拖动view

#import "ViewController.h"
#import <Masonry/Masonry.h>

@interface ViewController ()

@property (strong, nonatomic) UIView *containerView;
@property (strong, nonatomic) UILabel *logLabel;
@property (nonatomic, strong) UILabel *tipLabel;
@property (nonatomic, strong) MASConstraint *leftConstraint;
@property (nonatomic, strong) MASConstraint *topConstraint;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self.view addSubview:self.containerView];
    [self.view addSubview:self.logLabel];
    [_containerView addSubview:self.tipLabel];
    [self p_addMasonry];
    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panWithGesture:)];
    [_containerView addGestureRecognizer:pan];
}

- (void)p_addMasonry {
    [_tipLabel mas_makeConstraints:^(MASConstraintMaker *make) {
        // 设置边界条件约束，保证内容可见，优先级1000
        make.left.mas_greaterThanOrEqualTo(_containerView.mas_left);
        make.right.mas_lessThanOrEqualTo(_containerView.mas_right);
        make.top.mas_greaterThanOrEqualTo(_containerView.mas_top);
        make.bottom.mas_lessThanOrEqualTo(_containerView.mas_bottom);
        
        _leftConstraint = make.centerX.equalTo(_containerView.mas_left).mas_offset(50).priorityHigh(); // 优先级要比边界条件低
        _topConstraint = make.centerY.equalTo(_containerView.mas_top).mas_offset(50).priorityHigh(); // 优先级要比边界条件低
        make.width.mas_equalTo(CGRectGetWidth(_tipLabel.frame) + 8);
        make.height.mas_equalTo(CGRectGetHeight(_tipLabel.frame) + 4);
    }];
}

- (void)panWithGesture:(UIPanGestureRecognizer *)pan {
    CGPoint touchPoint = [pan locationInView:_containerView];
    _logLabel.text = NSStringFromCGPoint(touchPoint);
    
    _leftConstraint.offset = touchPoint.x;
    _topConstraint.offset = touchPoint.y;
}

- (UIView *)containerView {
    if (!_containerView) {
        _containerView = [[UIView alloc] init];
        _containerView.layer.masksToBounds = YES;
        _containerView.layer.borderWidth = 1.0f;
        _containerView.layer.borderColor = [UIColor redColor].CGColor;
        _containerView.frame = CGRectMake(15, 100, [UIScreen mainScreen].bounds.size.width - 30, [UIScreen mainScreen].bounds.size.width - 30);
    }
    return _containerView;
}

- (UILabel *)tipLabel {
    if (!_tipLabel) {
        _tipLabel = [[UILabel alloc] init];
        _tipLabel.textColor = [UIColor whiteColor];
        _tipLabel.font = [UIFont systemFontOfSize:20];
        _tipLabel.numberOfLines = 2;
        _tipLabel.textAlignment = NSTextAlignmentCenter;
        _tipLabel.backgroundColor = [UIColor colorWithRed:0.39 green:0.39 blue:0.39 alpha:1];
        _tipLabel.layer.borderColor = [UIColor blackColor].CGColor;
        _tipLabel.layer.borderWidth = 1.0f;
        _tipLabel.layer.masksToBounds = YES;
        _tipLabel.layer.cornerRadius = 2.0f;
        _tipLabel.text = @"tutuge.me\niOS";
        [_tipLabel sizeToFit];
    }
    return _tipLabel;
}

- (UILabel *)logLabel {
    if (!_logLabel) {
        _logLabel = [[UILabel alloc] init];
        _logLabel.textColor = [UIColor whiteColor];
        _logLabel.font = [UIFont systemFontOfSize:20];
        _logLabel.numberOfLines = 2;
        _logLabel.textAlignment = NSTextAlignmentCenter;
        _logLabel.backgroundColor = [UIColor colorWithRed:0.39 green:0.39 blue:0.39 alpha:1];
        _logLabel.layer.borderColor = [UIColor blackColor].CGColor;
        _logLabel.layer.borderWidth = 1.0f;
        _logLabel.layer.masksToBounds = YES;
        _logLabel.layer.cornerRadius = 2.0f;
        _logLabel.frame = CGRectMake(0, CGRectGetMaxY(_containerView.frame) + 10, [UIScreen mainScreen].bounds.size.width, 40);
    }
    return _logLabel;
}

@end