问题描述
当控件变为可见时，如何使控件淡入/淡出。
How would I make a control fade in/out when it becomes Visible.
以下是我失败的尝试：
<Window x:Class="WadFileTester.Form1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Name="MyWindow" Title="WAD File SI Checker" Height="386" Width="563" WindowStyle="SingleBorderWindow" DragEnter="Window_DragEnter" DragLeave="Window_DragLeave" DragOver="Window_DragOver" Drop="Window_Drop" AllowDrop="True">
<Window.Resources>
<Style TargetType="ListView" x:Key="animatedList">
<Style.Triggers>
<DataTrigger Binding="{Binding Visibility}" Value="Visible">
<DataTrigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
Storyboard.TargetProperty="Opacity"
From="0.0" To="1.0" Duration="0:0:5"
/>
</Storyboard>
</BeginStoryboard>
</DataTrigger.EnterActions>
<DataTrigger.ExitActions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
Storyboard.TargetProperty="Opacity"
From="1.0" To="0.0" Duration="0:0:5"
/>
</Storyboard>
</BeginStoryboard>
</DataTrigger.ExitActions>
</DataTrigger>
</Style.Triggers>
</Style>
</Window.Resources>
<Grid>
<ListView Name="listView1" Style="{StaticResource animatedList}" TabIndex="1" Margin="12,41,12,12" Visibility="Hidden">
</ListView>
</Grid>
</Window>
推荐答案
我不知道如何制作两个动画（在纯XAML中淡入和淡出）。但是简单的淡出可以相对简单地实现。用触发器替换DataTriggers，并删除ExitAction，因为它们在淡出场景中没有意义。这就是您将拥有的：
I don't know how to do both animations (fade in and fade out) in pure XAML. But simple fade out can be achieved relatively simple. Replace DataTriggers with Triggers, and remove ExitActions since they makes no sense in Fade out scenario. This is what you will have:
<Style TargetType="FrameworkElement" x:Key="animatedList">
<Setter Property="Visibility" Value="Hidden"/>
<Style.Triggers>
<Trigger Property="Visibility" Value="Visible">
<Trigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation Storyboard.TargetProperty="Opacity"
From="0.0" To="1.0" Duration="0:0:0.2"/>
</Storyboard>
</BeginStoryboard>
</Trigger.EnterActions>
</Trigger>
</Style.Triggers>
</Style>
但是，不要放弃。如果您想同时支持这两种动画，我可以建议在XAML后面进行一些小的编码。在完成技巧之后，我们将通过在XAML中添加一行代码来获得所需的内容：
But hey, don't give up. If you want to support both animations I can suggest small coding behind the XAML. After we do a trick, we will get what you want by adding one line of code in XAML:
<Button Content="Fading button"
x:Name="btn"
loc:VisibilityAnimation.IsActive="True"/>
每次更改btn时，可见性按钮都会变为隐藏/折叠按钮。每次我们更改Visibility时，按钮都会淡入。此技巧将与任何FrameworkElement（包括ListView :)）一起使用。
Every time we change btn.Visibility from Visible to Hidden/Collapsed button will fade out. And every time we change Visibility back the button will fade in. This trick will work with any FrameworkElement (including ListView :) ).
这是VisibilityAnimation.IsActive附加属性的代码：
Here is the code of VisibilityAnimation.IsActive attached property:
public class VisibilityAnimation : DependencyObject
{
private const int DURATION_MS = 200;
private static readonly Hashtable _hookedElements = new Hashtable();
public static readonly DependencyProperty IsActiveProperty =
DependencyProperty.RegisterAttached("IsActive",
typeof(bool),
typeof(VisibilityAnimation),
new FrameworkPropertyMetadata(false, new PropertyChangedCallback(OnIsActivePropertyChanged)));
public static bool GetIsActive(UIElement element)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
return (bool)element.GetValue(IsActiveProperty);
}
public static void SetIsActive(UIElement element, bool value)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
element.SetValue(IsActiveProperty, value);
}
static VisibilityAnimation()
{
UIElement.VisibilityProperty.AddOwner(typeof(FrameworkElement),
new FrameworkPropertyMetadata(Visibility.Visible, new PropertyChangedCallback(VisibilityChanged), CoerceVisibility));
}
private static void VisibilityChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
// So what? Ignore.
}
private static void OnIsActivePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var fe = d as FrameworkElement;
if (fe == null)
{
return;
}
if (GetIsActive(fe))
{
HookVisibilityChanges(fe);
}
else
{
UnHookVisibilityChanges(fe);
}
}
private static void UnHookVisibilityChanges(FrameworkElement fe)
{
if (_hookedElements.Contains(fe))
{
_hookedElements.Remove(fe);
}
}
private static void HookVisibilityChanges(FrameworkElement fe)
{
_hookedElements.Add(fe, false);
}
private static object CoerceVisibility(DependencyObject d, object baseValue)
{
var fe = d as FrameworkElement;
if (fe == null)
{
return baseValue;
}
if (CheckAndUpdateAnimationStartedFlag(fe))
{
return baseValue;
}
// If we get here, it means we have to start fade in or fade out
// animation. In any case return value of this method will be
// Visibility.Visible.
var visibility = (Visibility)baseValue;
var da = new DoubleAnimation
{
Duration = new Duration(TimeSpan.FromMilliseconds(DURATION_MS))
};
da.Completed += (o, e) =>
{
// This will trigger value coercion again
// but CheckAndUpdateAnimationStartedFlag() function will reture true
// this time, and animation will not be triggered.
fe.Visibility = visibility;
// NB: Small problem here. This may and probably will brake
// binding to visibility property.
};
if (visibility == Visibility.Collapsed || visibility == Visibility.Hidden)
{
da.From = 1.0;
da.To = 0.0;
}
else
{
da.From = 0.0;
da.To = 1.0;
}
fe.BeginAnimation(UIElement.OpacityProperty, da);
return Visibility.Visible;
}
private static bool CheckAndUpdateAnimationStartedFlag(FrameworkElement fe)
{
var hookedElement = _hookedElements.Contains(fe);
if (!hookedElement)
{
return true; // don't need to animate unhooked elements.
}
var animationStarted = (bool) _hookedElements[fe];
_hookedElements[fe] = !animationStarted;
return animationStarted;
}
}
这里最重要的是CoerceVisibility（）方法。如您所见，在淡入淡出动画完成之前，我们不允许更改此属性。
The most important thing here is CoerceVisibility() method. As you can see we do not allow changing this property until fading animation is completed.
此代码既不是线程安全的，也不是没有错误的。它的唯一目的是显示方向:)。因此，随时可以改善，编辑并获得声誉;）。
This code is neither thread safe nor bug free. Its only intention is to show the direction :). So feel free to improve, edit and get reputation ;).
这篇关于WPF淡入淡出动画的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！