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在android4.0以下设备上onPostExecute不执行，doInBackground也无抛出异常。
在android4.2以上设备上onPostExecute是执行的，没问题。
那么问题就来了，一路查寻，牵扯出好多问题。
以下是我个人遇到的情况，新建个测试AsyncTask项目没有问题，但是在原项目下问题就来了。
AndroidManifest.xml里加入了android:launchMode="singleTask"
得在UI线程里调用execute；在onCreate中调用，onPostExecute是不执行的。
android-support-v4.jar低版本下，在FragmentActivity下调用，onPostExecute是不执行的。
关键在MAINActivity onCreate中添加
try {
Class.forName("android.os.AsyncTask");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
以下是案例，有关HTTP请求，需要加入gson.jar
package com.example.asynctasktest;import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.view.View.OnClickListener;public class MainActivity extends Activity {private Button button; private ProgressBar progressBar; private TextView textView; @Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);button = (Button)findViewById(R.id.button03); progressBar = (ProgressBar)findViewById(R.id.progressBar02); textView = (TextView)findViewById(R.id.textView01); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { startGetArea();} }); ProgressBarAsyncTask asyncTask = new ProgressBarAsyncTask(textView, progressBar); asyncTask.execute("http://www.xxx.com/getAreaList.htm");}public void startGetArea(){Message msg = mhandler.obtainMessage();msg.what = 1;mhandler.sendMessage(msg);}/*** handler处理消息机制*/protected Handler mhandler = new Handler() {public void handleMessage(Message message) {switch (message.what) {case 1:new ProgressBarAsyncTask(textView, progressBar).execute("http://www.xxx.com/getAreaList.htm");break;}}};@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.main, menu);return true;}}package com.example.asynctasktest;import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;import org.apache.http.HttpEntity;
import org.apache.http.util.EntityUtils;import android.os.AsyncTask;
import android.util.Log;
import android.widget.ProgressBar;
import android.widget.TextView;import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;/** * 生成该类的对象，并调用execute方法之后 * 首先执行的是onProExecute方法 * 其次执行doInBackgroup方法 * */
public class ProgressBarAsyncTask extends AsyncTask<String, Integer, List<AllArea>> { private TextView textView; private ProgressBar progressBar; private static Gson gson = new GsonBuilder().setVersion(1).create();List<String> listnames = new ArrayList<String>();List<String> listid = new ArrayList<String>();public ProgressBarAsyncTask(TextView textView, ProgressBar progressBar) { super(); this.textView = textView; this.progressBar = progressBar; } /** * 这里的String参数对应AsyncTask中的第一个参数 * 这里的List<AllArea>返回值对应AsyncTask的第三个参数 * 该方法并不运行在UI线程当中，主要用于异步操作，所有在该方法中不能对UI当中的空间进行设置和修改 * 但是可以调用publishProgress方法触发onProgressUpdate对UI进行操作 */@Overrideprotected List<AllArea> doInBackground(String... params) {// TODO Auto-generated method stubList<AllArea> areaList = null;HttpEntity entity;try {entity = HttpUtil.send(HttpUtil.METHOD_GET, params[0], null);String json=EntityUtils.toString(entity);Type type = new TypeToken<List<AllArea>>() {}.getType();areaList = gson.fromJson(json, type);} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}return areaList;}/** * 这里的String参数对应AsyncTask中的第三个参数（也就是接收doInBackground的返回值） * 在doInBackground方法执行结束之后在运行，并且运行在UI线程当中 可以对UI空间进行设置 */ @Overrideprotected void onPostExecute(List<AllArea> result) {// TODO Auto-generated method stubsuper.onPostExecute(result);textView.setText("异步操作执行结束" + result);if(result == null){Log.e("", "result == null");}else{Log.e("", "result != null"+result.size());for(int i = 0;i<result.size();i++){listnames.add(result.get(i).getIndustryName());listid.add(result.get(i).getId()+"");}}}/*** 该方法运行在UI线程当中,并且运行在UI线程当中 可以对UI空间进行设置 */@Override protected void onPreExecute() { textView.setText("开始执行异步线程"); } /** * 这里的Intege参数对应AsyncTask中的第二个参数 * 在doInBackground方法当中，，每次调用publishProgress方法都会触发onProgressUpdate执行 * onProgressUpdate是在UI线程中执行，所有可以对UI空间进行操作 */ @Override protected void onProgressUpdate(Integer... values) { int vlaue = values[0]; progressBar.setProgress(vlaue); }
} package com.example.asynctasktest;import java.util.ArrayList;import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;import android.util.Log;/*** HTTP请求方式类* @author Administrator**/
public class HttpUtil {public static final int METHOD_GET=0;public static final int METHOD_POST=1;/*** * @param method GET请求* @param url 请求路径* @param pairs 提交参数* @return* @throws Exception*/public static HttpEntity send(int method,String url,ArrayList<NameValuePair> pairs)throws Exception{HttpClient client=new DefaultHttpClient();HttpResponse resp=null;switch(method){case METHOD_GET:Log.i("send", url);HttpGet get=new HttpGet(url);resp=client.execute(get);Log.i("send", resp.toString());break;case METHOD_POST:HttpPost post=new HttpPost(url);HttpEntity entity=new UrlEncodedFormEntity(pairs,"utf-8");post.setEntity(entity);post.setHeader("Content-Type", "x-www-form-urlencoded");resp=client.execute(post);break;}return resp.getEntity();}
}
package com.example.asynctasktest;import java.io.Serializable;public class AllArea implements Serializable{/*** */private static final long serialVersionUID = -8325422695071123262L;private int id;private int type;private int parentId;private String areaName;private String areaNo;public int getId() {return id;}public void setId(int id) {this.id = id;}public int getType() {return type;}public void setType(int type) {this.type = type;}public int getParentId() {return parentId;}public void setParentId(int parentId) {this.parentId = parentId;}public String getIndustryName() {return areaName;}public void setIndustryName(String industryName) {this.areaName = industryName;}public String getIndustryDesc() {return areaNo;}public void setIndustryDesc(String industryDesc) {this.areaNo = industryDesc;}}[{"state":1,"type":1,"seq":1,"parentId":1,"areaNo":"3601","areaName”:”东城区”,”id”:11},{“state":1,"type":1,"seq":2,"parentId":1,"areaNo":"3602","areaName”:”西城区”,”id”:22},{“state":1,"type":1,"seq":3,"parentId":1,"areaNo":"3603","areaName”:”海淀区”,”id”:33},{“state":1,"type":1,"seq":4,"parentId":1,"areaNo":"3604","areaName”:”朝阳区”,”id”:44},{“state":1,"type":1,"seq":5,"parentId":1,"areaNo":"3605","areaName”:”昌平区”,”id”:55},{“state":1,"type":1,"seq":6,"parentId":1,"areaNo":"3606","areaName”:”丰台区”,”id”:66}]
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