添加文本後UILabel反彈

Question

將文本以編程方式添加到UILabel。隨着更多文本的添加，文本將包裝並增加標籤的高度。

的問題是，當文本換行在一行的末尾，整個標籤會跳起來1線的高度和動畫本身回落到它的正確位置。最終的結果很好，但你如何擺脫奇怪的跳躍動畫。同樣，每當UILabel的高度因另一行換行而增加時，就會發生這種情況。

示例代碼：

var eventCount = 0; 
func someEvent(sender:AnyObject){ 
    eventCount += 1; 
    if(eventCount == 1){ 
     lbl.text = "this" 
    }else if(eventCount == 2){ 
     lbl.text = "this is some" 
    }else if(eventCount == 3){ 
     lbl.text = "this is some sample text" 
    }else if(eventCount == 4){ 
     // this is where text wraps to line 2 
     // the label jumps up 20px or so and 
     // animates back down to it's original position 
     lbl.text = "this is some sample text that causes the label to wrap" 
    } 
} 

自動版式約束

  0 
      | 
    0 - UILabel - 0 

標籤屬性

lines = 0 

Answer 1

我已經設法再現與下面的代碼的問題：

class ViewController: UIViewController { 

    @IBOutlet weak var label: UILabel! 

    @IBAction func buttonPushed(sender: AnyObject) { 
     UIView.animateWithDuration(0.5) { 
      self.someEvent(self) 
      self.view.layoutIfNeeded() 
     } 
    } 

    func someEvent(sender:AnyObject){ 
     self.label.text! += " test" 
    } 
} 

所以，我相信你的someEvent()的動畫塊中調用。

UIView.performWithoutAnimation解決了這個問題。

var eventCount = 0; 
func someEvent(sender:AnyObject){ 
    UIView.performWithoutAnimation { 
     self.eventCount += 1; 
     if(self.eventCount == 1){ 
      self.lbl.text = "this" 
     }else if(self.eventCount == 2){ 
      self.lbl.text = "this is some" 
     }else if(self.eventCount == 3){ 
      self.lbl.text = "this is some sample text" 
     }else if(self.eventCount == 4){ 
      self.lbl.text = "this is some sample text that causes the label to wrap" 
     } 
     self.view.layoutIfNeeded() 
    } 
}