我试图使用HttpResponseCache来缓存网络数据，但当我将安装缓存代码放入OnCreate和OnPause方法时，应用程序崩溃。我使用了HttpResponseCache文档中的代码。并且编译错误如下所示。使用后
@TargetApi（内部版本_CODES.ICE_CREAM_SANDWICH）
为了解决错误，它消失了，我运行了应用程序，但仍然崩溃。当我删除该代码时，它会恢复到正常行为。
protected void onCreate(Bundle savedInstanceState) {
...
try {
File httpCacheDir = new File(context.getCacheDir(), "http");
long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
HttpResponseCache.install(httpCacheDir, httpCacheSize); //error
} catch (IOException e) {
Log.i(TAG, "HTTP response cache installation failed:" + e);
}
}
protected void onStop() {
...
HttpResponseCache cache = HttpResponseCache.getInstalled();//error
if (cache != null) {
cache.flush();//error
}
}}
我是一个初学者，所以如果有人能帮我，我将不胜感激。这是主要活动代码
public class MainActivity extends AppCompatActivity {
private MovieAdapter movieAdapter;
private Context context;
@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// ------ caching data ------------------
try {
File httpCacheDir = new File(context.getCacheDir(), "http");
long httpCacheSize = 2 * 1024 * 1024; // 10 MiB
HttpResponseCache.install(httpCacheDir, httpCacheSize); //error
} catch (IOException e) {
Log.i("caching failed", "HTTP response cache installation failed:" + e);
}
//-----------------------
DataSyncTask dataSyncTask = new DataSyncTask();
dataSyncTask.execute();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
startActivity(new Intent(this, SettingsActivity.class));
return true;
}
return super.onOptionsItemSelected(item);
}
private class DataSyncTask extends AsyncTask<Void, Void, ArrayList<Movie>> {
@Override
protected ArrayList<Movie> doInBackground(Void... params) {
JSONHttpClient jsonHttpClient = new JSONHttpClient(MainActivity.this);
JSONDataParser finalData = new JSONDataParser();
/*
using shared preference to obtain data
*/
SharedPreferences sharedPreferences =
PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
String sortingOrder = sharedPreferences.getString(
getString(R.string.pref_findMovies_key),
getString(R.string.pref_popular_value));
String streamData = jsonHttpClient.getData(sortingOrder);
return finalData.getParsedData(streamData);
}
@Override
protected void onPostExecute(final ArrayList<Movie> movies) {
movieAdapter = new MovieAdapter(getApplicationContext(), movies);
GridView gridView = (GridView) findViewById(R.id.movies_grid);
gridView.setAdapter(movieAdapter);
gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
Movie movie = (Movie) adapterView.getItemAtPosition(i);
Intent intent = new Intent(MainActivity.this, DetailActivity.class);
intent.putExtra("MovieTitle", movie.getTitle());
intent.putExtra("voteAverage", movie.getVoteAverage());
intent.putExtra("ReleaseDate", movie.getReleaseDate());
intent.putExtra("MovieOverview", movie.getOverview());
intent.putExtra("PosterPath", movie.getPosterPath());
startActivity(intent);
}
});
}
}
@Override
protected void onResume() {
DataSyncTask dataSyncTask = new DataSyncTask();
dataSyncTask.execute();
super.onResume();
}
@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
@Override
protected void onStop() {
HttpResponseCache cache = HttpResponseCache.getInstalled();
if (cache != null) {
cache.flush();
}
super.onStop();
}
}
应用程序崩溃后出现在logcat中的
12-19 19:22:58.465 17548-17548/com.example.geekymind.displayjsondatafrominternet W/dalvikvm﹕ VFY: unable to find class referenced in signature (Landroid/view/SearchEvent;)
12-19 19:22:58.465 17548-17548/com.example.geekymind.displayjsondatafrominternet I/dalvikvm﹕ Could not find method android.view.Window$Callback.onSearchRequested, referenced from method android.support.v7.internal.view.WindowCallbackWrapper.onSearchRequested
12-19 19:22:58.465 17548-17548/com.example.geekymind.displayjsondatafrominternet W/dalvikvm﹕ VFY: unable to resolve interface method 14585: Landroid/view/Window$Callback;.onSearchRequested (Landroid/view/SearchEvent;)Z
12-19 19:22:58.465 17548-17548/com.example.geekymind.displayjsondatafrominternet I/dalvikvm﹕ Could not find method android.view.Window$Callback.onWindowStartingActionMode, referenced from method android.support.v7.internal.view.WindowCallbackWrapper.onWindowStartingActionMode
