我试图在我的 ViewController 中有一个可拖动的 UIView，最终这个 UIView 将变成一个可点击的按钮，但现在，当它被拖动到屏幕上时，我无法更新这个 View 的约束。代码如下。

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.anotherView = [[UIView alloc]init];
    UIPanGestureRecognizer *panRecognizer = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(dragging:)];
    [self.anotherView addGestureRecognizer:panRecognizer];
    [self.anotherView setBackgroundColor: [UIColor blueColor]];
    self.anotherView.translatesAutoresizingMaskIntoConstraints = NO;

    [self.view addSubview: self.anotherView];
    [self.view bringSubviewToFront:self.anotherView];

    NSDictionary *views = @{@"subview" : self.anotherView, @"superview" : self.view};

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.anotherView
                                                          attribute:NSLayoutAttributeLeft
                                                          relatedBy:NSLayoutRelationLessThanOrEqual
                                                             toItem:self.view
                                                          attribute:NSLayoutAttributeLeft
                                                         multiplier:1.0
                                                           constant:0]];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.anotherView
                                                          attribute:NSLayoutAttributeCenterY
                                                          relatedBy:NSLayoutRelationLessThanOrEqual
                                                             toItem:self.view
                                                          attribute:NSLayoutAttributeCenterY
                                                         multiplier:1.0
                                                           constant:0]];


    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.anotherView
                                                          attribute:NSLayoutAttributeWidth
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:Nil
                                                          attribute:NSLayoutAttributeWidth
                                                         multiplier:1.0
                                                           constant:20]];

    [self.view addConstraints:[NSLayoutConstraint
                               constraintsWithVisualFormat:@"V:[subview(40)]"
                               options:0
                               metrics:nil
                               views:views]];
        // add horizontal constraints

    /*[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[subview(==20)]|" options:0 metrics:nil views:views]];

     // set the height of the offscreen subview to be the same as its superview

     [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[subview(==40)]" options:0 metrics:nil views:views]];

     // set the location of the subview to be just off screen below the current view

     NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:self.anotherView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationLessThanOrEqual toItem:self.view attribute:NSLayoutAttributeHeight multiplier:1.0 constant:self.view.bounds.size.height];
     [self.view addConstraint:constraint];*/
        //[self.anotherView pinEdges:JRTViewPinLeftEdge toSameEdgesOfView:self.view];


        // Do any additional setup after loading the view, typically from a nib.
    self.navigationItem.leftBarButtonItem = self.editButtonItem;

    UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(insertNewObject:)];
    self.navigationItem.rightBarButtonItem = addButton;
    self.detailViewController = (DetailViewController *)[[self.splitViewController.viewControllers lastObject] topViewController];
}

上面的代码是我在 ViewController 中设置 UIView 的方式。预计尺寸为 20x45。拖动代码如下:

-(void)dragging:(UIPanGestureRecognizer *)gesture
{
    if(gesture.state == UIGestureRecognizerStateBegan)
        {
            //NSLog(@"Received a pan gesture");
        self.panCoord = [gesture locationInView:gesture.view];
        [self.tableView setScrollEnabled:NO];

        }
    CGPoint newCoord = [gesture locationInView:gesture.view];
    float dX = newCoord.x-self.panCoord.x;
    float dY = newCoord.y-self.panCoord.y;
    CGFloat newXPoint;
    CGFloat newYPoint;

    gesture.view.frame = CGRectMake(gesture.view.frame.origin.x+dX, gesture.view.frame.origin.y+dY, gesture.view.frame.size.width, gesture.view.frame.size.height);
    if (gesture.state == UIGestureRecognizerStateEnded) {
        newYPoint = gesture.view.frame.origin.y+dY;
        if (gesture.view.frame.origin.x+dX<(self.view.frame.size.width/2)) {
            newXPoint = 0;
        }
        else {
            newXPoint = self.view.frame.size.width - gesture.view.frame.size.width;
//The below is just an attempt to remove and re-add constraints so the view will stick to the right side of the screen. It is not working :( 
            [self.view removeConstraint:[NSLayoutConstraint constraintWithItem:self.anotherView
                                                                  attribute:NSLayoutAttributeLeft
                                                                  relatedBy:NSLayoutRelationLessThanOrEqual
                                                                     toItem:self.view
                                                                  attribute:NSLayoutAttributeLeft
                                                                 multiplier:1.0
                                                                   constant:0]];

            [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.anotherView
                                                                  attribute:NSLayoutAttributeRight
                                                                  relatedBy:NSLayoutRelationLessThanOrEqual
                                                                     toItem:self.view
                                                                  attribute:NSLayoutAttributeRight
                                                                 multiplier:1.0
                                                                   constant:0]];


        }


            //        self.draggedViewCoordinate = gesture.view.frame.origin;

        [UIView beginAnimations:nil context:nil];
        [UIView setAnimationDuration:0.70];
        [UIView setAnimationDelay:0.0];
        [UIView setAnimationCurve:UIViewAnimationCurveEaseOut];
        [self.anotherView layoutIfNeeded];
        [UIView commitAnimations];
        [self.tableView setScrollEnabled:YES];
    }

}

我不知道如何更新约束以使 View 保持在新的拖动位置。有人可以帮忙吗？

最佳答案

接受的答案不正确。 UI 添加/删除约束是非常昂贵的操作。 适当的解决方案将改变

self.yCoordinate.constant

和

self.xCoordinate.constant

基于 dX 和 dY 的属性。

关于ios - 动态/可拖动 UIView 的自动布局，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19398662/