1.首先创建按钮并对按钮设置 contentEdgeInsets 属性
     self.textBtn.contentEdgeInsets = UIEdgeInsetsMake(20, 20, 20, 20);
2.获取按钮和按钮中文字的 frame

    //frame方法
    - (CGSize)sizeWithText:(NSString *)text font:(UIFont *)font maxSize:(CGSize)maxSize{
        NSDictionary *attr = @{NSFontAttributeName : font};
        return [text boundingRectWithSize:maxSize options:NSStringDrawingUsesLineFragmentOrigin attributes:attr context:nil].size;
    }

    //调用frame方法
    CGSize textSize = [self sizeWithText:message.text font:MNTextFont maxSize:CGSizeMake(200, MAXFLOAT)];

    if (message.type == MNMessageTypeOther) {
      _textF =  CGRectMake(CGRectGetMaxX(_iconF) + 10, CGRectGetMaxY(_timeF)+15, textSize.width+40, textSize.height+40);
    }else{
        _textF =  CGRectMake(screenW-10-40-10-textSize.width-40, CGRectGetMaxY(_timeF)+15, textSize.width+40, textSize.height+40);
}

3.拉伸填充
    - (UIImage *)resizableImageWithCapInsets:(NSString *)name{
        UIImage *normal = [UIImage imageNamed:name];
        CGFloat normaiW = normal.size.width * 0.5;
        CGFloat normaiH = normal.size.height *0.5;
        return [normal resizableImageWithCapInsets:UIEdgeInsetsMake(normaiH, normaiW, normaiH, normaiW)];
}        

例子:
if (message.type == MNMessageTypeMe) {
    [self.textBtn setBackgroundImage:[self resizableImageWithCapInsets:@"chat_send_nor"] forState:UIControlStateNormal];
}else{
    [self.textBtn setBackgroundImage:[self resizableImageWithCapInsets:@"chat_recive_nor"] forState:UIControlStateNormal];
}

分类中封装
1.创建分类文件 UIImage+Extension.h/UIImage+Extension.h
2.在UIImage+Extension.h中创建方法
+ (UIImage *)resizableImageWithCapInsets:(NSString *)name;
3.实现该方法
+ (UIImage *)resizableImageWithCapInsets:(NSString *)name{
UIImage *normal = [UIImage imageNamed:name];
CGFloat normaiW = normal.size.width * 0.5;
CGFloat normaiH = normal.size.height *0.5;
return [normal resizableImageWithCapInsets:UIEdgeInsetsMake(normaiH, normaiW, normaiH, normaiW)];
}

例子:

 if (message.type == MNMessageTypeMe) {
    [self.textBtn setBackgroundImage:[UIImage resizableImageWithCapInsets:@"chat_send_nor"] forState:UIControlStateNormal];
}else{
    [self.textBtn setBackgroundImage:[UIImage resizableImageWithCapInsets:@"chat_recive_nor"] forState:UIControlStateNormal];
}