爲什麼我應該在動畫中使用CATransaction？

Question

我發現這個代碼片段：

[self setValue:direction forKey:@"currentDirection"]; 

CAKeyframeAnimation * animation = [CAKeyframeAnimation animationWithKeyPath:@"position"]; 
animation.path = path; 
animation.duration = grids * gridWidth/[self speed]; 
animation.fillMode = kCAFillModeForwards; 
animation.removedOnCompletion = NO; 
animation.delegate = self; 
animation.calculationMode = kCAAnimationLinear; 
[self addAnimation:animation forKey:@"movement"]; 
self.position = destination; 

[CATransaction begin]; 
[CATransaction setValue:[NSNumber numberWithFloat:_turn_duration] 
              forKey:kCATransactionAnimationDuration]; 
eyes.position = eyeDestination; 
pupils.position = pupilDestination; 
[CATransaction commit]; 

CGPathRelease(path); 

這裏有什麼用CATransaction點？

Answer 1

將事務中兩個隱式動畫的持續時間設置爲與以上關鍵幀動畫持續時間不同的值。交易中的動畫將運行超過_turn_duration秒，而關鍵幀動畫將運行超過grids * gridWidth/[self speed]秒。