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Control Templates in Xamarin.Forms

December 13, 2021 - Rodrigo Juarez

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This is the second post in the custom control series. You can read the first one where we created a custom control to select dates.


In this second post in the series, I want to show you when and how to use control templates. A primary reason to use control templates is when you need additional content inserted into a custom control at a pre-defined location. You can define a common UI that also displays unique content in different places. Check the references section at the end of this post to see other uses of control templates, such as redefining a control’s UI.

For your reference, I added a container custom control to our code sample repository. It’s a view with a header and an icon that can be tapped. Our content will be shown after the header. The header and the icon can be hidden, and we can bind a command to the icon.

In the following image, you can see three different instances of the custom control, each one with its own content.

Control Template Implementation

Usually, you will define the control template as a resource in a resource dictionary. In the following XAML code, I defined a control template and used the Key property to apply it to the ContentView with the ControlTemplate property. Instead of using Binding, I used the TemplateBinding markup extension that allows me to bind the ControlTemplate to properties defined on the custom control.

For example, the HeaderTitle property, defined in our custom control, will be used to set the text of the header. Using the ContentPresenter, I can set the place where the user content will be displayed. See the ContentPresenter tag in the sample XAML code below.

<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="CustomControlsSample.Container"
             ControlTemplate="{DynamicResource ContainerTemplate}">
    <ContentView.Resources>

        <ResourceDictionary>

            <ControlTemplate x:Key="ContainerTemplate">
                <Frame Style="{DynamicResource FrameContainerStyle}">
                    <StackLayout Spacing="0">

                        <Grid Style="{DynamicResource BoxHeadTitleContainer}"
                            IsVisible="{TemplateBinding HeaderTitleIsVisible}">

                            <Label Style="{DynamicResource BoxHeadTitle}" Text="{TemplateBinding HeaderTitle}" />

                            <Image
                                Style="{DynamicResource BoxHeadIcon}"
                                IsVisible="{TemplateBinding IconIsVisible}">
                                <Image.Source>
                                    <!--Can't use style https://github.com/xamarin/Xamarin.Forms/issues/6421-->
                                    <FontImageSource
                                        Glyph="{TemplateBinding Icon}"
                                        Color="{DynamicResource BoxHeadTextColor}"
                                        FontFamily="FA"
                                        Size="18" />
                                </Image.Source>
                                <Image.GestureRecognizers>
                                    <TapGestureRecognizer Command="{TemplateBinding OnIconTappedCommand}"/>
                                </Image.GestureRecognizers>
                            </Image>

                        </Grid>

                        <StackLayout Style="{DynamicResource FrameContentStyle}">
                            <ContentPresenter />
                        </StackLayout>

                    </StackLayout>
                </Frame>
            </ControlTemplate>

        </ResourceDictionary>
    </ContentView.Resources>
</ContentView>

Consuming a Custom Control

In the MainPage.xaml file, you can see the use of the new custom control. Also, notice that I have the binding to MainPage’s command view model on line 6 to clean the dates when you tap on the icon, and the most important part, the user’s content starting in line 11 which will be shown inside the custom control. Notice that the line numbers I’m mentioning here are only for the partial code shown in this blog post, and not the full files in the code repository linked above.

.
.
.
<!--Select dates-->
<customcontrolssample:Container
    OnIconTappedCommand="{Binding CleanDate}"
    Icon="&#xf2ed;"
    IconIsVisible="True"
    HeaderTitle="Select your dates"
    HeaderTitleIsVisible="True">
    <StackLayout 
        Padding="16">
        <customcontrolssample:CustomDateTimePicker
        SelectedDateTime="{Binding StartDateTime, Mode=TwoWay}"
        Caption="Start Date"/>
        <customcontrolssample:CustomDateTimePicker
        SelectedDateTime="{Binding EndDateTime, Mode=TwoWay}"
        Caption="End Date"/>
    </StackLayout>
</customcontrolssample:Container>
.
.
.

Check out the references section below to learn about how to use custom fonts.

That’s all for now, please let me know what do you think in the comments section. Thanks for reading!

References

Control Templates

Custom Fonts in Xamarin.Forms

Rodrigo Juarez

I'm a full-stack and Xamarin Certified Mobile Professional developer. My mission is to solve complex problems for my clients focusing on the results, applying the most adequate technology available and best practices to ensure a cost-effective and high-quality solution. I have 20+ years of experience in a wide variety of projects in the development of applications for web, desktop, and mobile using Microsoft technologies in areas such as management, services, insurance, pharmacy, and banks.

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