UIEdgeInsets
UIEdgeInsets 设置边距
UIEdgeInsets UIEdgeInsetsMake (
CGFloat top,
CGFloat left,
CGFloat bottom,
CGFloat right
);
按钮button中自带有一个label，通过设置label的边距可以自定义label在按钮中的位置：
[button setTitleEdgeInsets:UIEdgeInsetsMake(0,0,0，0)];
设置按钮自带的label显示在按钮的右方（右对齐）
[button setContentHorizontalAlignment:UIControlContentHorizontalAlignmentRight];