Question

这是我的AsyncTask类，我在其中返回一些文本，然后想在onPostExecute方法中使用但是我得到null值，我不知道为什么我得到null-Value

class NetworkOperation extends AsyncTask<String,int[],String>
{
    static String line;
    MainActivity mainActivity;

@Override
    protected String doInBackground(String... params) {
        Log.e("Async Method",params[0]+","+params[1]);
        try 
        {
            Log.e("ASYNC try started",params[1]+"");
            String urlParameters = params[1].toString();
            URL url = new URL(params[0].toString());
            line="some text";                   //in place of this some logic is there
            Log.e("OUTPUT OF ASYNc",line);
        } 
        catch (Exception e) 
        {
        }
        Log.e("OUTPUT OF ASYNc",line);//line has data which i want
        return line;                  //return value to use in onPostExecute() method
    }   
    @Override
    protected void onPostExecute(String result) {
        if(result==null)                         //here i am getting null value
        {
            Log.e("result is null","result is null");
        }
        else
        {
            Log.e("value of result",result);
            mainActivity.setJsonData(result);
        }
    }
}

LogCat错误在下面给出

12-31 00:47:45.999: E/AndroidRuntime(2765): FATAL EXCEPTION: AsyncTask #1
12-31 00:47:45.999: E/AndroidRuntime(2765): Process: com.tatya, PID: 2765
12-31 00:47:45.999: E/AndroidRuntime(2765): java.lang.RuntimeException: An error occured while executing doInBackground()
12-31 00:47:45.999: E/AndroidRuntime(2765):     at android.os.AsyncTask$3.done(AsyncTask.java:300)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at java.util.concurrent.FutureTask.run(FutureTask.java:242)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at java.lang.Thread.run(Thread.java:841)
12-31 00:47:45.999: E/AndroidRuntime(2765): Caused by: java.lang.NullPointerException: println needs a message
12-31 00:47:45.999: E/AndroidRuntime(2765):     at android.util.Log.println_native(Native Method)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at android.util.Log.e(Log.java:232)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at com.tatya.NetworkOperation.doInBackground(MainActivity.java:149)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at com.tatya.NetworkOperation.doInBackground(MainActivity.java:1)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at android.os.AsyncTask$2.call(AsyncTask.java:288)
12-31 00:47:45.999: E/AndroidRuntime(2765):     at java.util.concurrent.FutureTask.run(FutureTask.java:237)

Answer 1

试试这种方式

  if(TextUtils.isEmpty(result))

而不是

  if(result==null)

我在onPostExecute（字符串结果）上获得空值？

1 个答案: