[UWP]做个调皮的BusyIndicator

1. 前言

最近突然想要个BusyIndicator。做过WPF开发的程序员对BusyIndicator应该不陌生，Extended WPF Toolkit 提供了BusyIndicator的开源实现，Silverlight Toolkit也有一个，这次想要把这个控件移植到UWP中。

2. 先说点正经的

2.1 BusyIndicator的功能

BusyIndicator的功能很简单，就是提示正在执行操作并遮挡不能被修改的内容。通常它派生自ContentControl并提供public bool IsBusy{ get; set; }属性，当设置IsBusy=True时将Content.IsEnabled设置成False，并显示Overlay、BusyContent和一个ProgressBar。在Silverlight中，它的UI如下：

2.2 移植

Extended WPF Toolkit和Silverlight Toolkit中的BusyIndicator实现基本一致，由于Silverlight和各个XAML平台的兼容性都比较好，我选择了Silverlight Toolkit中的BusyIndicator用于移植。事实证明这是个正确的选择，只改动了几行代码就完美移植成功了。

2.3 改进

既然UWP有ProgressRing，我就不想用ProgressBar来展示Busy的状态。另外，虽然BusyIndicator的ControlTemplate已经够精简了，为了方便将来修改我再进一步简化了XAML，结果如下：

<ContentControl x:Name="content"
                Content="{TemplateBinding Content}"
                ContentTemplate="{TemplateBinding ContentTemplate}"
                ContentTransitions="{TemplateBinding ContentTransitions}"
                HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" />
<Rectangle x:Name="overlay"
           Style="{TemplateBinding OverlayStyle}" />
<ContentPresenter x:Name="busycontent">
    <Grid HorizontalAlignment="Center"
          VerticalAlignment="Center">
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <ProgressRing x:Name="ProgressRing"
                      IsActive="True"
                      Style="{TemplateBinding ProgressRingStyle}" />

        <ContentPresenter Content="{TemplateBinding BusyContent}"
                          ContentTemplate="{TemplateBinding BusyContentTemplate}"
                          Grid.Row="1"
                          FontSize="15"
                          HorizontalAlignment="Center"
                          Foreground="{ThemeResource SystemControlHighlightAccentBrush}" />
    </Grid>
</ContentPresenter>

和Silverlight/WPF不同的是，需要在ContentControl上绑定ContentTransitions属性。

UWP可以使用VisualState.Setters代替VisualState.Storyboard，这简化了大量XAML，为什么微软早十年没想到这个做法。

Silverlight的BusyIndicator：

<VisualStateManager.VisualStateGroups>
    <VisualStateGroup x:Name="VisibilityStates">
        <VisualState x:Name="Hidden">
            <Storyboard>
                <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.001" Storyboard.TargetName="busycontent" Storyboard.TargetProperty="(UIElement.Visibility)">
                    <DiscreteObjectKeyFrame KeyTime="00:00:00">
                        <DiscreteObjectKeyFrame.Value>
                            <Visibility>Collapsed</Visibility>
                        </DiscreteObjectKeyFrame.Value>
                    </DiscreteObjectKeyFrame>
                </ObjectAnimationUsingKeyFrames>
                <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.001" Storyboard.TargetName="overlay" Storyboard.TargetProperty="(UIElement.Visibility)">
                    <DiscreteObjectKeyFrame KeyTime="00:00:00">
                        <DiscreteObjectKeyFrame.Value>
                            <Visibility>Collapsed</Visibility>
                        </DiscreteObjectKeyFrame.Value>
                    </DiscreteObjectKeyFrame>
                </ObjectAnimationUsingKeyFrames>
            </Storyboard>
        </VisualState>
        <VisualState x:Name="Visible">
            <Storyboard>
                <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.001" Storyboard.TargetName="busycontent" Storyboard.TargetProperty="(UIElement.Visibility)">
                    <DiscreteObjectKeyFrame KeyTime="00:00:00">
                        <DiscreteObjectKeyFrame.Value>
                            <Visibility>Visible</Visibility>
                        </DiscreteObjectKeyFrame.Value>
                    </DiscreteObjectKeyFrame>
                </ObjectAnimationUsingKeyFrames>
                <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.001" Storyboard.TargetName="overlay" Storyboard.TargetProperty="(UIElement.Visibility)">
                    <DiscreteObjectKeyFrame KeyTime="00:00:00">
                        <DiscreteObjectKeyFrame.Value>
                            <Visibility>Visible</Visibility>
                        </DiscreteObjectKeyFrame.Value>
                    </DiscreteObjectKeyFrame>
                </ObjectAnimationUsingKeyFrames>
            </Storyboard>
        </VisualState>
    </VisualStateGroup>
    <VisualStateGroup x:Name="BusyStatusStates">
        <VisualState x:Name="Idle">
            <Storyboard>
                <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.001" Storyboard.TargetName="content" Storyboard.TargetProperty="(Control.IsEnabled)">
                    <DiscreteObjectKeyFrame KeyTime="00:00:00">
                        <DiscreteObjectKeyFrame.Value>
                            <sys:Boolean>True</sys:Boolean>
                        </DiscreteObjectKeyFrame.Value>
                    </DiscreteObjectKeyFrame>
                </ObjectAnimationUsingKeyFrames>
            </Storyboard>
        </VisualState>
        <VisualState x:Name="Busy">
            <Storyboard>
                <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.001" Storyboard.TargetName="content" Storyboard.TargetProperty="(Control.IsEnabled)">
                    <DiscreteObjectKeyFrame KeyTime="00:00:00">
                        <DiscreteObjectKeyFrame.Value>
                            <sys:Boolean>False</sys:Boolean>
                        </DiscreteObjectKeyFrame.Value>
                    </DiscreteObjectKeyFrame>
                </ObjectAnimationUsingKeyFrames>
            </Storyboard>
        </VisualState>
    </VisualStateGroup>
</VisualStateManager.VisualStateGroups>

