嗨，我需要帮助，我已经完成了一个应用程序与苹果rss饲料中的前10个下载应用程序，我陷入困境，以避免每次设备旋转时下载数据，方法是获取URL的值和限制onCreate methoud
我已经实现了这个并将数据保存在onSaveInstanceState中，但它会继续在设备上下载数据
这是我的MainActivity代码
package com.ksamj.top10downloader;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private ListView listApps;
private String feedURL = "http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=%d/xml";
private int feedLimit = 10;
private String feedCachedURL = "INVALID";
public static final String STATE_URL = "feedURL";
public static final String STATE_LIMIT = "feedLimit";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listApps = (ListView) findViewById(R.id.xmlListView);
if(savedInstanceState != null) // if null means run at 1st time
{
feedURL = savedInstanceState.getString(STATE_URL);
feedLimit = savedInstanceState.getInt(STATE_LIMIT);
Log.d(TAG, "from Bundle feedURL: "+ feedURL);
Log.d(TAG, "from Bundle feedLimit: "+ feedLimit);
}
downloadURL(String.format(feedURL,feedLimit));
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.feed_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menuFreeApps:
feedURL = "http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=%d/xml";
break;
case R.id.menuPaidApps:
feedURL = "http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/toppaidapplications/limit=%d/xml";
break;
case R.id.menuSongs:
feedURL = "http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topsongs/limit=%d/xml";
break;
case R.id.menu10:
feedLimit = 10;
item.setChecked(true);
break;
case R.id.menu25:
feedLimit = 25;
item.setChecked(true);
break;
case R.id.menuRefresh:
feedCachedURL = "INVALID";
break;
default:
return super.onOptionsItemSelected(item);
}
downloadURL(String.format(feedURL,feedLimit));
return true;
}
@Override
protected void onSaveInstanceState(Bundle outState) {
outState.putString(STATE_URL, feedURL);
outState.putInt(STATE_LIMIT, feedLimit);
super.onSaveInstanceState(outState);
}
private void downloadURL(String feedURL) {
if (!feedURL.equalsIgnoreCase(feedCachedURL)) {
Log.d(TAG, "downloadURL: Downloading...");
DownloadData downloadData = new DownloadData();
downloadData.execute(feedURL);
feedCachedURL = feedURL;
Log.d(TAG, "downloadURL: feedURL " + feedURL);
Log.d(TAG, "downloadURL: feedCachedURL " + feedCachedURL);
}else
Log.d(TAG, "downloadURL: Nothing to Download");
}
private class DownloadData extends AsyncTask<String, Void, String> {
private static final String TAG = "DownloadData";
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
//Log.d(TAG, "onPostExecute: params are" + s);
ParseApplications parseApplications = new ParseApplications();
parseApplications.parse(s);
FeedAdapter feedAdapter = new FeedAdapter(MainActivity.this, R.layout.list_record, parseApplications.getApplications());
listApps.setAdapter(feedAdapter);
}
@Override
protected String doInBackground(String... strings) {
Log.d(TAG, "doInBackground: starts with " + strings[0]);
String rssFeed = downloadXML(strings[0]);
if (rssFeed == null) {
Log.e(TAG, "doInBackground: Error Downloading");
}
return rssFeed;
}
private String downloadXML(String urlPath) {
StringBuilder xmlResult = new StringBuilder();
try {
URL url = new URL(urlPath);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
int response = httpURLConnection.getResponseCode();
Log.d(TAG, "downloadXML: The response Code is " + response);
BufferedReader reader = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));
int charsRead;
char[] inputBuffer = new char[5500];
while (true) {
charsRead = reader.read(inputBuffer);
if (charsRead < 0)
break;
if (charsRead > 0)
xmlResult.append(String.copyValueOf(inputBuffer, 0, charsRead));
}
reader.close();
return xmlResult.toString();
} catch (MalformedURLException ex) {
Log.e(TAG, "downloadXML: Malformated URL Exp: " + ex.getMessage());
} catch (IOException ex) {
Log.e(TAG, "downloadXML: IO Exp: " + ex.getMessage());
}
return null;
}
}
}
这是我的logcat，用于执行后的简单旋转
03-28 10:01:56.373 21047-21047/com.ksamj.top10downloader W/art: Verification of java.lang.Object com.ksamj.top10downloader.MainActivity.access$super(com.ksamj.top10downloader.MainActivity, java.lang.String, java.lang.Object[]) took 100.789ms
03-28 10:01:56.515 21047-21047/com.ksamj.top10downloader W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
03-28 10:01:56.805 21047-21047/com.ksamj.top10downloader D/MainActivity: downloadURL: Downloading...
