Question

我实现了UINavigationController，根视图控制器隐藏或显示内容，具体取决于用户在导航堆栈中做出的选择。所有隐藏/显示选项都在根视图控制器文件中的viewWillAppear函数中实现。现在，当根视图控制器首次出现时，没有问题。但是，当我更深入，更改一些内容然后按几次后退按钮并进入我的根视图控制器时，ViewWillAppear函数不会立即调用，但是会在延迟之后调用。

结果如何？我之前留下的视图首先被加载，然后逐渐一些按钮开始消失。但是，我希望这些按钮在视图显示之前消失。为此，我需要在视图实际显示之前执行viewWillAppear，就像应用首次出现一样。

我意识到有些开发人员遇到viewWillAppear根本没有被调用的问题;但是，在这种情况下，这不是问题：）

- (void)viewWillAppear:(BOOL)animated{

[super viewWillAppear:animated];

AWSCognitoCredentialsProvider *credentialsProvider = [[AWSCognitoCredentialsProvider alloc]
                                                      initWithRegionType:AWSRegionUSEast1
                                                      identityPoolId:@"###-####-###"];

AWSServiceConfiguration *configuration = [[AWSServiceConfiguration alloc] initWithRegion:AWSRegionUSEast1 credentialsProvider:credentialsProvider];

[AWSServiceManager defaultServiceManager].defaultServiceConfiguration = configuration;

AWSDynamoDBObjectMapper *dynamoDBObjectMapper = [AWSDynamoDBObjectMapper defaultDynamoDBObjectMapper];
AWSDynamoDBQueryExpression *queryExpression = [AWSDynamoDBQueryExpression new];

if ([FBSDKAccessToken currentAccessToken]) {
    queryExpression.indexName = @"FBID-index";
    queryExpression.hashKeyAttribute = @"FBID";
    queryExpression.hashKeyValues = [FBSDKAccessToken currentAccessToken].userID;

}
else{
    queryExpression.hashKeyAttribute = @"ID";
    queryExpression.hashKeyValues = credentialsProvider.identityId;
}

dispatch_semaphore_t sema = dispatch_semaphore_create(0);
[[dynamoDBObjectMapper query:[User class]
                  expression:queryExpression]
 continueWithBlock:^id(AWSTask *task) {

     if (task.error) {
         NSLog(@"The request failed. Error: [%@]", task.error);
     }
     if (task.exception) {
         NSLog(@"The request failed. Exception: [%@]", task.exception);
     }
     if (task.result) {

         AWSDynamoDBPaginatedOutput *paginatedOutput = task.result;

         //there should really only be one entry with the specified CognitoID
         User *user = [paginatedOutput.items objectAtIndex:0];

         if(user.Login==true||user.Login==1){
             if ([FBSDKAccessToken currentAccessToken]) {
                 login.hidden = YES;

             }
             else{
                 FBlogin.hidden = YES;
                 [login setTitle: @"Log Out" forState: UIControlStateNormal];
             }


         }
         else{

             FBlogin.hidden = YES;
         }

         dispatch_semaphore_signal(sema);
     }
     return nil;
 }];

while (dispatch_semaphore_wait(sema, DISPATCH_TIME_NOW)) { [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate dateWithTimeIntervalSinceNow:1]]; }
}

ViewWillAppear在延迟后调用

0 个答案: