如何获得当前高度为 0 的 WPF UI 元素的所需高度? [英] How to get desired height of WPF UI element with current height of 0?

问题描述

我的最终目标是动画化两个用户控件之间的大小变化.我试图实现这一目标的方式产生了一个主要问题.

My ultimate goal is to animate the change in size between two UserControls. The way that I have attempted to achieve this has produced one major problem.

我从一个包含一些基本文本和图标显示的 DataTemplate、一个高度设置为 0 的编辑"用户控件和一个编辑按钮开始.编辑 UserControl 位于 Height="Auto" 的 GridRow 中，因此它也以 0 的高度开始.该按钮具有由按钮单击触发的 DoubleAnimation，它将 UserControl 的高度从 0 设置为 300.这一切都有效正好.这是一个简化的代码示例.

I start with a DataTemplate that contains some basic text and icon display, an 'edit' UserControl with a height set to 0 and an edit button. The edit UserControl is in a GridRow with Height="Auto", so it also starts out with a height of 0. The button has a DoubleAnimation triggered by the button click that animates the height of the UserControl from 0 to 300. This all works just fine. Here is a simplified code example.

<DataTemplate x:Key="UserTemplate" DataType="{x:Type dataTypes:User}">
...
<controls:UserView Grid.Row="1" Grid.ColumnSpan="5" x:Name="EditRow" 
    DataContext="{Binding}" Height="0" />
<controls:UserEditor Grid.Row="2" Grid.ColumnSpan="5" x:Name="EditRow" 
    DataContext="{Binding}" Height="0" />
<Button Grid.Row="0" Grid.Column="4" Name="Edit" Style="{StaticResource ButtonStyle}" 
    ToolTip="Edit user" Click="Button_Click">
    <Image Source="/SolutionName;component/Images/Edit.png" Stretch="None" />
    <Button.Triggers>
        <EventTrigger RoutedEvent="Button.Click">
            <BeginStoryboard>
                <Storyboard>
                    <DoubleAnimation Name="EditRowHeightAnimation" 
    Storyboard.TargetName="EditRow" Storyboard.TargetProperty="Height" From="0" 
    To="300" Duration="00:00:0.5" />
                </Storyboard>
            </BeginStoryboard>
        </EventTrigger>
    </Button.Triggers>
</Button>
...
</DataTemplate>

问题是编辑 UserControl 不是 300 像素高，我不知道它在设计时的高度.我尝试了以下方法，但它不起作用.

The problem is that the edit UserControl is not 300 pixels high and I won't know what height it will be at design time. I tried the following, but it doesn't work.

<DoubleAnimation Name="EditRowHeightAnimation" Storyboard.TargetName="EditRow"
    Storyboard.TargetProperty="Height" From="0" To="{Binding DesiredSize.Height, 
    ElementName=EditRow}" Duration="00:00:0.5" />

我还尝试从后面的代码对编辑 UserControl 调用 Measure() 和 UpdateLayout().我注释掉了按钮单击触发器和 xaml 动画，并从后面的代码中添加了一个......现在这种工作有效，但我总是得到相同的(错误的)DesiredSize.也就是说，UserControl 高度会被动画化，但只是高度错误.这是按钮单击处理程序代码.

I have also tried calling Measure() and UpdateLayout() on the edit UserControl from code behind. I commented out the button click trigger and xaml animation and added one from code behind instead... now this kind of worked, but I always got the same (wrong) DesiredSize. That is, the UserControl height would get animated, but just to the wrong height. Here is the button click handler code.

private void Button_Click(object sender, RoutedEventArgs e)
{
    User currentUser = (User)CollectionViewSource.GetDefaultView(Users).CurrentItem;
    ListBoxItem listBoxItem = (ListBoxItem)
        (UsersListBox.ItemContainerGenerator.ContainerFromItem(currentUser));
    DataTemplate itemDataTemplate = FindResource("UserTemplate") as DataTemplate;
    ContentPresenter contentPresenter = listBoxItem.GetInternal<ContentPresenter>();
    if (itemDataTemplate != null && contentPresenter != null)
    {
        UserEditor userEditor = (UserEditor)itemDataTemplate.FindName("EditRow", 
            contentPresenter);
        userEditor.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
        userEditor.UpdateLayout();
        userEditor.BeginAnimation(HeightProperty, new DoubleAnimation(0, 
            userEditor.DesiredSize.Height, new Duration(new TimeSpan(0, 0, 1)), 
            FillBehavior.HoldEnd), HandoffBehavior.Compose);
    }
}

所以我的问题是，如果 UserControl 的容器对它没有大小限制，当它的当前高度为 0 时，我如何获得 UserControl 的大小?

So my question is how can I get the size that a UserControl would be if its container placed no size restriction upon it, when its current height is 0?

如果有更好的方法来实现我的最终目标，我也很高兴.非常感谢.

I'd also be happy to hear if there is a better way to achieve my ultimate goal. Many thanks in advance.

推荐答案

你可以用 ClipToBound="True" 把你想要大小的内容放到一个Canvas中.然后，您可以操纵 Canvas 的大小，而 Canvas 内的内容大小将始终是其所需的完整大小.

You can put the content you want the size of into a Canvas with ClipToBound="True". Then you can manipulate the size of the Canvas and yet the size of the content inside the Canvas will always be its full desired size.

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