objective-c - 无法从存储中删除 NSURLCredentials

Question

从我的应用程序中删除帐户时，我正在尝试从存储中删除凭据。这是我正在使用的代码：

NSDictionary *dict = [[NSURLCredentialStorage sharedCredentialStorage] allCredentials];
NSDictionary *dictCopy = [dict copy];
for(NSURLProtectionSpace *key in [dictCopy keyEnumerator])
{
    NSDictionary *value = [dict objectForKey:key];
    NSURLCredential *cred = [value objectForKey:accountLogin];
    if(cred)
        [[NSURLCredentialStorage sharedCredentialStorage] removeCredential:cred forProtectionSpace:key];
}
NSLog(@"%@",[[NSURLCredentialStorage sharedCredentialStorage] allCredentials]);

为所有正确的键和值调用删除部分，但在方法完成后，所有凭据仍然完好无损。这怎么可能？

我也尝试过设置新凭据，但似乎它们也没有被识别