Question

我正在使用UWP开发Microsoft Store App，并且正在使用XAML和C＃。我想用不透明动画随机更改背景图像。

我的代码在下面。

此函数以Task.Run(InitializeWorks);

执行

    private async void InitializeWorks()
    {
        await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, async () =>
        {
            BackgroundImage.Opacity = 0;
            try
            {
                while (true)
                {
                    var backgroundImageFolder = await Windows.ApplicationModel.Package.Current.InstalledLocation.GetFolderAsync(@"Assets\BackgroundImages");
                    var backgroundImageFiles = await backgroundImageFolder.GetFilesAsync();
                    BackgroundImage.Source = new BitmapImage(new Uri(backgroundImageFiles[new Random().Next(0, backgroundImageFiles.Count)].Path));
                    for (double i = BackgroundImage.Opacity; i <= 0.1; i += 0.001)
                    {
                        BackgroundImage.Opacity = i;
                        await Task.Delay(10);
                    }
                    await Task.Delay(5000);
                    for (double i = BackgroundImage.Opacity; i >= 0; i -= 0.001)
                    {
                        BackgroundImage.Opacity = i;
                        await Task.Delay(10);
                    }
                }

            }
            catch (Exception e)
            {
                //
            }

        });

    }

此代码的性能如何？给您带来不便这个异步任务？会发生任何错误吗？
如何使用XAML制作变化的动画？

Answer 1

您不能在XAML中调用GetFilesAsync或while，但我建议您用DispatcherTimer替换Tick循环，该循环定期更改背景。

{{1}}事件将在UI线程上引发，这意味着可以安全地在事件处理程序中访问UI元素。异步方法不会阻塞。

Answer 2

您可以在XAML中设置以下动画：

<Page.Resources>
<Storyboard x:Name="MyStoryboard">
            <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="BackgroundImage">
                <EasingDoubleKeyFrame KeyTime="0" Value="0"/>
                <EasingDoubleKeyFrame KeyTime="0:0:3" Value="0.1"/>
                <EasingDoubleKeyFrame KeyTime="0:0:6" Value="0"/>
            </DoubleAnimationUsingKeyFrames>
        </Storyboard>
</Page.Resources>

隐藏代码：

您可以使用 StoryBoard.Begin 开始不透明度动画，并且该动画具有 Completed 事件。您可以订阅该动画来收听是否动画完成。动画完成后，您可以调用 InitializeWorks（）方法再次更改BackgroundImage。这种书写方式将替换您的 While 方法。

private async void InitializeWorks()
        {
            await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, async () =>
            {
                BackgroundImage.Opacity = 0;
                try
                {
                   
                    var backgroundImageFolder = await Windows.ApplicationModel.Package.Current.InstalledLocation.GetFolderAsync(@"Assets\BackgroundImages");
                    var backgroundImageFiles = await backgroundImageFolder.GetFilesAsync();
                    BackgroundImage.Source = new BitmapImage(new Uri(backgroundImageFiles[new Random().Next(0, backgroundImageFiles.Count)].Path));
                    MyStoryboard.Begin();
                    MyStoryboard.Completed += MyStoryboard_Completed;
                }
                catch (Exception e)
                {
                    //
                }

            });

        }

private void MyStoryboard_Completed(object sender, object e)
        {
            InitializeWorks();
        }

Answer 3

我通过@faywang @ mm8找到了解决方案

带有Storyboard的XML动画；

    <Storyboard x:Name="BackgroundImageStoryboardIncrease">
        <DoubleAnimation
            Storyboard.TargetName="BackgroundImage"
            Storyboard.TargetProperty="Opacity"
            From="0"
            To="0.15"
            Duration="0:0:2" />
    </Storyboard>
    <Storyboard x:Name="BackgroundImageStoryboardDecrease">
        <DoubleAnimation
            Storyboard.TargetName="BackgroundImage"
            Storyboard.TargetProperty="Opacity"
            From="0.15"
            To="0"
            Duration="0:0:2" />
    </Storyboard>

C＃更改事件并停留10秒钟：

    private async void InitializeFrontWorks()
    {
        // Animations
        DispatcherTimer dispatcherTimer = new DispatcherTimer
        {
            Interval = TimeSpan.FromSeconds(10)
        };
        var backgroundImageFolder = await Windows.ApplicationModel.Package.Current.InstalledLocation.GetFolderAsync(@"Assets\BackgroundImages");
        var backgroundImageFiles = await backgroundImageFolder.GetFilesAsync();
        AnimationBackgroundImage(backgroundImageFiles);
        dispatcherTimer.Tick += delegate
        {
            AnimationBackgroundImage(backgroundImageFiles);
        };
        dispatcherTimer.Start();
    }
    private void AnimationBackgroundImage(IReadOnlyList<StorageFile> backgroundImageFiles)
    {
        BackgroundImageStoryboardDecrease.Begin();
        BackgroundImageStoryboardDecrease.Completed += delegate
        {
            BackgroundImage.Source = new BitmapImage(new Uri(backgroundImageFiles[new Random().Next(0, backgroundImageFiles.Count)].Path));
            BackgroundImageStoryboardIncrease.Begin();
        };
    }

如何使动画改变背景图像？

3 个答案: