我正在使用azure移动服务创建一个Android应用程序。我有一个始终运行的服务（使用startForeground（））并监视一些用户活动。该服务有时需要以这种方式查询存储在azure云中的azure数据库调用API：
mClient.invokeApi("APIname", null, "GET", parameters);
//mClient is the MobileServiceClient instance
一开始，用户使用LoginActivity登录，一切正常。经过一段时间（通常是1小时）后，客户端的令牌已过期，我收到了这样的例外：
IDX10223: Lifetime validation failed. The token is expired.
经过一些搜索，我找到了解决方案来刷新令牌： https://github.com/Microsoft/azure-docs/blob/master/includes/mobile-android-authenticate-app-refresh-token.md
如果活动处于活动状态，则代码可以正常运行并成功刷新令牌（如果已过期）。但如果活动被破坏，它就无法运作。所以我决定将ApplicationContext传递给客户端，这样：
mClient.setContext(activity.getApplicationContext());
但现在我收到一个ClassCastException，因为客户端试图将上下文转换为Activity。以下是例外的有趣内容：
java.lang.ClassCastException: android.app.Application cannot be cast to android.app.Activity
at com.microsoft.windowsazure.mobileservices.authentication.LoginManager.showLoginUI(LoginManager.java:349)
at com.microsoft.windowsazure.mobileservices.authentication.LoginManager.authenticate(LoginManager.java:161)
at com.microsoft.windowsazure.mobileservices.MobileServiceClient.login(MobileServiceClient.java:371)
at com.microsoft.windowsazure.mobileservices.MobileServiceClient.login(MobileServiceClient.java:356)
at com.microsoft.windowsazure.mobileservices.MobileServiceClient.login(MobileServiceClient.java:309)
那么如何在没有活动的情况下从服务刷新令牌？或者还有另一种方法可以让客户端始终进行身份验证吗？
修改
我尝试在这里粘贴一些代码，希望能让我更清楚地使用身份验证令牌。我有一个用于管理身份验证的LoginManager。这里有一些有意义的代码：
public boolean loadUserTokenCache(Context context)
{
init(context); //update context
SharedPreferences prefs = context.getSharedPreferences(SHARED_PREF_FILE, Context.MODE_PRIVATE);
String userId = prefs.getString(USERID_PREF, null);
if (userId == null)
return false;
String token = prefs.getString(LOGIN_TOKEN_PREF, null);
if (token == null)
return false;
MobileServiceUser user = new MobileServiceUser(userId);
user.setAuthenticationToken(token);
mClient.setCurrentUser(user);
return true;
}
过滤器是：
private class RefreshTokenCacheFilter implements ServiceFilter {
AtomicBoolean mAtomicAuthenticatingFlag = new AtomicBoolean();
//--------------------http://stackoverflow.com/questions/7860384/android-how-to-runonuithread-in-other-class
private final Handler handler;
public RefreshTokenCacheFilter(Context context){
handler = new Handler(context.getMainLooper());
}
private void runOnUiThread(Runnable r) {
handler.post(r);
}
//--------------------
@Override
public ListenableFuture<ServiceFilterResponse> handleRequest(
final ServiceFilterRequest request,
final NextServiceFilterCallback nextServiceFilterCallback
)
{
// In this example, if authentication is already in progress we block the request
// until authentication is complete to avoid unnecessary authentications as
// a result of HTTP status code 401.
// If authentication was detected, add the token to the request.
waitAndUpdateRequestToken(request);
Log.d(Constants.TAG, logClassIdentifier+"REFRESH_TOKEN_CACHE_FILTER is Sending the request down the filter chain for 401 responses");
Log.d(Constants.TAG, logClassIdentifier+mClient.getContext().toString());
// Send the request down the filter chain
// retrying up to 5 times on 401 response codes.
ListenableFuture<ServiceFilterResponse> future = null;
ServiceFilterResponse response = null;
int responseCode = 401;
for (int i = 0; (i < 5 ) && (responseCode == 401); i++)
{
future = nextServiceFilterCallback.onNext(request);
try {
response = future.get();
responseCode = response.getStatus().code;
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
if (e.getCause().getClass() == MobileServiceException.class)
{
MobileServiceException mEx = (MobileServiceException) e.getCause();
responseCode = mEx.getResponse().getStatus().code;
if (responseCode == 401)
{
// Two simultaneous requests from independent threads could get HTTP status 401.
// Protecting against that right here so multiple authentication requests are
// not setup to run on the UI thread.
