我创建应用程序，使用jsonParser.makeHttpRequest检查数据库的登录信息 我尝试让我的应用程序在10秒后停止，以防没有互联网连接或服务器没有响应。然而，当登录按钮第二次点击应用程序崩溃时，代码会工作 任何人都可以支持为什么会发生这种情况
请参阅以下代码
package com.example.pfms;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.conn.ConnectTimeoutException;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;
public class MainActivity extends Activity {
private String id,pass,p,logincheck;
private EditText username,password;
private Button login;
private CheckLogin cl;
private ProgressDialog pDialog;
private SharedPreferences prefs;
JSONParser jsonParser = new JSONParser();
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCT = "product";
private static final String url = "http://192.168.1.11/pfm/get_id.php";
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
cl= new CheckLogin();
username=(EditText)findViewById(R.id.editText1);
password=(EditText)findViewById(R.id.editText2);
login=(Button)findViewById(R.id.button1);
prefs = this.getSharedPreferences("com.example.pfms", MODE_PRIVATE);
logincheck=prefs.getString("com.example.pfms.login", "0");
if(!logincheck.equals("0")){
Intent i=new Intent(MainActivity.this,TechOption.class);
Bundle info=new Bundle();
info.putString("techid",logincheck);
i.putExtras(info);
startActivity(i);
}
login.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
cl.execute();
}
});
}
class CheckLogin extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Checking Login info. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
p="0";
pass="0";
Log.d("test", "dialog");
}
/**
* Getting product details in background thread
* */
protected String doInBackground(String... params) {
// updating UI from Background Thread
// runOnUiThread(new Runnable() {
// public void run() {
// Check for success tag
int success;
try {
Log.d("test", "run");
// Building Parameters
List<NameValuePair> params2 = new ArrayList<NameValuePair>();
id=username.getText().toString();
pass=password.getText().toString();
params2.add(new BasicNameValuePair("id",id));
// getting product details by making HTTP request
// Note that product details url will use GET request
// HttpParams httpParameters = new BasicHttpParams();
// HttpConnectionParams.setConnectionTimeout(httpParameters, 30000);
// HttpConnectionParams.setSoTimeout(httpParameters, 30000);
// DefaultHttpClient httpClient = new DefaultHttpClient(httpParameters);
messageHandler.sendEmptyMessageDelayed(0, 10000);
Log.d("test", "before");
JSONObject json = jsonParser.makeHttpRequest(
url, "GET", params2);
// check your log for json response
Log.d("Single Product Details", json.toString());
// json success tag
success = json.getInt(TAG_SUCCESS);
Log.d("test", "before success");
if (success == 1) {
// successfully received product details
JSONArray actiondetail = json
.getJSONArray(TAG_PRODUCT); // JSON Array
// get first product object from JSON Array
JSONObject c = actiondetail.getJSONObject(0);
// Storing each json item in variable
p="";
p = c.getString("pass");
Log.d("info", "p="+p);
Log.d("info", "pass="+pass);
}else{
Toast.makeText(getBaseContext(), "Wrong Username", Toast.LENGTH_LONG).show();
}
Log.d("test", "after success");
} catch (JSONException e) {
//pDialog.dismiss();
//Toast.makeText(getBaseContext(), "Please check internet connection", Toast.LENGTH_LONG).show();
e.printStackTrace();
}
// }
// });
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog once got all details
pDialog.dismiss();
Log.d("test", "dismiss dailog");
if(p.contentEquals(pass)){
Intent i=new Intent(MainActivity.this,TechOption.class);
Bundle info=new Bundle();
info.putString("techid",id);
i.putExtras(info);
SharedPreferences.Editor editor = prefs.edit();
editor.putString("com.example.pfms.login",id);
editor.commit();
startActivity(i);
}
else{
Toast.makeText(getBaseContext(), "Wrong Password", Toast.LENGTH_LONG).show();
}
}
}
private Handler messageHandler = new Handler() {
public void handleMessage(Message msg) {
super.handleMessage(msg);
pDialog.dismiss();
Toast.makeText(getBaseContext(), "Please check internet connection", Toast.LENGTH_LONG).show();
cl.cancel(true);
}
};
}
请参阅以下错误：
11-05 09:37:09.053: D/AndroidRuntime(1398): Shutting down VM
11-05 09:37:09.053: W/dalvikvm(1398): threadid=1: thread exiting with uncaught exception (group=0x41465700)
11-05 09:37:09.123: E/AndroidRuntime(1398): FATAL EXCEPTION: main
11-05 09:37:09.123: E/AndroidRuntime(1398): java.lang.IllegalStateException: Cannot execute task: the task is already running.
11-05 09:37:09.123: E/AndroidRuntime(1398): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:575)
11-05 09:37:09.123: E/AndroidRuntime(1398): at android.os.AsyncTask.execute(AsyncTask.java:534)
11-05 09:37:09.123: E/AndroidRuntime(1398): at com.example.pfms.MainActivity$2.onClick(MainActivity.java:79)
11-05 09:37:09.123: E/AndroidRuntime(1398): at android.view.View.performClick(View.java:4240)
11-05 09:37:09.123: E/AndroidRuntime(1398): at android.view.View$PerformClick.run(View.java:17721)
11-05 09:37:09.123: E/AndroidRuntime(1398): at android.os.Handler.handleCallback(Handler.java:730)
11-05 09:37:09.123: E/AndroidRuntime(1398): at android.os.Handler.dispatchMessage(Handler.java:92)
11-05 09:37:09.123: E/AndroidRuntime(1398): at android.os.Looper.loop(Looper.java:137)
11-05 09:37:09.123: E/AndroidRuntime(1398): at android.app.ActivityThread.main(ActivityThread.java:5103)
11-05 09:37:09.123: E/AndroidRuntime(1398): at java.lang.reflect.Method.invokeNative(Native Method)
11-05 09:37:09.123: E/AndroidRuntime(1398): at java.lang.reflect.Method.invoke(Method.java:525)
11-05 09:37:09.123: E/AndroidRuntime(1398): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-05 09:37:09.123: E/AndroidRuntime(1398): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-05 09:37:09.123: E/AndroidRuntime(1398): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
AsyncTask的对象只能运行一次。这就是为什么你得到 IllegalStateException 。
从onCreate（）中删除对象实例化[cl= new CheckLogin()]。
相反，
login.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
new CheckLogin.execute(); // creating an anonymous object of the AsyncTask makes sure that you never use it again which prevents any IllegalStateExceptions
}
});