VisualStateManager 无法在 UserControl 上启动动画

我尝试在 Windows Phone 7 Silverlight 项目中使用 VisualStateManager 在 UserControl 上启动动画，但它不起作用。 GoToState 只是不断返回 false。

该代码包含一个 VisualState 行为，当数据上下文上的 State 属性发生更改时，该行为将运行 GoToState，这在单击 UI 中的按钮时会发生：

我究竟做错了什么？

XAML:

    <Grid>
        <UserControl x:Name="_testSubject" l:VisualStates.CurrentState="{Binding State}" />
        <Button VerticalAlignment="Bottom" Content="Change state" Click="Button_Click" />
        <VisualStateManager.VisualStateGroups>
            <VisualStateGroup>
                <VisualState x:Name="State2">
                    <Storyboard>
                        <ColorAnimation From="Red" To="Green" Duration="0:0:10" Storyboard.TargetProperty="Background" Storyboard.TargetName="_testSubject" />
                    </Storyboard>
                </VisualState>
            </VisualStateGroup>
        </VisualStateManager.VisualStateGroups>
    </Grid>

C#:

public class Test : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    void OnPropertyChanged(string name) { if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(name)); }
    string _state;
    public string State { get { return _state; } set { _state = value; OnPropertyChanged("State"); } }
}

public static class VisualStates
{
    public static readonly DependencyProperty CurrentStateProperty =
        DependencyProperty.RegisterAttached("CurrentState", typeof(String), typeof(VisualStates), new PropertyMetadata(TransitionToState));

    public static string GetCurrentState(DependencyObject obj)
    {
        return (string)obj.GetValue(CurrentStateProperty);
    }

    public static void SetCurrentState(DependencyObject obj, string value)
    {
        obj.SetValue(CurrentStateProperty, value);
    }

    private static void TransitionToState(object sender, DependencyPropertyChangedEventArgs args)
    {
        Control c = sender as Control;
        if (c != null)
        {
            bool b = VisualStateManager.GoToState(c, (string)args.NewValue, false);
        }
        else
        {
            throw new ArgumentException("CurrentState is only supported on the Control type");
        }
    }

public partial class MainPage : PhoneApplicationPage
{
    public MainPage() { InitializeComponent(); }

    private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
    {
        _testSubject.DataContext = new Test();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        ((Test)_testSubject.DataContext).State = "State2";
    }
}

只是一个疯狂的猜测，但它可能是在错误的线程中执行的吗？您可能希望使用调度程序在正确的 (UI) 线程上执行它。

GoToState 在 Button_Click 函数中工作吗？

private void Button_Click(object sender, RoutedEventArgs e)
{
    bool b = VisualStateManager.GoToState(this, "State2", false);
}

当您执行代码时是否会调用 TransitionToState？

这将排除任何其他问题。

UPDATE

以下内容对我有用。我在设置背景时遇到了一些问题。首先，这对 UserControl 没有任何影响，其次不可能使用颜色动画更改背景，这就是我更改不透明度的原因。

主页.xaml

<Grid x:Name="ContentPanel"
      Grid.Row="1"
      Margin="12,0,12,0">
    <Grid.RowDefinitions>
        <RowDefinition />
        <RowDefinition />
        <RowDefinition Height="*" />
    </Grid.RowDefinitions>
    <l:TestControl x:Name="_testSubject"
                   Grid.Row="0"
                   l:VisualStates.CurrentState="{Binding State}" />

    <UserControl x:Name="_test2Subject"
                 Height="100"
                 Grid.Row="1"
                 l:VisualStates.CurrentState="{Binding State}">
        <Grid x:Name="aLayoutRoot"
              Background="Wheat">
            <VisualStateManager.VisualStateGroups>
                <VisualStateGroup x:Name="CommonStates">
                    <VisualState x:Name="State2">
                        <Storyboard>
                            <DoubleAnimation Storyboard.TargetName="aLayoutRoot"
                                             Storyboard.TargetProperty="Opacity"
                                             From="1"
                                             To="0"
                                             Duration="0:0:2"
                                             AutoReverse="True" />
                        </Storyboard>
                    </VisualState>
                </VisualStateGroup>
            </VisualStateManager.VisualStateGroups>
        </Grid>
    </UserControl>

    <Button Click="Button_Click"
            Content="Click"
            Grid.Row="2" />


</Grid>

测试控件.xaml

<UserControl x:Class="PhoneApp1.TestControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    d:DesignHeight="480" d:DesignWidth="480">

    <Grid x:Name="LayoutRoot" Background="Wheat">
        <VisualStateManager.VisualStateGroups>
            <VisualStateGroup x:Name="CommonStates">
                <VisualState x:Name="State2">
                    <Storyboard>
                        <DoubleAnimation Storyboard.TargetName="LayoutRoot"
                                         Storyboard.TargetProperty="Opacity"
                                         From="1"
                                         To="0"
                                         Duration="0:0:2"
                                         AutoReverse="True" />
                    </Storyboard>
                </VisualState>
            </VisualStateGroup>
        </VisualStateManager.VisualStateGroups>
    </Grid>
</UserControl>

Test.cs / TransitionToState 方法

private static void TransitionToState(object sender, DependencyPropertyChangedEventArgs args)
{
    UserControl c = sender as UserControl;
    if (c != null && args.NewValue != null)
    {
        bool b = VisualStateManager.GoToState(c, (string)args.NewValue, true);
        var a = b;
    }
}

主页.cs

public MainPage()
{
    InitializeComponent();

    _testSubject.DataContext = new Test();
    _test2Subject.DataContext = new Test();

}

private void Button_Click(object sender, RoutedEventArgs e)
{
    ((Test)_testSubject.DataContext).State = "State2";
    ((Test)_test2Subject.DataContext).State = "State2"; 
}

我还建议使用 ControlTemplates 来分配 VisualStates，而不是直接在控件上定义它们。这将为您提供更大的灵活性、更好的维护等。

希望这可以帮助。