Question

我是XAML的新手。我编写了以下例程，以一个给定的角度（0到360）旋转图像。我放入一个滑块控件来根据滑块值设置角度。效果很好！但是，在运行程序并单击“旋转”按钮时，For / Next循环从0变为360，图像将仅显示最后一个角度旋转（360）。我确实放入了一个Sleep命令，以防万一我没有抓住以前的更新。任何有关它不会不断更新的帮助将不胜感激。谢谢。

Imports System.Threading.Thread
Imports System.Windows.Media.Imaging.BitmapImage

Class MainWindow

    Private Sub Slider1_ValueChanged(sender As System.Object, e As System.Windows.RoutedPropertyChangedEventArgs(Of System.Double)) Handles Slider1.ValueChanged
' ---- when I adjust manually, this works perfectly
        Dim rotateTransform1 As New RotateTransform
        rotateTransform1.Angle = Slider1.Value
        lblAngle.Content = rotateTransform1.Angle
        Image1.RenderTransform = rotateTransform1
    End Sub

    Private Sub btnSpin_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles btnSpin.Click
    Dim spinAngle as Double
    For SpinAngle 0 to 360
            spinWheel(spinAngle)
            Sleep(50)
        Next spinAngle
    End Sub

    Private Sub spinWheel(ByVal spinAngle)
        Dim rotateTransform1 As New RotateTransform
        rotateTransform1.Angle = SpinAngle 'Slider1.Value
       Image1.RenderTransform = rotateTransform1
        lblAngle.Content = rotateTransform1.Angle
        Image1.InvalidateVisual()

    End Sub

    Public Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
        ' Image1.createOption = BitmapCreateOptions.IgnoreImageCache

    End Sub

End Class

XAML

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="677" Width="910">
    <Grid Background="#FF006903">
        <Grid.RowDefinitions>
            <RowDefinition Height="238*" />
            <RowDefinition Height="178*" />
        </Grid.RowDefinitions>
        <Button Content="SPIN!" Height="23" HorizontalAlignment="Left" Margin="521,101,0,0" Name="btnSpin" VerticalAlignment="Top" Width="75" Grid.Row="1" FontFamily="Tahoma" FontSize="15" FontWeight="ExtraBold" />
        <Image Height="615" Margin="32,7,0,0" Name="Image1" Stretch="None" VerticalAlignment="Top"
               RenderTransformOrigin=" 0.5,0.5"    Source="/rotatePicture;component/Images/purp_wheel_cropped.png"
               Grid.RowSpan="2" HorizontalAlignment="Left" Width="619" />

        <Slider Height="25" HorizontalAlignment="Left" Margin="127,188,0,0" Name="Slider1" VerticalAlignment="Top" Width="350" Maximum="360" Grid.Row="1" />
        <Label Content="Label" Height="28" HorizontalAlignment="Left" Margin="521,175,0,0" Name="lblAngle" VerticalAlignment="Top" Width="75" Grid.Row="1" FontFamily="Tahoma" FontSize="15" FontWeight="ExtraBold" />
        <Image Height="29" HorizontalAlignment="Left" Margin="535,252,0,0" Name="Image2" Stretch="Fill" VerticalAlignment="Top" Width="55" Source="/rotatePicture;component/Images/wheel_pointer.png" />
    </Grid>
</Window>

Answer 1

您的方法存在的问题是，您通过在Click处理程序中重复调用Sleep 阻止UI线程。 WPF为您要做的事情提供了一个非常优雅的机制。它被称为Animation。

为FrameworkElement的旋转设置动画的方法可能如下所示在C＃中（对不起，但我不会说VB）。

private void RotateElement(
    FrameworkElement element, double from, double to, TimeSpan duration)
{
    var transform = element.RenderTransform as RotateTransform;
    if (transform != null)
    {
        var animation = new DoubleAnimation(from, to, duration);
        transform.BeginAnimation(RotateTransform.AngleProperty, animation);
    }
}

请注意RotateTransform必须已包含在RenderTransform的{{1}}属性中。例如，它可以在XAML中分配，如下所示：

FrameworkElement

您可以在Button Click处理程序中调用<Image RenderTransformOrigin="0.5,0.5" ...> <Image.RenderTransform> <RotateTransform/> </Image.RenderTransform> </Image>方法，如下所示：

RotateElement

另请注意，在private void btnSpin_Click(object sender, RoutedEventArgs e) { RotateElement(Image1, 0, 360, TimeSpan.FromMilliseconds(360 * 50)); }中，也无需每次都创建新的Slider1_ValueChanged。

此外，很少有人像RotateTransform那样拨打InvalidateVisual。

Answer 2

克莱门斯的回答很好。不要忘记您可以暂停/恢复动画，但前提是您在代码隐藏中创建动画。如果我没记错的话，如果你在XAML中启动它们就无法控制动画。

WPF映像仅在最后一帧的运行时更新

2 个答案: