使用异步任务制作进度对话框
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【中文标题】使用异步任务制作进度对话框【英文标题】：making a ProgressDialog with Asynch task 【发布时间】：2012-04-17 09:12:48 【问题描述】：我正在尝试在异步任务中获取我的代码，只有我的应用程序不断崩溃，有人可以找出导致此错误的原因（我认为 NullPointerException）。老实说，我只是从另一个问题中复制了一些代码并将所有内容都放入其中。
package net.thinkbin;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
public class entertainment extends ListActivity
private static final String TITLE = "Title";
private static final String AUTHOR = "Author";
private static final String VIEWS = "Views";
private static final String RATES = "Rates";
private static final String CONTENT = "Content";
JSONArray ideas = null;
@Override
protected void onCreate(Bundle savedInstanceState)
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.listplaceholder3);
new DoInBackgrd().execute();
Button view = (Button) findViewById(R.id.button1);
view.setOnClickListener(new View.OnClickListener()
public void onClick(View v)
// TODO Auto-generated method stub
startActivity(new Intent("net.thinkbin.TUTORIAL1"));
overridePendingTransition(0, 0);
finish();
);
Button share = (Button) findViewById(R.id.button2);
share.setOnClickListener(new View.OnClickListener()
public void onClick(View v)
// TODO Auto-generated method stub
startActivity(new Intent("net.thinkbin.SHARE"));
overridePendingTransition(0, 0);
finish();
);
Button menu = (Button) findViewById(R.id.buttonhome);
menu.setOnClickListener(new View.OnClickListener()
public void onClick(View v)
// TODO Auto-generated method stub
startActivity(new Intent("net.thinkbin.MENU"));
overridePendingTransition(0, 0);
finish();
);
private class DoInBackgrd extends AsyncTask<Void, Void, Void> implements
DialogInterface.OnCancelListener
private ProgressDialog processDialog;
@Override
protected void onPreExecute()
ProgressDialog.show(entertainment.this, "", "Loading...");
processDialog.setCancelable(true);
public void onCancel(DialogInterface arg0)
// TODO Auto-generated method stub
if (processDialog.isShowing())
processDialog.dismiss();
@Override
protected Void doInBackground(Void... arg0)
// TODO Auto-generated method stub
ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
JSONObject json = JSONfunctions.getJSONfromURL("http://www.thinkbin.net/include/api/index.php?cat=Entertainment&type=Views&i=10");
try
ideas = json.getJSONArray("Ideas");
// looping through All Contacts
for(int i = 0; i < ideas.length(); i++)
JSONObject c = ideas.getJSONObject(i);
// Storing each json item in variable
String title = c.getString(TITLE);
String author = c.getString(AUTHOR);
String views = c.getString(VIEWS);
String rates = c.getString(RATES);
String content = c.getString(CONTENT);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TITLE, "Title: " + title);
map.put(AUTHOR, "Author: " + author);
map.put(VIEWS, "Views: " + views);
map.put(RATES, "Rates: " + rates);
map.put(CONTENT, content);
// adding HashList to ArrayList
mylist.add(map);
catch(JSONException e)
Log.e("log_tag", "Error parsing data "+e.toString());
ListAdapter adapter = new SimpleAdapter(entertainment.this, mylist , R.layout.main2,
new String[] TITLE, AUTHOR, VIEWS, RATES, CONTENT ,
new int[] R.id.item_title, R.id.item_subtitle, R.id.item3, R.id.item4, R.id.item5 );
setListAdapter(adapter);
//selecting single ListView item
ListView lv = getListView();
//Launching new screen on Selecting Single ListItem
lv.setOnItemClickListener(new OnItemClickListener()
public void onItemClick(AdapterView<?> parent, View view,
int position, long id)
// getting values from selected ListItem
String Title2 = ((TextView) view.findViewById(R.id.item_title)).getText().toString();
String Author2 = ((TextView) view.findViewById(R.id.item_subtitle)).getText().toString();
String Content2 = ((TextView) view.findViewById(R.id.item5)).getText().toString();
Intent in = new Intent(getApplicationContext(), idea.class);
overridePendingTransition(0, 0);
in.putExtra(TITLE, Title2);
in.putExtra(AUTHOR, Author2);
in.putExtra(CONTENT, Content2);
startActivity(in);
);
return null;
@Override
protected void onPostExecute(Void unused)
if (processDialog.isShowing())
processDialog.dismiss();
日志猫：
04-03 15:56:43.988: D/dalvikvm(324): GC_EXTERNAL_ALLOC freed 48K, 53% free 2552K/5379K, external 1625K/2137K, paused 189ms
04-03 15:56:48.768: D/dalvikvm(324): GC_EXTERNAL_ALLOC freed 7K, 53% free 2570K/5379K, external 3086K/3528K, paused 33ms
04-03 15:56:48.878: D/dalvikvm(324): GC_EXTERNAL_ALLOC freed 1K, 53% free 2571K/5379K, external 4286K/5352K, paused 39ms
04-03 15:59:07.597: D/dalvikvm(324): GC_CONCURRENT freed 958K, 53% free 3162K/6727K, external 5965K/6851K, paused 3ms+4ms
04-03 16:51:19.427: D/dalvikvm(362): GC_EXTERNAL_ALLOC freed 49K, 53% free 2552K/5379K, external 1625K/2137K, paused 48ms
04-03 16:51:24.338: D/dalvikvm(362): GC_EXTERNAL_ALLOC freed 7K, 53% free 2571K/5379K, external 3086K/3528K, paused 40ms
04-03 16:51:24.448: D/dalvikvm(362): GC_EXTERNAL_ALLOC freed 1K, 53% free 2572K/5379K, external 4286K/5352K, paused 41ms
04-03 16:51:28.468: D/AndroidRuntime(362): Shutting down VM
