Android AsyncTask使用心得及錯誤處理-只能在主線程改變UI組件

標籤：android asynctask   異常   網路   線程   

    大家肯定都會經常使用AsyncTask這個類，特別是在網路處理中，先看改正後的代碼：這是正常的代碼：

class sendKeyTask extends AsyncTask<String, Void, Integer>{@Overrideprotected void onPostExecute(Integer resultCode) {// TODO Auto-generated method stubsuper.onPostExecute(resultCode);switch (resultCode) {case 6000:NotifyHelper.popNotifyInfo(InnerQuestionActivity.this, "使用者資訊異常", "");break;case 6001:NotifyHelper.popNotifyInfo(InnerQuestionActivity.this, "其他異常", "");break;case 6002:break;default:break;}// 隱藏IMEInputMethodManager imm = (InputMethodManager) getApplicationContext().getSystemService(Context.INPUT_METHOD_SERVICE);// 顯示或者隱藏IMEimm.toggleSoftInput(0, InputMethodManager.HIDE_NOT_ALWAYS);innerQuestionEdit.setText("");//從新重新整理new getQuestionDetailTack().execute(1);}@Overrideprotected Integer doInBackground(String... data) {// TODO Auto-generated method stubint resultCode=4001;HttpClient client= new DefaultHttpClient();HttpPost post = new HttpPost("http://diandianapp.sinaapp.com/add_key.php");StringBuilder builder = new StringBuilder(); List<NameValuePair> paramsList=new ArrayList<NameValuePair>();paramsList.add(new BasicNameValuePair("access_token", data[0]));paramsList.add(new BasicNameValuePair("user_name", data[1]));paramsList.add(new BasicNameValuePair("key_detail", data[2]));paramsList.add(new BasicNameValuePair("question_id", data[3]));for(int i=0;i<jpegDataList.size();i++){paramsList.add(new BasicNameValuePair("img"+String.valueOf(i), jpegDataList.get(i)));}try {post.setEntity( new UrlEncodedFormEntity(paramsList,HTTP.UTF_8));} catch (UnsupportedEncodingException e1) {e1.printStackTrace();}try { HttpResponse response = client.execute(post); HttpEntity entity = response.getEntity();BufferedReader reader = new BufferedReader(new InputStreamReader(entity.getContent())); for (String s = reader.readLine(); s != null; s = reader.readLine()) { builder.append(s); } JSONObject jsonObject = new JSONObject(builder.toString());String stateCodeStr = jsonObject.getString("state_code"); resultCode=Integer.parseInt(stateCodeStr);} catch (ClientProtocolException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (JSONException e) {// TODO Auto-generated catch blocke.printStackTrace();//處理請求失敗}finally{}return resultCode;}}

可能有人會說，我讓doInBackground返回一個參數，再在onPostExecute裡面處理不是多次一舉嗎？但是，當你真的將兩部分合成後，會發現，竟然報錯了！報錯內容大體為UI內容只能在主線程更改；這是為什麼呢！

NotifyHelper.popNotifyInfo(InnerQuestionActivity.this, "其他異常", "");是對對話提示框的一個彈出方法封裝，這是對UI介面的操作，問題應該就出在這兒了！

我們翻開google的說明看下：

protected abstract Result doInBackground (Params... params)Added in API level 3

Override this method to perform a computation on a background thread. The specified parameters are the parameters passed toexecute(Params...) by the caller of this task. This method can callpublishProgress(Progress...) to publish updates on the UI thread.

Parameters

params	The parameters of the task.

Returns

• A result, defined by the subclass of this task.

protected void onPostExecute(Result result) Added in API level 3

Runs on the UI thread after doInBackground(Params...). The specified result is the value returned bydoInBackground(Params...).

This method won‘t be invoked if the task was cancelled.

Parameters

result	The result of the operation computed by doInBackground(Params...).

See Alsoprotected void onPreExecute() Added in API level 3

Runs on the UI thread before doInBackground(Params...).

我們可以看出，這幾個重載方法只有doInBackground是在後台線程啟動並執行，而後台是不能執行更新線程的操作的！

我們必須要在doInbackground中，返回耗時操作的處理結果，再從onPostExecute中根據doInBackground返回的參數進行UI組件的操作！

doInBackground

Android AsyncTask使用心得及錯誤處理-只能在主線程改變UI組件