如何从'sender'对象访问用户定义的运行时属性？

Question

我在Storyboard场景中有一个UIButton。该按钮配置了User-Defined-RunTime-Attribute'type'（String）。按下按钮调用

-(IBAction)pressedButton:(id)sender

我是否可以从'sender'访问User-Defined-RunTime-Attribute？

Answer 1

是：

-(IBAction)pressedButton:(id)sender
{
    id value = [sender valueForKey:key];
}

---

请注意，您不能使用“用户定义的运行时”属性，除非您将UIButton子类化并将其添加为强属性，例如

@interface UINamedButton : UIButton
@property (strong) NSString *keyName;
@end

如果您设置了“用户定义的运行时”属性，但尚未执行此操作，则不幸的是Xcode会严重崩溃。

然后你可以获得像

这样的价值

-(IBAction)clicked:(UIControl *)sender
    {
    NSString *test = @"???";

    if ( [sender respondsToSelector:@selector(keyName)] )
            test = [sender valueForKey:@"keyName"];

    NSLog(@"the value of keyName is ... %@", test);

    // if you FORGOT TO SET the keyName value in storyboard, that will be NULL
    // if it's NOT a UINamedButton button, you'll get the "???"

    // and for example...
    [self performSegueWithIdentifier:@"idUber" sender:sender];
    // ...the prepareForSegue could then use that value in the button.

    // note that a useful alternative to
    // if ( [sender respondsToSelector:@selector(stringTag)] )
    // is... 
    // if ( [sender respondsToSelector:NSSelectorFromString(@"stringTag")] )
    }