我们可以退出一个函数（不是从应用程序）或者甚至使用跳转到特定行吗？

Question

我正在寻找如何在函数中间退出或跳转到函数的末尾。

我有一个函数，在这个函数中有几个验证需要完成。对于每次验证，我都使用 alertView。

        if spacing_CenterToCenter < 2 {

        let alertView = UIAlertController(title: "Stem Rebars Spacing C/C",
            message: "Spacing of Rebars C/C < 2 inches, you must increase the Diameter of Stem Rebars", preferredStyle: .Alert)
        let OKAction = UIAlertAction(title: "Change now", style: .Default, handler: {
            (action: UIAlertAction!) -> Void in
            self.dismissViewControllerAnimated(true, completion: nil)
        })
        alertView.addAction(OKAction)        
        self.presentViewController(alertView, animated: false, completion: nil)
    }

这里有额外的代码

再次验证

    if spacing_HorizontalStemRebars < 2 {
        let alertView = UIAlertController(title: "Temp/Shrink Rebars Spacing C/C",
        message: "Spacing of Rebars C/C < 2 inches, you must increase the Diameter of Temperature and Shrinkage Rebars", preferredStyle: .Alert)

        let OKAction = UIAlertAction(title: "Change now", style: .Default, handler: {
            (action: UIAlertAction!) -> Void in
            self.dismissViewControllerAnimated(true, completion: nil)               
        })
        alertView.addAction(OKAction)
        self.presentViewController(alertView, animated: false, completion: nil)
    }

此处添加代码

函数结束

}

如果我运行应用程序并且我有 spacing_CenterToCenter < 2 和 spacing_HorizontalStemRebars < 2，我将收到以下错误：

2015-12-15 20:08:02.684 Retaining-Wall[3845:162311] Warning: Attempt to present on while a presentation is in progress!

如果我只有 spacing_CenterToCenter < 2 或只有 spacing_HorizontalStemRebars < 2，应用程序将运行没有错误。所以，我想使用命令退出或跳转到函数的末尾，这将在每个验证中。这样函数只会做一次验证，如果失败它会跳到函数的末尾。

有什么建议吗？

Answer 1

您可以使用 return，如果您没有 return 类型，它会退出函数。
或者你可以使用 guard

guard spacing_CenterToCenter < 2 else{
  // Show alert
  return
}

Answer 2

好吧，如果您正在寻找任何 "one" 条件足以显示错误的情况，只需使用 else if 而不是多个 if's

func checking(){
if spacing_CenterToCenter < 2 {

    let alertView = UIAlertController(title: "Stem Rebars Spacing C/C",
        message: "Spacing of Rebars C/C < 2 inches, you must increase the Diameter of Stem Rebars", preferredStyle: .Alert)
    let OKAction = UIAlertAction(title: "Change now", style: .Default, handler: {
        (action: UIAlertAction!) -> Void in
        self.dismissViewControllerAnimated(true, completion: nil)
    })
    alertView.addAction(OKAction)        
    self.presentViewController(alertView, animated: false, completion: nil)
}
else if spacing_HorizontalStemRebars < 2 {
    let alertView = UIAlertController(title: "Temp/Shrink Rebars Spacing C/C",
    message: "Spacing of Rebars C/C < 2 inches, you must increase the Diameter of Temperature and Shrinkage Rebars", preferredStyle: .Alert)

    let OKAction = UIAlertAction(title: "Change now", style: .Default, handler: {
        (action: UIAlertAction!) -> Void in
        self.dismissViewControllerAnimated(true, completion: nil)               
    })
    alertView.addAction(OKAction)
    self.presentViewController(alertView, animated: false, completion: nil)
}

}

如果你不看这样的东西，你可以让你的检查函数 return 成为一个 bool 并在 main 函数中跟踪你的 bool return。

在检查函数中：

func checking() -> Bool {
if spacing_CenterToCenter < 2 {

    let alertView = UIAlertController(title: "Stem Rebars Spacing C/C",
        message: "Spacing of Rebars C/C < 2 inches, you must increase the Diameter of Stem Rebars", preferredStyle: .Alert)
    let OKAction = UIAlertAction(title: "Change now", style: .Default, handler: {
        (action: UIAlertAction!) -> Void in
        self.dismissViewControllerAnimated(true, completion: nil)
    })
    alertView.addAction(OKAction)        
    self.presentViewController(alertView, animated: false, completion: nil)
//return a false if this get triggered after showing the error
return false;
}

if spacing_HorizontalStemRebars < 2 {
    let alertView = UIAlertController(title: "Temp/Shrink Rebars Spacing C/C",
    message: "Spacing of Rebars C/C < 2 inches, you must increase the Diameter of Temperature and Shrinkage Rebars", preferredStyle: .Alert)

    let OKAction = UIAlertAction(title: "Change now", style: .Default, handler: {
        (action: UIAlertAction!) -> Void in
        self.dismissViewControllerAnimated(true, completion: nil)               
    })
    alertView.addAction(OKAction)
    self.presentViewController(alertView, animated: false, completion: nil)
//return a false if this get triggered after showing the error
return false;
}
//if it has reached this return statement means nothing went wrong and return a true.
return true;

}

现在在主函数中：

var checkReturns = checking();
if (!checkReturns) {
    //your "false" condition processing
}
//your "true" coondition processing

我们可以退出一个函数（不是从应用程序）或者甚至使用跳转到特定行吗？

Can we exit from a function (Not from application) or even use a jump to certain line?

exit

swift