Question

有很多与我的问题相关的问题，但它们都没有解决我的问题。我几乎尝试了所有这些。

我在从网络源获取数据后尝试更改布局中的值，但我每次都会获得nullpointerexception。

错误我正在

03-25 18:05:43.071: E/AndroidRuntime(4832): FATAL EXCEPTION: main
    03-25 18:05:43.071: E/AndroidRuntime(4832): java.lang.NullPointerException
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at com.wishberg.app.CommunityPageActivity$SendRequest.onPostExecute(CommunityPageActivity.java:158)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at com.wishberg.app.CommunityPageActivity$SendRequest.onPostExecute(CommunityPageActivity.java:1)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at android.os.AsyncTask.finish(AsyncTask.java:631)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at android.os.Handler.dispatchMessage(Handler.java:99)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at android.os.Looper.loop(Looper.java:137)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at android.app.ActivityThread.main(ActivityThread.java:5103)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at java.lang.reflect.Method.invokeNative(Native Method)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at java.lang.reflect.Method.invoke(Method.java:525)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    03-25 18:05:43.071: E/AndroidRuntime(4832):     at dalvik.system.NativeStart.main(Native Method)

这是我的活动类

public class CommunityPageActivity extends Activity {

    public String wishid = null;
    private Context context = null;
    public String TAG = "communitypage";

    private String cachedName = "community";
    private static final int URL_LOADER = 0;
    private Menu optionsMenu;
    private ProgressDialog progress;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);

        Intent i = getIntent();
        wishid = i.getStringExtra("id");
        context = getApplicationContext();

        ActionBar actionBar = getActionBar();
        actionBar.setDisplayShowTitleEnabled(false);

        Common.setRefreshActionButtonState(true, optionsMenu);

            progress = new ProgressDialog(this);
    progress.setMessage("Loading...");
    progress.setIndeterminate(true);
    progress.show();

        setContentView(R.layout.community);
    }


    private class SendRequest extends AsyncTask<String, Integer, String> {

        // http://www.mysamplecode.com/2012/11/android-progress-bar-example.html

        ViewHolder holder = null;
        protected String doInBackground(String... requestURL) {

            String data = "";
            HttpURLConnection httpUrlConnection = null;

            try {

                data = Common.readStream(in);

            } catch (MalformedURLException exception) {
                Log.e(TAG, "MalformedURLException");
            } catch (IOException exception) {
                Log.e(TAG, "IOException");
            } finally {
                if (null != httpUrlConnection)
                    httpUrlConnection.disconnect();
            }
            return data;

        }

        protected void onPostExecute(String jsonString) {

            progress.dismiss();
            System.out.println(jsonString);
            JSONArray jsonArray = Common.getArrayFromJsonString(jsonString, 0);


            Inflater inflater;
//          View v = inflater.inflate(R.layout.community);
            holder.txtWishName = (TextView) CommunityPageActivity.this.findViewById(R.id.tv_communitywishname);
            System.out.println(holder);
            System.out.println(jsonArray);
        }


        /* private view holder class */
        private class ViewHolder {
            ImageView imageView;
            TextView txtWishName;
            ImageButton btn_touchwood;
            ImageButton btn_addwish;
            TextView tvGesture;
            TextView tvNotes;
        }

    }

}

Answer 1

删除此行

 progress.dismiss();

你还没有初始化，也没有在任何地方使用.. 根据评论

你的

ViewHolder holder is null

Answer 2

首先，不要在AsyncTask内初始化您的小部件。不要在那里使用inflater。您应该初始化onCreate(..)中的所有内容。

然后，您可以在AsyncTask中执行昂贵的操作（HTTP连接等）。然后在onPostExecute中，您应该更新您的Activity / Fragment中的已初始化的UI小部件。至少这就是AsyncTask的意思。

正如已经提到的那样，您的holder变量未初始化，这就是您首先获得异常的原因。

更新：此外，在onPostExecute()中解析您的JSON数据是一个坏主意，因为它可能会否定您对使用AsyncTask所期望的效果 - 此方法在UI上运行 - 并且可以冻结它。将内容移至doInBackground()。

将数据从asynctask传递到活动视图

2 个答案: