延遲UILabel中的文本之間的淡入淡出

Question

我想動畫UILabel的文本，以便它顯示一個文本幾秒鐘，然後淡入默認文本。

我目前使用下面的代碼：

-(void)tapOnBalance:(id)sender{ 
     [UIView animateWithDuration:1.0 delay:0.0 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{ 
     cell.amountLabel.text = @"Hola!"; 
     } completion:nil]; 

     // Pause the function - act as a 'delay' 
     [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:3]]; 

     [UIView animateWithDuration:1.0 delay:0.0 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{ 
     cell.amountLabel.text = @"Hallo!"; 
     } completion:nil]; 

} 

這工作，但[NSRunLoop currentRunLoop]被暫停整個應用程序，3秒阻止一切。

如何擺脫主線程上的塊並仍然得到相同的結果？

Answer 1

一個簡單的淡入淡出（非交叉淡入淡出）可以是這樣的：

// change a label's text after some delay by fading 
// out, changing the text, then fading back in 
- (void)fadeLabel:(UILabel *)label toText:(NSString *)toText completion:(void (^)(BOOL))completion { 
    [UIView animateWithDuration:0.2 delay:0.0 options:UIViewAnimationOptionCurveEaseInOut animations:^{ 
     label.alpha = 0.0; 
    } completion:^(BOOL finished) { 
     label.text = toText; 
     [UIView animateWithDuration:0.2 delay:0.0 options:UIViewAnimationOptionCurveEaseIn animations:^{ 
      label.alpha = 1.0; 
     } completion:completion]; 
    }]; 
} 

// simpler signature that can be done on a perform 
- (void)changeLabelText:(NSString *)toText { 
    [self fadeLabel:self.myLabel toText:toText completion:nil]; 
} 

// set the label to something, then change it with a fade, then change it back 
self.myLabel.text = @"text"; 
[self performSelector:@selector(changeLabelText:) withObject:@"hola!" afterDelay:4]; 
[self performSelector:@selector(changeLabelText:) withObject:@"text" afterDelay:8]; 

你也嵌套調用完成塊（並添加延遲PARAM）做不執行類似的東西。爲了進行交叉淡入淡出，應用一種類似的技巧，使用兩個標籤（具有相同的框架），其中一個的alpha值爲零，另一個的alpha值爲1。