iOS 用keypath设置一些属性

1.UIButton title 距左边显

button.contentHorizontalAlignment = UIControlContentHorizontalAlignmentLeft;

　　

　　

2.UITextField placeholder 颜色

方法一：

textField.placeholder = @"this is placeholder";  
[textFieldsetValue:[UIColor redColor]forKeyPath:@"_placeholderLabel.textColor"];  
[textFieldsetValue:[UIFontboldSystemFontOfSize:16]forKeyPath:@"_placeholderLabel.font"]; 

　　

方法二：（iOS 6 之后）

NSMutableAttributedString *placeholder = [[NSMutableAttributedString alloc]initWithString:@"this is placeholder"];

[placeholderaddAttribute:NSForegroundColorAttributeName
                  value:[UIColor redColor]
                  range:NSMakeRange(0, placeholder.length)];

[placeholderaddAttribute:NSFontAttributeName
                  value:[UIFontboldSystemFontOfSize:14]
                  range:NSMakeRange(0, placeholder.length)];


textField.attributedPlaceholder = placeholder;

3.隐藏 tabBar 顶部的分割线

[self.tabBar setValue:@(YES) forKeyPath:@"_hidesShadow"];