UILabel默认不带内边距，调整内边距步骤：

1.制定一个空白区：UIEdgeInsets。

2. 重写drawTextInRect，传入空白区。

3.重新计算扩大label的frame（空白区占用frame的空间，导致显示不全）。

代码：

#import "SFLabel.h"
#import <UIKit/UIKit.h>
@interface SFLabel ()
// 用来决定上下左右内边距，也可以提供一个借口供外部修改，在这里就先固定写死
@property (assign, nonatomic) UIEdgeInsets edgeInsets;
@end

@implementation SFLabel


//下面三个方法用来初始化edgeInsets
- (instancetype)initWithFrame:(CGRect)frame
{
    if(self = [super initWithFrame:frame])
    {
        self.edgeInsets = UIEdgeInsetsMake(25, 0, 25, 0);
    }
    return self;
}

- (instancetype)initWithCoder:(NSCoder *)aDecoder
{
    if (self = [super initWithCoder:aDecoder]) {
        self.edgeInsets = UIEdgeInsetsMake(25, 0, 25, 0);
    }
    return self;
}

- (void)awakeFromNib
{
   [super awakeFromNib];
    self.edgeInsets = UIEdgeInsetsMake(25, 0, 25, 0);
}

// 修改绘制文字的区域，edgeInsets增加bounds
-(CGRect)textRectForBounds:(CGRect)bounds limitedToNumberOfLines:(NSInteger)numberOfLines
{

    /*
    调用父类该方法
    注意传入的UIEdgeInsetsInsetRect(bounds, self.edgeInsets),bounds是真正的绘图区域
    */
    CGRect rect = [super textRectForBounds:UIEdgeInsetsInsetRect(bounds,
     self.edgeInsets) limitedToNumberOfLines:numberOfLines];
    //根据edgeInsets，修改绘制文字的bounds
    rect.origin.x -= self.edgeInsets.left;
    rect.origin.y -= self.edgeInsets.top;
    rect.size.width += self.edgeInsets.left + self.edgeInsets.right;
    rect.size.height += self.edgeInsets.top + self.edgeInsets.bottom;
    return rect;
}

//绘制文字
- (void)drawTextInRect:(CGRect)rect
{
    //令绘制区域为原始区域，增加的内边距区域不绘制
    [super drawTextInRect:UIEdgeInsetsInsetRect(rect, self.edgeInsets)];
}
@end