嗨,我正在尝试使用
Android 4中引入的HttpResponseCache.该文档清楚地说明如何安装缓存,但是我完全失去了如何缓存从网络下载的图像.更早我正在使用DiskLruCache缓存它们.任何人都会指出一些使用HttpResponseCache的工作代码的例子.
编辑： – 有人可以告诉我我在这里做错了什么：
MainActivity.java
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
final File httpCacheDir = new File(getCacheDir(),"http");
try {
Class.forName("android.net.http.HttpResponseCache")
.getMethod("install",File.class,long.class)
.invoke(null,httpCacheDir,httpCacheSize);
Log.v(TAG,"cache set up");
} catch (Exception httpResponseCacheNotAvailable) {
Log.v(TAG,"android.net.http.HttpResponseCache not available,probably because we're running on a pre-ICS version of Android. Using com.integralblue.httpresponsecache.HttpHttpResponseCache.");
try{
com.integralblue.httpresponsecache.HttpResponseCache.install(httpCacheDir,httpCacheSize);
}catch(Exception e){
Log.v(TAG,"Failed to set up com.integralblue.httpresponsecache.HttpResponseCache");
}
}
TheMainListFrag gf=(TheMainListFrag) getSupportFragmentManager().findFragmentByTag("thelistfrags");
if(gf==null){
gf=TheMainListFrag.newInstance();
FragmentTransaction ft=getSupportFragmentManager().beginTransaction();
ft.replace(R.id.thelefty,gf,"thelistfrags");
ft.commit();
}
}
然后在TheMainListFrag的加载器中,我做下面的：
public ArrayList<HashMap<String,String>> loadInBackground() {
String datafromServer = null;
ArrayList<HashMap<String,String>> al = new ArrayList<HashMap<String,String>>();
try {
String url = "someurl";
HttpURLConnection urlConnection = (HttpURLConnection) new URL(url).openConnection();
urlConnection.setRequestProperty("Accept","application/json");
InputStream is = new BufferedInputStream(urlConnection.getInputStream());
BufferedReader br = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = br.readLine()) != null) {
sb.append(line);
}
datafromServer=sb.toString();
Log.v("fromthread",datafromServer);
// etc
//etc
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (Exception e) {
Log.v("fromthread",e.getClass() + "--" + e.getMessage());
}
return al;
}
当我连接到互联网,它工作正常,在目录http – 上面命名的缓存目录中,我也可以看到文件.但是当我没有连接到互联网时,数据拒绝加载.
当我从网络加载图像时,我看到名为.tmp的缓存文件,据我所知,DiskLruCache被认为是脏的.
请让我知道,如果有任何其他信息,你要我提供
解决方法
从
HttpResponseCache documentation强制缓存响应部分：
Sometimes you’ll want to show resources if they are available
immediately,but not otherwise. This can be used so your application
can show @H_301_24@something while waiting for the latest data to be
downloaded. To restrict a request to locally-cached resources,add the
only-if-cacheddirective:
try {
connection.addRequestProperty("Cache-Control","only-if-cached");
InputStream cached = connection.getInputStream();
// the resource was cached! show it
} catch (FileNotFoundException e) {
// the resource was not cached
}
This technique works even better in situations where a stale response
is better than no response. To permit stale cached responses,use the
max-staledirective with the maximum staleness in seconds:
int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
connection.addRequestProperty("Cache-Control","max-stale=" + maxStale);
