iOS开发UILabel顶端左对齐

这样写文字会显示在中间

    UILabel *content = [[UILabel alloc]init];
    [self.contentImageView addSubview:content];
    content.numberOfLines = 0;
    content.text = @"测试测试测试测试测试";
    [content mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.equalTo(self.contentImageView).offset(28);
        make.top.equalTo(self.contentImageView).offset(20);
        make.bottom.equalTo(self.contentImageView).offset(-20);
        make.right.equalTo(self.contentImageView).offset(-28);
    }];

顶端左对齐

    TopLeftLabel *content = [[TopLeftLabel alloc]init];
    [self.contentImageView addSubview:content];
    content.numberOfLines = 0;
    content.text = @"测试测试测试测试测试";
    [content mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.equalTo(self.contentImageView).offset(28);
        make.top.equalTo(self.contentImageView).offset(20);
        make.bottom.equalTo(self.contentImageView).offset(-20);
        make.right.equalTo(self.contentImageView).offset(-28);
    }];

#import "TopLeftLabel.h"

@implementation TopLeftLabel

- (id)initWithFrame:(CGRect)frame {
    return [super initWithFrame:frame];
}
- (CGRect)textRectForBounds:(CGRect)bounds limitedToNumberOfLines:(NSInteger)numberOfLines {
    CGRect textRect = [super textRectForBounds:bounds limitedToNumberOfLines:numberOfLines];
    textRect.origin.y = bounds.origin.y;
    return textRect;
}
-(void)drawTextInRect:(CGRect)requestedRect {
    CGRect actualRect = [self textRectForBounds:requestedRect limitedToNumberOfLines:self.numberOfLines];
    [super drawTextInRect:actualRect];
}

@end