ios - 在自动布局环境中移动 UIView

Question

在我的 View Controller 中，我有两个对象。 TopView 和 CustomScrollView。 我想将 TopView 放在顶部，将 CustomScrollView 放在它们下面，所以我把它放在:

// TOP VIEW LAYOUT

// horizontal

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|    [_topView]|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(_topView, self)]];
// vertical

 [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_topView(89)]" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(_topView, self)]];


// CUSTOMSCROLLVIEW

// horizontal

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[_customScrollVeiw]|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(_customScrollVeiw, self)]];
// vertical

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[_topView]-(0)-[_customScrollVeiw]|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(_customScrollVeiw, _topView,  self)]]; 

并且工作正常。

但现在我想在 CustomScrollView 中滚动时移动顶 View ，所以我创建了这个函数:

- (void) moveOnScroll: (CGPoint) offset contentSize: (CGSize) contentSize
{
float delta = offset.y - self.yPosition;
if (self.yPosition > offset.y) {
    if (labs(self.frame.origin.y) < self.frame.size.height/50 ){
        self.frame = CGRectMake(0, 0, self.frame.size.width, self.frame.size.height);
    }

    else if (self.frame.origin.y - delta < 0 && offset.y < (contentSize.height - self.screenHeight)){
        self.frame = CGRectMake(0, self.frame.origin.y - delta, self.frame.size.width, self.frame.size.height);
    }
    else{
        self.frame = CGRectMake(0, 0, self.frame.size.width, self.frame.size.height);
    }
}
else {
    if (self.frame.origin.y > (- self.frame.size.height  + self.labelHeight) && offset.y > 0){

        if (self.frame.origin.y - delta < (- self.frame.size.height  + self.labelHeight )) {
            self.frame = CGRectMake(0, (- self.frame.size.height  + self.labelHeight ), self.frame.size.width, self.frame.size.height);
        }
        else{
            self.frame = CGRectMake(0, self.frame.origin.y - delta , self.frame.size.width, self.frame.size.height);
        }
    }
}
self.yPosition = offset.y;
}

现在 TopView 在我滚动时隐藏了，但 CustomScrollView 不再紧贴 TopView，它停留在他的位置并且不移动。 (V:[_topView]-(0)-[_customScrollVeiw]|)

如何解决这个问题？

Answer 1

将此约束保存在 View Controller 中的某处

// vertical
NSArray *topViewContstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_topView(89)]" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(_topView, self)]
for (NSLayoutConstraint *constraint in topViewContstraints) {
    if (constraint.firstAttribute == NSLayoutAttributeHeight) {
        _topViewConstraint = constraint;
        break;
    }
}
[self.view addConstraints:topViewContstraints];

然后通过保存的约束更改顶 View 的 y 位置:

_topViewConstraint.constant = yOffset;

其中 yOffset 是您自定义方法中的计算值。

哦，你会想要动画这个变化:

[UIView animateWithDuration:0.3 animations:^{
         [_topView layoutIfNeeded];
}];