在自动布局环境中移动Uiview

Question

在我的视图控制器中，我有两个对象。TopView和CustomScrollview。我想将topiveie放在顶部，并在他们的下方定位customscrollview，所以我说：

// 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)]]; 

效果很好。

，但是现在我想在CustomScrollview滚动时移动顶视图，因此我创建此功能：

- (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，当我滚动时，TopView正在隐藏，但是CustomScrollview不再拥抱TopView，它一直保持在他的位置，并且不会移动。（v：[_ topview] - （0） - [_ CustomScrollveiw] |）

如何解决此问题？

Answer 1

在视图控制器中的某个地方保存此约束

// 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视图的位置：

_topViewConstraint.constant = yOffset;

yoffset在您的自定义方法中计算的值。

哦，您将需要动画此更改：

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