UWP的BusyIndicator

<VisualStateManager.VisualStateGroups>
    <VisualStateGroup x:Name="VisibilityStates">
        <VisualState x:Name="Hidden">
            <VisualState.Setters>
                <Setter Target="overlay.(UIElement.Visibility)"
                        Value="Collapsed" />
                <Setter Target="busycontent.(UIElement.Visibility)"
                        Value="Collapsed" />
            </VisualState.Setters>
        </VisualState>
        <VisualState x:Name="Visible" />
    </VisualStateGroup>
    <VisualStateGroup x:Name="BusyStatusStates">
        <VisualState x:Name="Idle" />
        <VisualState x:Name="Busy">
            <VisualState.Setters>
                <Setter Target="content.(Control.IsEnabled)"
                        Value="False" />
            </VisualState.Setters>
        </VisualState>
    </VisualStateGroup>
</VisualStateManager.VisualStateGroups>

2.3 其它细节

<Setter Property="BusyContent"
        Value="Please wait..." />
<Setter Property="IsTabStop"
        Value="False" />
<Setter Property="OverlayStyle">
    <Setter.Value>
        <Style TargetType="Rectangle">
            <Setter Property="Fill"
                    Value="{ThemeResource ApplicationForegroundThemeBrush}" />
            <Setter Property="Opacity"
                    Value="0.2" />
        </Style>
    </Setter.Value>
</Setter>
<Setter Property="ProgressRingStyle">
    <Setter.Value>
        <Style TargetType="ProgressRing">
            <Setter Property="Height"
                    Value="50" />
            <Setter Property="Width"
                    Value="50" />
            <Setter Property="Margin"
                    Value="8,8,8,0" />
        </Style>
    </Setter.Value>
</Setter>
<Setter Property="DisplayAfter"
        Value="00:00:00.1" />
<Setter Property="HorizontalAlignment"
        Value="Stretch" />
<Setter Property="VerticalAlignment"
        Value="Stretch" />
<Setter Property="HorizontalContentAlignment"
        Value="Stretch" />
<Setter Property="VerticalContentAlignment"
        Value="Stretch" />

上面是BusyIndicator DefaultStyle的Setters，有一些细节是实现模板化控件需要注意的：

BusyContent

BusyContent没有在依赖属性定义中的PropertyMetadata给出默认值，而是在Setter中给出，这是模板化控件中依赖属性的最佳做法。PropertyMetadata的默认值应该尽量做到：值类型使用值类型的默认值，引用类型使用Null。