// We only want to authenticate once. Requests should just wait and retry
// with the new token.
if (mAtomicAuthenticatingFlag.compareAndSet(false, true))
{
// Authenticate on UI thread
runOnUiThread(new Runnable() {
@Override
public void run() {
// Force a token refresh during authentication.
SharedPreferences pref = context.getSharedPreferences(Constants.SHARED_PREF_FILE, Context.MODE_PRIVATE);
MobileServiceAuthenticationProvider provider = Utilities.getProviderFromName(pref.getString(Constants.LAST_PROVIDER_PREF, null));
authenticate(context, provider, true);
}
});
}
// Wait for authentication to complete then update the token in the request.
waitAndUpdateRequestToken(request);
mAtomicAuthenticatingFlag.set(false);
}
}
}
}
return future;
}
}
身份验证方法（为了正确显示对话框和主要活动，我修改了一些小东西，但它的工作方式应该与Microsoft的原始代码相同）：
/**
* Returns true if mClient is not null;
* A standard sign-in requires the client to contact both the identity
* provider and the back-end Azure service every time the app starts.
* This method is inefficient, and you can have usage-related issues if
* many customers try to start your app simultaneously. A better approach is
* to cache the authorization token returned by the Azure service, and try
* to use this first before using a provider-based sign-in.
* This authenticate method uses a token cache.
*
* Authenticates with the desired login provider. Also caches the token.
*
* If a local token cache is detected, the token cache is used instead of an actual
* login unless bRefresh is set to true forcing a refresh.
*
* @param bRefreshCache
* Indicates whether to force a token refresh.
*/
public boolean authenticate(final Context context, MobileServiceAuthenticationProvider provider, final boolean bRefreshCache) {
if (mClient== null)
return false;
final ProgressDialog pd = null;//Utilities.createAndShowProgressDialog(context, "Logging in", "Log in");
bAuthenticating = true;
// First try to load a token cache if one exists.
if (!bRefreshCache && loadUserTokenCache(context)) {
Log.d(Constants.TAG, logClassIdentifier+"User cached token loaded successfully");
// Other threads may be blocked waiting to be notified when
// authentication is complete.
synchronized(mAuthenticationLock)
{
bAuthenticating = false;
mAuthenticationLock.notifyAll();
}
QueryManager.getUser(context, mClient, mClient.getCurrentUser().getUserId(), pd);
return true;
}else{
Log.d(Constants.TAG, logClassIdentifier+"No cached token found or bRefreshCache");
}
// If we failed to load a token cache, login and create a token cache
init(context);//update context for client
ListenableFuture<MobileServiceUser> mLogin = mClient.login(provider);
Futures.addCallback(mLogin, new FutureCallback<MobileServiceUser>() {
@Override
public void onFailure(Throwable exc) {
String msg = exc.getMessage();
if ( msg.equals("User Canceled"))
return;
if ( pd!= null && pd.isShowing())
pd.dismiss();
createAndShowDialog(context, msg, "Error");
synchronized(mAuthenticationLock)
{
bAuthenticating = false;
mAuthenticationLock.notifyAll();
}
}
@Override
public void onSuccess(MobileServiceUser user) {
cacheUserToken(context, mClient.getCurrentUser());
if(!bRefreshCache)//otherwise main activity is launched even from other activity (like shop activity)
QueryManager.getUser(context, mClient, mClient.getCurrentUser().getUserId(), pd);//loads user's info and shows MainActivity
else if ( pd!= null && pd.isShowing())
pd.dismiss();
synchronized(mAuthenticationLock)
{
bAuthenticating = false;
mAuthenticationLock.notifyAll();
}
ClientUtility.UserId = mClient.getCurrentUser().getUserId();
}
});
return true;
}
答案 0 :(得分：1)
我认为API应该有一个方法来刷新令牌而不显示活动（据我所知，只需要插入凭据;但令牌刷新不需要凭据）。我正在考虑的另一个解决方案是切换到另一个云服务提供商，放弃Microsoft Azure :(
答案 1 :(得分：0)
错误java.lang.ClassCastException: android.app.Application cannot be cast to android.app.Activity是由方法MobileServiceClient.setContext引起的，需要Activity的上下文，例如activity.this，但来自activity.getApplicationContext()的上下文是整个Android应用程序。这是不正确的用法。
Cache authentication tokens on the client部分显示了符合您需求的官方解决方案，请参阅该解决方案以尝试解决您的问题。