialog = new AlertDialog.Builder(ApPictureActivity.this).create();
            alertDialog.setTitle(getResources().getString(R.string.errorCategoryTitle));
            alertDialog.setMessage(getResources().getString(R.string.errorCategoryMessage));
            //add "Ok button"
             alertDialog.setButton("OK", new DialogInterface.OnClickListener() {  
                  public void onClick(DialogInterface dialog, int which) {  
                    return;  
                } }); 
            alertDialog.show();
            //log
            Log.i("List category empty", "No categories");
            //ApPictureActivity.this.finish();
        }
    }

    protected Void doInBackground(Void... params) {
        try{
        _ListCategory = ServerCall.GetCategory();}
        catch (Exception e) {
            Log.i("load categories error",e.toString());
        }
        return null;
    }
}

我确信这段代码使用的是正确的URL。所以这不是一个实现问题。可能是一个例外没有被抓住

---

尊敬。

我跟随了dj aquell adivies，并通过以下方式更改了onPostExecute方法：

    protected void onPostExecute(Void v) {
        dialog.cancel();
        if(_ListCategory != null){
            Log.i("fill the spiner", _ListCategory.toString());
            FillSpinner();}
        else
        {
            AlertDialog alertDialog = new AlertDialog.Builder(ApPictureActivity.this).create();
            alertDialog.setTitle(getResources().getString(R.string.errorCategoryTitle));
            alertDialog.setMessage(getResources().getString(R.string.errorCategoryMessage));
            //add "Ok button"
             alertDialog.setButton("OK", new DialogInterface.OnClickListener() {  
                  public void onClick(DialogInterface dialog, int which) {  
                        //log
                        Log.i("List category empty", "No categories");
                        ApPictureActivity.this.finish();
                } }); 
            alertDialog.show();
        }
    }

---

异常的Logcat输出@David ApPictureActivity.java文件中的第299行是哪一行？@djaqeel Log.i（“填充spiner”，_ListCategory.toString（））@djaqeel位于AppictureActivity顶部（CallCategory是AppictureActivity文件中的一个实习生类）。我也试着抑制这一行，但这并没有改变问题方法返回null！！！由于任何原因。

07-09 09:37:49.446: E/AndroidRuntime(4322): Uncaught handler: thread main exiting due to uncaught exception
07-09 09:37:49.455: E/AndroidRuntime(4322): java.lang.NullPointerException
07-09 09:37:49.455: E/AndroidRuntime(4322):     at ApPicture.Android.ApPictureActivity$CallCategory.onPostExecute(ApPictureActivity.java:299)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at ApPicture.Android.ApPictureActivity$CallCategory.onPostExecute(ApPictureActivity.java:1)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at android.os.AsyncTask.finish(AsyncTask.java:417)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at android.os.AsyncTask.access$300(AsyncTask.java:127)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at android.os.Looper.loop(Looper.java:123)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at android.app.ActivityThread.main(ActivityThread.java:4363)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at java.lang.reflect.Method.invokeNative(Native Method)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at java.lang.reflect.Method.invoke(Method.java:521)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
07-09 09:37:49.455: E/AndroidRuntime(4322):     at dalvik.system.NativeStart.main(Native Method)

    protected void onPostExecute(Void v) {
        dialog.cancel();
        if(_ListCategory != null){
            Log.i("fill the spiner", _ListCategory.toString());
            FillSpinner();}
        else
        {
            AlertDialog alertDialog = new AlertDialog.Builder(ApPictureActivity.this).create();
            alertDialog.setTitle(getResources().getString(R.string.errorCategoryTitle));
            alertDialog.setMessage(getResources().getString(R.string.errorCategoryMessage));
            //add "Ok button"
             alertDialog.setButton("OK", new DialogInterface.OnClickListener() {  
                  public void onClick(DialogInterface dialog, int which) {  
                        //log
                        Log.i("List category empty", "No categories");
                        ApPictureActivity.this.finish();
                } }); 
            alertDialog.show();
        }
    }