Costumize style of the selected (current) FlyoutItem

问题

I've noticed that when I customize flyout item appearance like it says here in the docs, the current FlyoutItem is not marked anymore.

Snip of the code from docs to change the item appearance:

<Shell ...>
    ...
    <Shell.ItemTemplate>
        <DataTemplate>
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="0.2*" />
                    <ColumnDefinition Width="0.8*" />
                </Grid.ColumnDefinitions>
                <Image Source="{Binding FlyoutIcon}"
                       Margin="5"
                       HeightRequest="45" />
                <Label Grid.Column="1"
                       Text="{Binding Title}"
                       FontAttributes="Italic"
                       VerticalTextAlignment="Center" />
            </Grid>
        </DataTemplate>
    </Shell.ItemTemplate>
</Shell>

Screenshot before Shell.ItemTemplate
Screenshot after Shell.ItemTemplate

One would assume there must also be some kind of Shell.Current/Active/SelectedItemTemplate customization, but I can not find it.

Any ideas how I can customize current shell item appearance, or at least make the default item marking work with Shell.ItemTemplate?

回答1:

Unfortunately.From Xamarin.Forms - Xaminals sample , also occurs this phenomenon. This should be a limit of Shell FlyoutItem in Current version of XF.

<Shell.ItemTemplate>
    <DataTemplate >
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="0.2*" />
                <ColumnDefinition Width="0.8*" />
            </Grid.ColumnDefinitions>
            <Image Source="{Binding FlyoutIcon}"
                Margin="5"
                HeightRequest="45" />
            <Label Grid.Column="1"
                Text="{Binding Title}"
                FontAttributes="Italic"
                VerticalTextAlignment="Center" />
        </Grid>
    </DataTemplate>
</Shell.ItemTemplate>

If not using Shell.ItemTemplate , selectitem is marked:

Else selectitem is not marked :

===================================UPDATE================================

Solution:

If adding style to the template , can hold the selected state after selecting.

Shell.Resources: adding a FloutItemStyle.

<Style x:Key="FloutItemStyle" TargetType="Grid">
    <Setter Property="VisualStateManager.VisualStateGroups">
        <VisualStateGroupList>
            <VisualStateGroup x:Name="CommonStates">
                <VisualState x:Name="Normal" />
                <VisualState x:Name="Selected">
                    <VisualState.Setters>
                        <Setter Property="BackgroundColor" Value="Accent"/>
                    </VisualState.Setters>
                </VisualState>
            </VisualStateGroup>
        </VisualStateGroupList>
    </Setter>
</Style>

Using in Shell.ItemTemplate as follow:

<Shell.ItemTemplate>
    <DataTemplate >
        <Grid Style="{StaticResource FloutItemStyle}">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="0.2*" />
                <ColumnDefinition Width="0.8*" />
            </Grid.ColumnDefinitions>
            <Image Source="{Binding FlyoutIcon}"
        Margin="5"
        HeightRequest="45" />
            <Label Grid.Column="1"
        Text="{Binding Title}"
        FontAttributes="Italic"
        VerticalTextAlignment="Center" />
        </Grid>
    </DataTemplate>
</Shell.ItemTemplate>

Finally showing the effect:

回答2:

You can use a binding property. Create a custom grid

public class ShellItemGrid : Grid
{
    public static readonly BindableProperty SelectedColorProperty =       BindableProperty.Create("SelectedColor", typeof(Color), typeof(ShellItemGrid),Color.Transparent);

    public Color SelectedColor
    {
        get { return (Color)GetValue(SelectedColorProperty); }
        set { SetValue(SelectedColorProperty, value); }
    }
}

Define the style for the grid

<Shell.Resources>
    <Style x:Key="FlyoutItemStyle" TargetType="controls:ShellItemGrid">
        <Setter Property="VisualStateManager.VisualStateGroups">
            <VisualStateGroupList>
                <VisualStateGroup x:Name="CommonStates">                      
                    <VisualState x:Name="Selected">
                        <VisualState.Setters>
                            <Setter Property="SelectedColor" Value="Red"/>
                        </VisualState.Setters>
                    </VisualState>
                    <VisualState x:Name="Normal">
                        <VisualState.Setters>
                            <Setter Property="SelectedColor" Value="White"/>
                        </VisualState.Setters>
                    </VisualState>
                </VisualStateGroup>
            </VisualStateGroupList>
        </Setter>
    </Style>

Define the item template and bind the TextColor of the Label to the SelectedColor of the grid

<Shell.ItemTemplate>
    <DataTemplate>
        <controls:ShellItemGrid x:Name="mGrid" Style="{StaticResource FlyoutItemStyle}" >
            <Label HorizontalTextAlignment="Start" 
                   VerticalTextAlignment="Center"
                   Margin="20,10,0,10"
                   Text="{Binding Title}"                        
                   TextColor="{Binding Source={x:Reference mGrid},Path=SelectedColor}"
                   FontSize="18" />
            </controls:ShellItemGrid >
    </DataTemplate>

</Shell.ItemTemplate>

来源：https://stackoverflow.com/questions/57421964/costumize-style-of-the-selected-current-flyoutitem