[UWP]实现Picker控件

1. 前言

在WPF中,很多打开下拉框(Popup或Flyout)选择一个结果值的控件,除了ComboBox等少数例外,这种控件都以-Picker做名称后缀。因为要打开关闭下拉框和计算下拉框的弹出位置, 这类控件实现起来还挺麻烦的。Silverlight Toolkit中贴心地提供了一个Picker控件,可以作为这类控件的基类,省略了大量代码。

2. 现在的问题

由于UWP中有Flyout,-Picker控件的实现其实算是相当轻松的。如ColorPicker的官方文档就介绍了使用Flyout承载ColorPicker的实现代码。但是做起来还是有一些问题:

  1. 在有“确定/取消”按钮的Flyout中,即使选择了值,如果没有点击“确定”按钮也不更新结果值。
  2. 在Flyout打开的状态,还是希望它所属的按钮有某种已被按下的状态显示,典型的如ComboBox、Extended WPF Toolkit的ColorPicker、WinForm的DateTimePicker,或其它大部分Windows的控件那样:

上面第一点是硬性要求,所有-Picker类控件都会实现这点(偶尔也见到没做好的)。第二点就比较麻烦了,UWP几乎完全没有理会这点。其实WPF/Silverlight时代即已经开始忽略这点UI需求了,但我还是希望可以注意这些UI的细节,毕竟UWP就经常被诟病UI细节缺失。

3. 我的解决方案

于是我决定实现一个UWP的Picker类。

3.1 定义外观

SilverlightToolkit的Picker相当复杂,UI有三个VisualStateGroup,两个TemplatPart:

[TemplateVisualState(GroupName = "PopupStates", Name = "PopupClosed")]
[TemplatePart(Name = "DropDownToggle", Type = typeof (ToggleButton))]
[TemplateVisualState(GroupName = "PopupStates", Name = "PopupOpened")]
[TemplateVisualState(GroupName = "CommonStates", Name = "Normal")]
[TemplateVisualState(GroupName = "CommonStates", Name = "MouseOver")]
[TemplateVisualState(GroupName = "CommonStates", Name = "Pressed")]
[TemplateVisualState(GroupName = "CommonStates", Name = "Disabled")]
[TemplateVisualState(GroupName = "FocusStates", Name = "Focused")]
[TemplateVisualState(GroupName = "FocusStates", Name = "Unfocused")]
[TemplatePart(Name = "Popup", Type = typeof (Popup))]
public abstract class Picker : Control, IUpdateVisualState

我不想做到这么复杂,只有一个名为PopupStatesName的VisualStateGroup(沿用Silverlight Toolkit的命名),一个Flyout,一组“确定/取消”按钮就够了。

[TemplateVisualState(Name = PopupClosedName, GroupName = PopupStatesName)]
[TemplateVisualState(Name = PopupOpenedName, GroupName = PopupStatesName)]
[TemplatePart(Name = AcceptButtonName, Type = typeof(Button))]
[TemplatePart(Name = DismissButtonName, Type = typeof(Button))]
[TemplatePart(Name = FlyoutName, Type = typeof(FlyoutBase))]
public abstract class Picker : HeaderedContentControl
{
    private const string PopupClosedName = "PopupClosed";
    private const string PopupOpenedName = "PopupOpened";
    private const string PopupStatesName = "PopupStates";


    private const string FlyoutName = "Flyout";
    private const string AcceptButtonName = "AcceptButton";
    private const string DismissButtonName = "DismissButton";

此为下文中MyDatePicker的运行效果。

3.2 IsOpen属性

Picker中提供一个bool IsDropDownOpen属性,用于控制下拉框是否打开。无论是AcceptButton或DismissButton的点击事件,或者Flyout的Closed事件都会调用这个属性。

protected virtual void OnIsDropDownOpenChanged(bool oldValue, bool newValue)
{
    if (_flyout == null)
        return;

    if (newValue)
        _flyout.ShowAt(this);
    else
        _flyout.Hide();
}

protected virtual void OnFlyoutClosed(object e)
{
    IsDropDownOpen = false;
}

protected virtual void OnAccept(RoutedEventArgs e)
{
    IsDropDownOpen = false;
}

protected virtual void OnDismiss(RoutedEventArgs e)
{
    IsDropDownOpen = false;
}

protected override void UpdateVisualState(bool useTransitions)
{
    base.UpdateVisualState(useTransitions);
    VisualStateManager.GoToState(this, IsDropDownOpen ? PopupOpenedName : PopupClosedName, useTransitions);
}

