Xamarin Forms Creating Custom Views And Controls Complete Guide

Last Update:2025-06-23T00:00:00 .NET School AI Teacher - SELECT ANY TEXT TO EXPLANATION. 7 mins read Difficulty-Level: beginner

Understanding the Core Concepts of Xamarin Forms Creating Custom Views and Controls

Creating Custom Views and Controls in Xamarin.Forms

Understanding Custom Views vs Custom Controls

Custom Views:
- These are typically used when you need to combine existing controls into a new, re-usable, custom component.
- Examples include creating composite views like a LoginView combining an Entry, a PasswordEntry, and a Button.
Custom Controls:
- Used when you need to extend or modify the behavior and rendering of existing controls.
- Useful when built-in control properties do not satisfy your needs, such as adding additional gestures or changing the look and feel significantly.

Creating a Custom View

Let's walk through creating a simple custom view which includes a Label, an Entry, and a Button.

Step 1: Create a New Class

In your Xamarin.Forms project, create a new class for your custom view:

public class LoginView : StackLayout
{
    public readonly Entry EmailEntry;
    public readonly Entry PasswordEntry;
    public readonly Button LoginButton;

    public LoginView()
    {
        // Initialize all the necessary UI elements
        Label titleLabel = new Label { Text = "Login", HorizontalOptions = LayoutOptions.Center };
        EmailEntry = new Entry { Placeholder = "Email" };
        PasswordEntry = new Entry { Placeholder = "Password", IsPassword = true };
        LoginButton = new Button { Text = "Log In" };

        // Add UI elements to the layout
        Children.Add(titleLabel);
        Children.Add(EmailEntry);
        Children.Add(PasswordEntry);
        Children.Add(LoginButton);
    }
}

Step 2: Use Your Custom View

You can now use LoginView in your XAML or code-behind:

In Code-Behind

var loginView = new LoginView();
loginView.EmailEntry.TextChanged += Entry_TextChanged;
loginView.PasswordEntry.TextChanged += Entry_TextChanged;
loginView.LoginButton.Clicked += LoginButton_Clicked;

void Entry_TextChanged(object sender, TextChangedEventArgs e)
{
    // Handle text change events
}

void LoginButton_Clicked(object sender, EventArgs e)
{
    // Handle button click events
}

ContentPage.Content = loginView;

In XAML Ensure you add a namespace reference to your custom control if it’s defined in a different assembly:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:YourNamespace;assembly=YourAssembly"
             x:Class="YourApp.MainPage">
    <local:LoginView />
</ContentPage>

Creating a Custom Control

Creating a custom control involves subclassing an existing control and overriding its methods or properties to achieve the desired functionality. Let's illustrate how to create a custom Entry control which changes its background color based on whether it’s focused or not.

Step 1: Subclass the Existing Control

Create a new class by inheriting from the built-in Entry:

public class ColorEntry : Entry
{
    private Color _defaultBackgroundColor;

    public ColorEntry()
    {
        _defaultBackgroundColor = BackgroundColor;

        Unfocused += (sender, e) => BackgroundColor = _defaultBackgroundColor;
        Focused += (sender, e) => BackgroundColor = Color.LightBlue;
    }
}

Step 2: Use Your Custom Control

You can utilize ColorEntry in your XAML or code-behind as follows:

In Code-Behind

var emailEntry = new ColorEntry 
{ 
    Placeholder = "Email",
    HorizontalOptions = LayoutOptions.FillAndExpand 
};
var passwordEntry = new ColorEntry 
{ 
    Placeholder = "Password",
    IsPassword = true,
    HorizontalOptions = LayoutOptions.FillAndExpand 
};

StackLayout mainLayout = new StackLayout
{
    Children = { emailEntry, passwordEntry }
};
ContentPage.Content = mainLayout;

In XAML Ensure your namespace references the custom control:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:YourNamespace;assembly=YourAssembly"
             x:Class="YourApp.MainPage">
    <local:ColorEntry Placeholder="Email" HorizontalOptions="FillAndExpand" />
    <local:ColorEntry Placeholder="Password" IsPassword="True" HorizontalOptions="FillAndExpand" />
</ContentPage>

Important Information

Performance Consideration: Custom controls and views should be performance-optimized. Avoid unnecessary operations and memory allocations during the render process.
Cross-Platform Compatibility: Ensure your custom controls work across all supported platforms (iOS, Android, Windows UWP). This might involve handling platform-specific logic using techniques like Dependency Services.
Maintainability: Write clean and well-commented code. Modularize your custom views or controls so they can be easily extended, reused, and tested.