03-28 10:01:56.809 21047-21047/com.ksamj.top10downloader D/MainActivity: downloadURL: feedURL http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=10/xml
03-28 10:01:56.809 21047-21047/com.ksamj.top10downloader D/MainActivity: downloadURL: feedCachedURL http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=10/xml
03-28 10:01:56.809 21047-21272/com.ksamj.top10downloader D/DownloadData: doInBackground: starts with http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=10/xml
03-28 10:01:56.813 21047-21272/com.ksamj.top10downloader D/NetworkSecurityConfig: No Network Security Config specified, using platform default
03-28 10:01:56.953 21047-21274/com.ksamj.top10downloader I/OpenGLRenderer: Initialized EGL, version 1.4
03-28 10:01:56.953 21047-21274/com.ksamj.top10downloader D/OpenGLRenderer: Swap behavior 1
03-28 10:01:56.957 21047-21274/com.ksamj.top10downloader W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
03-28 10:01:56.957 21047-21274/com.ksamj.top10downloader D/OpenGLRenderer: Swap behavior 0
03-28 10:01:57.002 21047-21272/com.ksamj.top10downloader D/DownloadData: downloadXML: The response Code is 200
03-28 10:01:57.098 21047-21047/com.ksamj.top10downloader W/art: Before Android 4.1, method int android.support.v7.widget.ListViewCompat.lookForSelectablePosition(int, boolean) would have incorrectly overridden the package-private method in android.widget.ListView
03-28 10:01:57.403 21047-21047/com.ksamj.top10downloader W/InputMethodManager: Ignoring onBind: cur seq=94, given seq=93
03-28 10:02:02.331 21047-21047/com.ksamj.top10downloader D/MainActivity: from Bundle feedURL: http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=%d/xml
03-28 10:02:02.332 21047-21047/com.ksamj.top10downloader D/MainActivity: from Bundle feedLimit: 10
03-28 10:02:02.332 21047-21047/com.ksamj.top10downloader D/MainActivity: downloadURL: Downloading...
03-28 10:02:02.333 21047-21047/com.ksamj.top10downloader D/MainActivity: downloadURL: feedURL http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=10/xml
03-28 10:02:02.333 21047-21047/com.ksamj.top10downloader D/MainActivity: downloadURL: feedCachedURL http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=10/xml
03-28 10:02:02.336 21047-21345/com.ksamj.top10downloader D/DownloadData: doInBackground: starts with http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=10/xml
03-28 10:02:02.354 21047-21345/com.ksamj.top10downloader D/DownloadData: downloadXML: The response Code is 200
你可以帮助确定我在做错了什么或错过了吗？
答案 0 :(得分：1)
使用Loader模式。加载器允许您注册异步进程，以便您不启动其他任务，因此完成时存在的活动将获得实际结果。有关详细信息，请参阅https://developer.android.com/reference/android/app/LoaderManager.html。
答案 1 :(得分：0)
每次将设备feedCachedURL变量设置为INVALID时，您都应该在旋转之前将其保存
答案 2 :(得分：-1)
当savedInstance为null时，只需调用downloadUrl函数。 定义一个变量rssFeed，您将获得异步任务的onPstExecute。
FileInputStream此外，您需要保存您在OnSavedInstanceMethod中获得的Feed，并在postExecute中设置mRssFeed。
private String mRssFeed;
if(savedInstanceState != null) // if null means run at 1st time
{
feedURL = savedInstanceState.getString(STATE_URL);
feedLimit = savedInstanceState.getInt(STATE_LIMIT);
Log.d(TAG, "from Bundle feedURL: "+ feedURL);
Log.d(TAG, "from Bundle feedLimit: "+ feedLimit);
mRssFeed = savedInstanceState.getString("RSS_FEED");
if(mRssFeed != null && !mRssFeed.equals(""){
ParseApplications parseApplications = new ParseApplications();
parseApplications.parse(mRssFeed);
FeedAdapter feedAdapter = new FeedAdapter(MainActivity.this, R.layout.list_record, parseApplications.getApplications());
listApps.setAdapter(feedAdapter);
}else{
downloadURL(String.format(feedURL,feedLimit));
}
}else{
downloadURL(String.format(feedURL,feedLimit));
}
即使您从savedInstance恢复数据，您的downloadUrl也会被调用。把它放在其他地方将确保不会调用它。
但正如加布所说，如果你处于下载中间并且状态发生变化，可能会出现一些问题。在这种情况下，我建议你进一步使用RxAndroid。与AsyncTasks相比，这为您提供了很多控制。
以下是关于android中一些最好的异步编程实践的好读物：
http://code.hootsuite.com/asynchronous-android-programming-the-good-the-bad-and-the-ugly/