IsTabStop

已经不厌其烦地提醒过复合类型控件要将IsTabStop设置为False，以便在使用键盘导航时其内容可以直接获得焦点。

OverlayStyle和ProgressRingStyle

复合类型控件通常都会像这样为里面某个元素提供Style的属性，代替提供一大堆OverlayBackground，OverlayOpacity等属性。为了使用户清楚这两个Style属性对应的TargetType，可以在BusyIndicator的类型声明上使用StyleTypedPropertyAttribute：

[StyleTypedProperty(Property = "OverlayStyle", StyleTargetType = typeof(Rectangle))]
[StyleTypedProperty(Property = "ProgressRingStyle", StyleTargetType = typeof(ProgressRing))]

IsTabStop和StyleTypedPropertyAttribute的介绍都可见我另一篇文章：了解模板化控件(9)：UI指南

HorizontalContentAlignment和VerticalContentAlignment

使用ContentControl时几乎每次都要设置HorizontalContentAlignment和VerticalContentAlignment为Stretch，SilverlightToolkit中BusyIndicator的作者就很清楚这点。

这两个属性和BusyContent不同，并不是BusyIndicator定义的，而是从父类继承而来。像这种从父类继承而来的属性通常不会在构造函数中设置默认值，而是在DefaultStyle的Setter中设置默认值。

2.4 运行效果

就这样一个BusyIndicator就移植成功了。由于代码部分基本没有改变（除了ProgressBarStyle改成ProgressRingStyle），应该不会出什么大问题。运行效果如下：

<busyIndicatorSample:BusyIndicator x:Name="BusyIndicator">
    <Button HorizontalAlignment="Center"
            VerticalAlignment="Center"
            Content="Login"
            Click="Button_Click"
            Margin="0,0,0,150" />
</busyIndicatorSample:BusyIndicator>

private async void Button_Click(object sender, RoutedEventArgs e)
{
    BusyIndicator.IsBusy = true;
    await Task.Delay(TimeSpan.FromSeconds(3));
    BusyIndicator.IsBusy = false;
}

3. 来点调皮的

突然来了点兴致，于是就派生出新的控件ExtendBusyIndicator并新增public object BusyInformation{ get; set; }和public object IdleInformation{ get; set; }两个属性，运行效果如下：

XAML:

<busyIndicatorSample:ExtendBusyIndicator x:Name="BusyIndicator"
                                         Background="White">
    <busyIndicatorSample:ExtendBusyIndicator.BusyInformation>
        <StackPanel>
            <TextBlock Text="十年后"
                       HorizontalAlignment="Center" />
            <TextBlock Text="10 years later"
                       HorizontalAlignment="Center"
                       Margin="0,2,0,0" />
        </StackPanel>
    </busyIndicatorSample:ExtendBusyIndicator.BusyInformation>
    <busyIndicatorSample:ExtendBusyIndicator.IdleInformation>
        <StackPanel>
            <TextBlock Text="这个网页终于加载完了"
                       HorizontalAlignment="Center" />
            <TextBlock Text="the Web page finally finished loading."
                       HorizontalAlignment="Center"
                       Margin="0,2,0,0" />
        </StackPanel>
    </busyIndicatorSample:ExtendBusyIndicator.IdleInformation>

    <Button Style="{StaticResource ButtonRevealStyle}"
            Padding="0"
            HorizontalAlignment="Center"
            Background="Transparent"
            Margin="0,0,0,150"
            Click="Button_Click">
        <Image Source="logo1.png"
               Width="80" />
    </Button>
</busyIndicatorSample:ExtendBusyIndicator>

4. 莓良心的

5. 结语

BusyIndicator十分实用，毕竟已经经过多年的考验而代码基本没有更改，应该可以使用在UWP的实际项目中。

其实我个人不是很喜欢IsBusy就将Content.IsEnabled设置成False这么简单粗暴，因为这样内容会变成灰色。而且busyContent显示的过程应该是个透明度渐变的过程。这两个点使得执行很快的操作会令UI闪烁一下。而且ControlTemplate中ProgressRing和Overlay的父元素是一个叫busyContent的Grid，但BusyContent（注意大小些）是BusyIndicator的一个属性，内容是Busy状态下显示的文字内容，这样很容易让人混淆。幸运的是模板化控件最大的特色就是对修改UI是开放的，将来可以想办法修改。

ExtendBusyIndicator就算了，闹着玩的。

6. 参考

Extended WPF Toolkit

Silverlight Toolkit - CodePlex Archive

UWP BusyIndicator · telerik UI For UWP

7. 源码

BusyIndicatorSample