12-19 19:22:58.465 17548-17548/com.example.geekymind.displayjsondatafrominternet W/dalvikvm﹕ VFY: unable to resolve interface method 14589: Landroid/view/Window$Callback;.onWindowStartingActionMode (Landroid/view/ActionMode$Callback;I)Landroid/view/ActionMode;
12-19 19:22:58.505 17548-17548/com.example.geekymind.displayjsondatafrominternet I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getChangingConfigurations, referenced from method android.support.v7.internal.widget.TintTypedArray.getChangingConfigurations
12-19 19:22:58.505 17548-17548/com.example.geekymind.displayjsondatafrominternet W/dalvikvm﹕ VFY: unable to resolve virtual method 451: Landroid/content/res/TypedArray;.getChangingConfigurations ()I
12-19 19:22:58.515 17548-17548/com.example.geekymind.displayjsondatafrominternet I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getType, referenced from method android.support.v7.internal.widget.TintTypedArray.getType
12-19 19:22:58.515 17548-17548/com.example.geekymind.displayjsondatafrominternet W/dalvikvm﹕ VFY: unable to resolve virtual method 473: Landroid/content/res/TypedArray;.getType (I)I
12-19 19:22:58.585 17548-17548/com.example.geekymind.displayjsondatafrominternet W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x415ffc80)
根据HttpResponseCache文档：
通过以下方式启用对应用程序的所有HTTP请求的缓存在应用程序启动时安装缓存。
所以你应该使用如下：
MyApplication.java：
public class MyApplication extends Application {
private final Context mContext = this;
public void onCreate() {
super.onCreate();
// Install the cache
try {
File httpCacheDir = new File(mContext.getCacheDir(), "http");
long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
HttpResponseCache.install(httpCacheDir, httpCacheSize);
} catch (IOException e) {
Log.i("CacheHttpUrlConnection", "HTTP response cache installation failed:" + e);
}
// Register for activity lifecycle callbacks,
// specifically interested in activity stop callbacks.
registerActivityLifecycleCallbacks(
new MyApplicationActivityLifeCycleCallbacks());
}
// method to flush cache contents to the filesystem
public void flushCache() {
HttpResponseCache cache = HttpResponseCache.getInstalled();
if (cache != null) {
cache.flush();
}
}
private class MyApplicationActivityLifeCycleCallbacks implements ActivityLifecycleCallbacks {
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
}
@Override
public void onActivityStarted(Activity activity) {
}
@Override
public void onActivityResumed(Activity activity) {
}
@Override
public void onActivityPaused(Activity activity) {
}
public void onActivityStopped(Activity activity) {
flushCache();
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
}
@Override
public void onActivityDestroyed(Activity activity) {
}
}
}
MainActivity.java:
AsyncTask类的doInBackground内部：
...
URL url = new URL(address);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
urlConnection.addRequestProperty("Cache-Control", "max-stale=" + maxStale);
// Checks cache
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
cache = HttpResponseCache.getInstalled();
if (cache != null) {
cacheInfo = "Request count: "
+ cache.getRequestCount() + ", hit count "
+ cache.getHitCount() + ", network count "
+ cache.getNetworkCount() + " size = "
+ cache.size() + " <-----------------";
Log.i(LOG_TAG, cacheInfo);
}
}
// Gets stream
Log.i(LOG_TAG, "RespCode: " + urlConnection.getResponseCode());
if (urlConnection.getResponseCode() < HttpURLConnection.HTTP_BAD_REQUEST) {
inputStream = urlConnection.getInputStream();
} else {
inputStream = urlConnection.getErrorStream();
}
// Parses stream to string
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String temp, response = "";
while ((temp = bufferedReader.readLine()) != null) {
response += temp;
}
...
AndroidManifest.xml:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.cachehttpurlconnection" >
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme"
android:name="com.example.cachehttpurlconnection.MyApplication" >
<activity android:name=".MainActivity" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>