3.3 实际应用:实现一个MyDatePicker

需要实现一个MyDatePicker,可以继承Picker,Default Style如下,不少内容都是参考DatePicker:

<Style TargetType="local:MyDatePicker">
    <Setter Property="IsTabStop"
            Value="False" />
    <Setter Property="FontFamily"
            Value="{ThemeResource ContentControlThemeFontFamily}" />
    <Setter Property="FontSize"
            Value="{ThemeResource ControlContentThemeFontSize}" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="local:MyDatePicker">
                <StackPanel x:Name="LayoutRoot"
                            Margin="{TemplateBinding Padding}">
                    <local:HeaderedContentControl Header="{TemplateBinding Header}"
                                                  HeaderTemplate="{TemplateBinding HeaderTemplate}">
                        <ToggleButton x:Name="DateButton"
                                      Content="{TemplateBinding DateTime}"
                                      IsEnabled="{TemplateBinding IsEnabled}"
                                      IsChecked="{Binding RelativeSource={RelativeSource Mode=TemplatedParent}, Path=IsDropDownOpen,Mode=TwoWay}"
                                      HorizontalAlignment="Stretch"
                                      HorizontalContentAlignment="Stretch">
                            <FlyoutBase.AttachedFlyout>
                                <Flyout Placement="Bottom"
                                        x:Name="Flyout">
                                    <Flyout.FlyoutPresenterStyle>
                                        <Style TargetType="FlyoutPresenter">
                                            <Setter Property="Padding"
                                                    Value="0" />
                                            <Setter Property="BorderThickness"
                                                    Value="0" />
                                            <Setter Property="Template">
                                                <Setter.Value>
                                                    <ControlTemplate TargetType="FlyoutPresenter">
                                                        <ContentPresenter Background="{TemplateBinding Background}"
                                                                          BorderBrush="{TemplateBinding BorderBrush}"
                                                                          BorderThickness="{TemplateBinding BorderThickness}"
                                                                          Content="{TemplateBinding Content}"
                                                                          ContentTemplate="{TemplateBinding ContentTemplate}"
                                                                          ContentTransitions="{TemplateBinding ContentTransitions}"
                                                                          Margin="{TemplateBinding Padding}"
                                                                          HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                                                          VerticalAlignment="{TemplateBinding VerticalContentAlignment}" />
                                                    </ControlTemplate>
                                                </Setter.Value>
                                            </Setter>
                                        </Style>
                                    </Flyout.FlyoutPresenterStyle>
                                    <Grid>
                                        <Grid.RowDefinitions>
                                            <RowDefinition />
                                            <RowDefinition Height="Auto" />
                                        </Grid.RowDefinitions>
                                        <CalendarView x:Name="Calendar"
                                                      Style="{TemplateBinding CalendarViewStyle}" />
                                        <Grid Grid.Row="1"
                                              Height="45"
                                              x:Name="AcceptDismissHostGrid">
                                            <Grid.ColumnDefinitions>
                                                <ColumnDefinition Width="*" />
                                                <ColumnDefinition Width="*" />
                                            </Grid.ColumnDefinitions>
                                            <Button x:Name="AcceptButton"
                                                    Grid.Column="0"
                                                    Content="&#xE8FB;"
                                                    FontFamily="{ThemeResource SymbolThemeFontFamily}"
                                                    FontSize="16"
                                                    HorizontalAlignment="Stretch"
                                                    VerticalAlignment="Stretch"
                                                    Style="{StaticResource DateTimePickerFlyoutButtonStyle}"
                                                    Margin="0,2,0,0" />
                                            <Button x:Name="DismissButton"
                                                    Grid.Column="1"
                                                    Content="&#xE711;"
                                                    FontFamily="{ThemeResource SymbolThemeFontFamily}"
                                                    FontSize="16"
                                                    HorizontalAlignment="Stretch"
                                                    VerticalAlignment="Stretch"
                                                    Style="{StaticResource DateTimePickerFlyoutButtonStyle}"
                                                    Margin="0,2,0,0" />
                                        </Grid>
                                    </Grid>
                                </Flyout>
                            </FlyoutBase.AttachedFlyout>
                        </ToggleButton>
                    </local:HeaderedContentControl>
                </StackPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

