【发布时间】：2012-03-09 08:29:45
【问题描述】：
经过几天的绝望，我终于创建了几乎可以工作的例子。
目标：在 onCreate 我想在 AsyncTask 中下载和解析 XML 文件，显示进度对话框，更新 UI 并关闭对话框。
问题： 当方向改变时，Activity 重新启动并且 AsyncTask 失去对它的引用。有很多关于它的问题和博客。但我不知道为什么这个特定的解决方案不起作用。或者在这种情况下android如何处理对话框。
状态：当我启动一个应用程序时一切正常。我可以旋转设备，我可以通过菜单再次手动启动任务。但是在任务完成后，我再次更改方向弹出对话框（如预期的那样）并且没有其他任何事情发生。没有进度变化，没有对话框关闭。 AsyncTask 正常结束。
代码：
package com.test;
import java.io.*;
import java.net.URL;
import java.net.URLConnection;
import java.util.*;
public class Test extends TabActivity {
DownloadFileAsync task;
ProgressDialog progressDialog;
static final int PROGRESS_DIALOG = 0;
private static Data data;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
/* - Run from different locations bug - */
//http://code.google.com/p/android/issues/detail?id=2373
if (!isTaskRoot()) {
final Intent intent = getIntent();
final String intentAction = intent.getAction();
if (intent.hasCategory(Intent.CATEGORY_LAUNCHER) &&
intentAction != null && intentAction.equals(Intent.ACTION_MAIN)) {
finish();
}
}
/* - /Run from different locations bug */
/* -------------- Tabs ---------------- */
Resources res = getResources();
TabHost mTabHost = getTabHost();
mTabHost.addTab(mTabHost.newTabSpec("overview").setIndicator("MYTAB1",res.getDrawable(R.drawable.ic_tab_home)).setContent(R.id.tab1));
mTabHost.setCurrentTab(0);
/* -------------- /Tabs --------------- */
/* -------------- /Data --------------- */
task = (DownloadFileAsync)getLastNonConfigurationInstance();
if(task!= null) {
task.setActivity(this);
} else {
if(data == null) {
File datafile = this.getFileStreamPath("data.dat");
if(datafile.exists()){
//Log.d("log", "File exists!");
try {
long time = System.currentTimeMillis();
ObjectInputStream obj = new ObjectInputStream(new FileInputStream(datafile));
data = (Data)obj.readObject();
obj.close();
Log.d("time", "loaded in:"+(System.currentTimeMillis()- time));
if(data.isUpToDate() || !isOnline()){
update();
}
} catch (Exception e) {
e.printStackTrace();
datafile.delete();
data = null;
}
//Log.d("log", "Passed?");
}
}
/* DEBUG if(data == null || !data.isUpToDate())*/ this.synchronize();
}
/* -------------- /Data --------------- */
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
menu.add("Synchronize").setIcon(R.drawable.ic_menu_refresh);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
synchronize();
return super.onOptionsItemSelected(item);
}
@Override
public Object onRetainNonConfigurationInstance() {
if(task != null) task.setActivity(null);
return(task);
}
protected Dialog onCreateDialog(int id) {
switch (id) {
case PROGRESS_DIALOG:
progressDialog = new ProgressDialog(this);
progressDialog.setMessage("Aktualizuji ...");
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.setCancelable(false);
//progressDialog.show();
return progressDialog;
default:
return null;
}
}
public void update() {
}
private void onTaskCompleted() {
task = null;
dismissDialog(PROGRESS_DIALOG);
Log.d("tok","Task.onComplete");
update();
}
public void synchronize(){
if(isOnline()) {
showDialog(PROGRESS_DIALOG);
progressDialog.setProgress(0); // <-- this is the last time progressDialog updates
task = new DownloadFileAsync(this);
task.execute();
}
}
public boolean isOnline() {
ConnectivityManager cm =
(ConnectivityManager) getSystemService(WaspActivity.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
if (netInfo != null && netInfo.isConnectedOrConnecting()) {
return true;
}
return false;
}
private static class DownloadFileAsync extends AsyncTask<String, String, String> {
private Data tempData;
private Test activity;
private int progress = 0;
private File metafile;
private File tempDir;
private FileOutputStream fos;
public DownloadFileAsync(Test activity) {
this.setActivity(activity);
... some more init ...
}
public void setActivity(Test activity) {
this.activity = activity;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
tempData = new Data();
}
@Override
protected String doInBackground(String... aurl) {
try {
... some heavy load ...
//this.progress = someValue;
} catch (Exception e) {
Log.d("Error", "Error while processing files. Code:"+e.getMessage());
e.printStackTrace();
}
//Log.d("time","Task "+(System.currentTimeMillis() - time));
return null;
}
protected void onProgressUpdate(String... progress) {
if(activity != null) activity.progressDialog.setProgress(this.progress);
}
@Override
protected void onPostExecute(String unused) {
data = tempData;
tempData = null;
if(activity != null) {
activity.onTaskCompleted();
activity = null;
}
}
}
}
【问题讨论】：
-
看here。你可以在那里找到你的问题的答案。这是一个非常优雅的解决方案。
-
查看我关于这个主题的帖子：Handling Configuration Changes with
Fragments
标签： android android-asynctask progressdialog android-orientation