按钮常见的访问方法

当前图片:
[button imageForState:UIControlStateNormal].size;
button.currentImage.size;

背景图片：
[button backgroundImageForState:UIControlStateNormal];
button.currentBackgroundImage;

当前标题:
[button titleForState:UIControlStateNormal];
button.currentTitle;

标题颜色:
[button titleColorForState:UIControlStateNormal];
button.currentTitleColor;

设置按钮的内边距

整个内容的内边距：
@property(nonatomic) UIEdgeInsets contentEdgeInsets UI_APPEARANCE_SELECTOR;
标题的内边距：
@property(nonatomic) UIEdgeInsets titleEdgeInsets;
图片的内边距：
@property(nonatomic) UIEdgeInsets imageEdgeInsets;

viewWithTag:内部的大致实现思路

@implementation UIView
- (UIView *)viewWithTag:(NSInteger)tag
{
    if (self.tag == tag) return self;

    for (UIView *subview in self.subviews) {
        return [subview viewWithTag:tag];
    }
}
@end