04-03 16:51:28.468: W/dalvikvm(362): threadid=1: thread exiting with uncaught exception (group=0x40015560)
04-03 16:51:28.478: E/AndroidRuntime(362): FATAL EXCEPTION: main
04-03 16:51:28.478: E/AndroidRuntime(362): java.lang.RuntimeException: Unable to start activity ComponentInfonet.thinkbin/net.thinkbin.entertainment: java.lang.NullPointerException
04-03 16:51:28.478: E/AndroidRuntime(362): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.os.Handler.dispatchMessage(Handler.java:99)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.os.Looper.loop(Looper.java:123)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.app.ActivityThread.main(ActivityThread.java:3683)
04-03 16:51:28.478: E/AndroidRuntime(362): at java.lang.reflect.Method.invokeNative(Native Method)
04-03 16:51:28.478: E/AndroidRuntime(362): at java.lang.reflect.Method.invoke(Method.java:507)
04-03 16:51:28.478: E/AndroidRuntime(362): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-03 16:51:28.478: E/AndroidRuntime(362): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-03 16:51:28.478: E/AndroidRuntime(362): at dalvik.system.NativeStart.main(Native Method)
04-03 16:51:28.478: E/AndroidRuntime(362): Caused by: java.lang.NullPointerException
04-03 16:51:28.478: E/AndroidRuntime(362): at net.thinkbin.entertainment$DoInBackgrd.onPreExecute(entertainment.java:92)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.os.AsyncTask.execute(AsyncTask.java:391)
04-03 16:51:28.478: E/AndroidRuntime(362): at net.thinkbin.entertainment.onCreate(entertainment.java:43)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-03 16:51:28.478: E/AndroidRuntime(362): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
04-03 16:51:28.478: E/AndroidRuntime(362): ... 11 more
04-03 16:52:48.988: D/dalvikvm(397): GC_EXTERNAL_ALLOC freed 50K, 53% free 2552K/5379K, external 1625K/2137K, paused 134ms
04-03 16:52:53.798: D/dalvikvm(397): GC_EXTERNAL_ALLOC freed 7K, 53% free 2571K/5379K, external 3086K/3528K, paused 35ms
04-03 16:52:53.909: D/dalvikvm(397): GC_EXTERNAL_ALLOC freed 1K, 53% free 2572K/5379K, external 4286K/5352K, paused 42ms
04-03 16:52:57.827: D/AndroidRuntime(397): Shutting down VM
04-03 16:52:57.827: W/dalvikvm(397): threadid=1: thread exiting with uncaught exception (group=0x40015560)
04-03 16:52:57.837: E/AndroidRuntime(397): FATAL EXCEPTION: main
04-03 16:52:57.837: E/AndroidRuntime(397): java.lang.RuntimeException: Unable to start activity ComponentInfonet.thinkbin/net.thinkbin.entertainment: java.lang.NullPointerException
04-03 16:52:57.837: E/AndroidRuntime(397): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.os.Handler.dispatchMessage(Handler.java:99)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.os.Looper.loop(Looper.java:123)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.app.ActivityThread.main(ActivityThread.java:3683)
04-03 16:52:57.837: E/AndroidRuntime(397): at java.lang.reflect.Method.invokeNative(Native Method)
04-03 16:52:57.837: E/AndroidRuntime(397): at java.lang.reflect.Method.invoke(Method.java:507)
04-03 16:52:57.837: E/AndroidRuntime(397): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-03 16:52:57.837: E/AndroidRuntime(397): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-03 16:52:57.837: E/AndroidRuntime(397): at dalvik.system.NativeStart.main(Native Method)
04-03 16:52:57.837: E/AndroidRuntime(397): Caused by: java.lang.NullPointerException
04-03 16:52:57.837: E/AndroidRuntime(397): at net.thinkbin.entertainment$DoInBackgrd.onPreExecute(entertainment.java:92)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.os.AsyncTask.execute(AsyncTask.java:391)
04-03 16:52:57.837: E/AndroidRuntime(397): at net.thinkbin.entertainment.onCreate(entertainment.java:43)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-03 16:52:57.837: E/AndroidRuntime(397): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
04-03 16:52:57.837: E/AndroidRuntime(397): ... 11 more
04-03 16:52:59.357: I/Process(397): Sending signal. PID: 397 SIG: 9
04-03 17:08:38.488: D/dalvikvm(434): GC_EXTERNAL_ALLOC freed 51K, 53% free 2552K/5379K, external 1625K/2137K, paused 78ms
04-03 17:08:43.277: D/dalvikvm(434): GC_EXTERNAL_ALLOC freed 7K, 53% free 2571K/5379K, external 3086K/3528K, paused 34ms
04-03 17:08:43.397: D/dalvikvm(434): GC_EXTERNAL_ALLOC freed 1K, 53% free 2572K/5379K, external 4286K/5352K, paused 41ms
04-03 17:08:48.317: D/dalvikvm(434): GC_CONCURRENT freed 959K, 53% free 3163K/6727K, external 5965K/6851K, paused 4ms+4ms
04-03 17:09:00.288: D/dalvikvm(434): GC_CONCURRENT freed 1260K, 50% free 3974K/7879K, external 4533K/5704K, paused 4ms+7ms
【问题讨论】：
当错误出现时总是在这里发布完整的 logcat...entertainment.java see line no.92，这是？
processDialog.setCancelable(true);
看我的答案你忘了分配...
【参考方案1】：
@Override
protected void onPreExecute()
processDialog = ProgressDialog.show(entertainment.this, "", "Loading...");
processDialog.setCancelable(true);
【讨论】：
【参考方案2】：processDialog 为空，因为它尚未在您的 preexecute 方法中正确初始化...
【讨论】：
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