设置约束

gistfile1.m

-(void)p_updateConstraints{
    [self.contentView removeConstraints:self.contentView.constraints];
    NSDictionary *views=@{@"contentLabel":self.contentLabel};
    NSMutableArray *constraints=[NSMutableArray array];
    //设置水平约束
    [constraints addObjectsFromArray:[NSLayoutConstraint
                                      constraintsWithVisualFormat:@"H:|-5-[contentLabel]-5-|"
                                      options:0
                                      metrics:nil
                                      views:views]];
    
    //设置垂直约束
    [constraints addObjectsFromArray:[NSLayoutConstraint
                                      constraintsWithVisualFormat:@"V:|-5-[contentLabel]-5-|"
                                      options:0
                                      metrics:nil
                                      views:views]];
    
    [self.contentView addConstraints:constraints];
}