【发布时间】：2017-04-13 02:46:17
【问题描述】：
我创建了一个简单的 android 应用程序，它只解析来自苹果网站的 XML。 它具有解析前 10 名“歌曲”、“付费应用程序”或“免费应用程序”的菜单。
对于网络通话，我使用 volley。现在，当我在旋转设备时看到日志时，processXml()（从 URL 获取 xml 并将其放在列表视图中）多次调用，在 onCreate() 和 onRestoreInstanceState() 中。恕我直言，这可能是多余的下载。
我的问题：
- 我是否将 processXml() 放在了错误的位置？如果是这样，避免冗余网络调用的正确位置在哪里？
- 既然我使用了volley，有没有办法缓存响应并在设备旋转时使用它？我想我在 VolleySingleton 上写了缓存，但我不知道我的实现是否正确
非常感谢
这是日志
// start of app
04-13 09:14:36.456 MainActivity: onCreate: processXml() called
// select "songs" from menu
04-13 09:14:49.627 MainActivity: onOptionsItemSelected: processXml() called
// rotate device
04-13 09:14:55.758 MainActivity: onCreate: processXml() called
这是我在 MainACtivity.java 上的源代码 公共类 MainActivity 扩展 AppCompatActivity {
private static final String TAG = "MainActivity";
private static final String KEY_RSS_URL = "KEY_RSS_URL";
private static final String KEY_FEED_LIMIT = "KEY_FEED_LIMIT";
private String rssUrl = "http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=%d/xml";
private int feedLimit = 10;
private ListView xmlListView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.xmlListView = (ListView) findViewById(R.id.xmlListView);
if (savedInstanceState != null) {
this.rssUrl = savedInstanceState.getString(KEY_RSS_URL);
this.feedLimit = savedInstanceState.getInt(KEY_FEED_LIMIT);
}
// need to put it here because when app start, it should already display top 10 free aps
processRss(String.format(this.rssUrl, this.feedLimit));
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
... create menu
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int itemId = item.getItemId();
switch (itemId) {
case R.id.mnuFree:
this.rssUrl = "http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topfreeapplications/limit=%d/xml";
break;
case R.id.mnuPaid:
this.rssUrl = "http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/toppaidapplications/limit=%d/xml";
break;
case R.id.mnuSongs:
this.rssUrl = "http://ax.itunes.apple.com/WebObjects/MZStoreServices.woa/ws/RSS/topsongs/limit=%d/xml";
break;
default:
return super.onOptionsItemSelected(item);
}
processRss(String.format(this.rssUrl, this.feedLimit));
Log.d(TAG, "onOptionsItemSelected: processRss() called");
return true;
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putString(KEY_RSS_URL, this.rssUrl);
outState.putInt(KEY_FEED_LIMIT, this.feedLimit);
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
this.rssUrl = savedInstanceState.getString(KEY_RSS_URL);
this.feedLimit = savedInstanceState.getInt(KEY_FEED_LIMIT);
processRss(String.format(this.rssUrl, this.feedLimit));
Log.d(TAG, "onRestoreInstanceState: processRss() called");
}
private void processRss(String rssUrl) {
StringRequest stringRequest = new StringRequest(Request.Method.GET, rssUrl, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
ParseApplication parseApplication = new ParseApplication();
if (parseApplication.parse(response)) {
ArrayAdapter<FeedEntry> arrayAdapter = new FeedAdapter(
MainActivity.this,
R.layout.list_record,
parseApplication.getApplications(),
VolleySingleton.getInstance(MainActivity.this).getImageLoader());
xmlListView.setAdapter(arrayAdapter);
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e(TAG, "onErrorResponse: from volley : " + error.getMessage());
}
});
VolleySingleton.getInstance(this).addToRequestQueue(stringRequest);
}
}
对于 VolleySingleton，我使用这段代码，getRequestQueue 使用缓存
公开课 VolleySingleton {
private static VolleySingleton mInstance;
private static Context mCtx;
private RequestQueue mRequestQueue;
private ImageLoader mImageLoader;
private VolleySingleton(Context context) {
mCtx = context;
mRequestQueue = getRequestQueue();
mImageLoader = new ImageLoader(mRequestQueue,
new ImageLoader.ImageCache() {
private final LruCache<String, Bitmap>
cache = new LruCache<String, Bitmap>(20);
@Override
public Bitmap getBitmap(String url) {
return cache.get(url);
}
@Override
public void putBitmap(String url, Bitmap bitmap) {
cache.put(url, bitmap);
}
});
}
public static synchronized VolleySingleton getInstance(Context context) {
if (mInstance == null) {
mInstance = new VolleySingleton(context);
}
return mInstance;
}
private RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
File cacheDir = new File(mCtx.getCacheDir(), "VOLLEY_CACHE_DIR");
mRequestQueue = new RequestQueue(
new DiskBasedCache(cacheDir, 512 * 512),
new BasicNetwork(new HurlStack()));
mRequestQueue.start();
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> req) {
getRequestQueue().add(req);
}
public ImageLoader getImageLoader() {
return mImageLoader;
}
}
【问题讨论】：
标签： java android networking android-volley