注意这里的ToggleButton使用TwoWay Binding将IsChecked绑定到Picker的IsDropDownOpen属性,通过IsChecked属性与Flyout的Show/Hide关联起来。

另外,Flyout里放了一个CalendarView,用于选择日期。

在MyDatePicker.cs里除了属性,主要的内容是这段代码:

protected override void OnAccept(RoutedEventArgs e)
{
    base.OnAccept(e);
    if (_calendar != null && _calendar.SelectedDates.Any())
        DateTime = _calendar.SelectedDates.First().DateTime;
}

重写OnAccept(即点击AcceptButton触发的事件)并为DateTime选择值。

3.4 实际应用:实现一个MyTimePicker

使用TemplatePart的一个重要原则是:即使ControlTemplate中缺少声明的TemplatePart,模板化控件也不会报错,只会缺少部分功能。

根据这个原则实现的MyTimePicker就缺少了AcceptButton和DismissButton,因为使用了TimePickerFlyout,这个控件本身就有AcceptButton和DismissButton按钮。

<Style TargetType="local:MyTimePicker">
    <Setter Property="IsTabStop"
            Value="False" />
    <Setter Property="FontFamily"
            Value="{ThemeResource ContentControlThemeFontFamily}" />
    <Setter Property="FontSize"
            Value="{ThemeResource ControlContentThemeFontSize}" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="local:MyTimePicker">
                <StackPanel x:Name="LayoutRoot"
                            Margin="{TemplateBinding Padding}">
                    <local:HeaderedContentControl Header="{TemplateBinding Header}"
                                                  HeaderTemplate="{TemplateBinding HeaderTemplate}">
                        <ToggleButton x:Name="DateButton"
                                      Content="{Binding RelativeSource={RelativeSource Mode=TemplatedParent},Path=Time,Converter={StaticResource TimeSpanToStringConverter}}"
                                      IsEnabled="{TemplateBinding IsEnabled}"
                                      IsChecked="{Binding RelativeSource={RelativeSource Mode=TemplatedParent}, Path=IsDropDownOpen,Mode=TwoWay}"
                                      HorizontalAlignment="Stretch"
                                      HorizontalContentAlignment="Stretch">
                            <FlyoutBase.AttachedFlyout>
                                <TimePickerFlyout x:Name="Flyout"  Placement="Bottom"/>
                            </FlyoutBase.AttachedFlyout>
                        </ToggleButton>
                    </local:HeaderedContentControl>
                </StackPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
protected override void OnApplyTemplate()
{
    base.OnApplyTemplate();
    _timePickerFlyout = GetTemplateChild(FlyoutName) as TimePickerFlyout;
    if (_timePickerFlyout != null)
        _timePickerFlyout.TimePicked += OnTimePicked;

    UpdateTimePicerFlyoutPickedTime();
    UpdateVisualState(false);
}


protected virtual void OnTimeChanged(TimeSpan oldValue, TimeSpan newValue)
{
    UpdateTimePicerFlyoutPickedTime();
}

protected override void OnIsDropDownOpenChanged(bool oldValue, bool newValue
{
    base.OnIsDropDownOpenChanged(oldValue, newValue);
    if (newValue)
        UpdateTimePicerFlyoutPickedTime();
}

private void UpdateTimePicerFlyoutPickedTime()
{
    if (_timePickerFlyout != null)
        _timePickerFlyout.Time = Time;
}

private void OnTimePicked(TimePickerFlyout sender, TimePickedEventArgs args)
{
    Time = args.NewTime;
}

4. 结语

细心的话会发现Picker虽然定义了PopupStates这个VisualStateGroup,但从来没用到。其实这是为了将来可能会用到这个这组状态而预留的。值得一提的是Picker不止可以针对弹出Flyout的控件,将ToggleButton和它的Flyout换成Expander也一样适用。

有了Picker类后确实方便了很多。其实Silverlight虽然死了,但开源的Silverlight Toolkit中有不少内容都可用作参考。本来还想给出Silverlight Toolkit中Picker的源码地址作为参考,但最近CodePlex关闭服务了。有兴趣的人仍可直接下载Silverlight Toolkit的源码,毕竟还是挺有趣的。
Silverlight Toolkit - CodePlex Archive

5. 参考

Guidelines for date and time controls

6. 源码

PickerTest

posted @ 2018-02-07 10:14 dino.c 阅读(...) 评论(...) 编辑 收藏