Use Bindable Properties: Make your custom controls flexible by using bindable properties:

public static readonly BindableProperty ColorOnFocusProperty = 
    BindableProperty.Create(nameof(ColorOnFocus), typeof(Color), typeof(ColorEntry), Color.LightBlue);

public Color ColorOnFocus
{
    get => (Color)GetValue(ColorOnFocusProperty);
    set => SetValue(ColorOnFocusProperty, value);
}

public ColorEntry()
{
    Focused += (sender, e) => BackgroundColor = ColorOnFocus;
    Unfocused += (sender, e) => BackgroundColor = _defaultBackgroundColor;
}

Validation: Implement validation logic within your custom controls to ensure data integrity.
Testing: Thoroughly test your custom components across devices to catch any issues related to platform variations.
Documentation: Provide documentation and examples for your custom controls/views to make them easier to understand and use for other developers on your team.

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Step-by-Step Guide: How to Implement Xamarin Forms Creating Custom Views and Controls

Example 1: Creating a Custom View

In this example, we'll create a custom view that combines a Label and an Image to show a profile picture with a name below it.

Step 1: Create a New Xamarin.Forms Project

Open Visual Studio.
Go to File -> New -> Project.
Select Mobile App (Xamarin.Forms).
Choose a template, such as Blank, and set the project name (e.g., CustomViewDemo).

Step 2: Define the Custom View

Create a new class that inherits from ContentView. This will be our custom view.

Right-click on the Shared Project (e.g., CustomViewDemo) and select Add -> New Class.
Name the class ProfilePicture.

using System;
using Xamarin.Forms;

namespace CustomViewDemo
{
    public class ProfilePicture : ContentView
    {
        // Properties
        public static readonly BindableProperty ProfileNameProperty =
            BindableProperty.Create(
                nameof(ProfileName),
                typeof(string),
                typeof(ProfilePicture),
                string.Empty,
                BindingMode.OneWay,
                propertyChanged: OnProfileNamePropertyChanged);

        public static readonly BindableProperty ImageSourceProperty =
            BindableProperty.Create(
                nameof(ImageSource),
                typeof(ImageSource),
                typeof(ProfilePicture),
                default(ImageSource),
                BindingMode.OneWay,
                propertyChanged: OnImageSourcePropertyChanged);

        public string ProfileName
        {
            get => (string)GetValue(ProfileNameProperty);
            set => SetValue(ProfileNameProperty, value);
        }

        public ImageSource ImageSource
        {
            get => (ImageSource)GetValue(ImageSourceProperty);
            set => SetValue(ImageSourceProperty, value);
        }

        private Label nameLabel;
        private Image profileImage;

        // Constructor
        public ProfilePicture()
        {
            profileImage = new Image { Aspect = Aspect.AspectFill, WidthRequest = 100, HeightRequest = 100 };
            nameLabel = new Label { HorizontalTextAlignment = TextAlignment.Center };

            var stackLayout = new StackLayout
            {
                Children = { profileImage, nameLabel },
                Padding = new Thickness(10)
            };

            Content = stackLayout;
        }

        // Property changed callbacks
        private static void OnProfileNamePropertyChanged(BindableObject bindable, object oldValue, object newValue)
        {
            var control = (ProfilePicture)bindable;
            control.nameLabel.Text = newValue.ToString();
        }

        private static void OnImageSourcePropertyChanged(BindableObject bindable, object oldValue, object newValue)
        {
            var control = (ProfilePicture)bindable;
            control.profileImage.Source = (ImageSource)newValue;
        }
    }
}

Step 3: Use the Custom View

Now, use the ProfilePicture view inside your main page or any other page in your application.

Open the MainPage.xaml file in your Shared project.
Add the namespace declaration to use the custom view at the top.
Use the custom view inside the layout.

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:CustomViewDemo"
             x:Class="CustomViewDemo.MainPage">

    <StackLayout VerticalOptions="CenterAndExpand" HorizontalOptions="CenterAndExpand">
        <local:ProfilePicture ProfileName="John Doe" ImageSource="profile.png" />
    </StackLayout>
</ContentPage>

Step 4: Add Images to Each Platform Project

You'll need to add the image used in the ProfilePicture custom view to each platform project.

Android:
- Go to the Resources/drawable folder and add the image named profile.png.
iOS:
- Go to the Assets.xcassets folder and add the image named profile.png.
UWP:
- Go to the root of the project (not the shared one), create or find a Assets folder and add the image named profile.png.

Example 2: Creating a Custom Control

We'll create a toggle button that changes its background color based on its state (pressed or not pressed).

Step 1: Define the Custom Control

In the Shared Project, add a new class named ColorToggleButton.
It should inherit from Button and handle the background color change on press and release.

using System;
using Xamarin.Forms;

namespace CustomViewDemo
{
    public class ColorToggleButton : Button
    {
        private Color defaultColor;
        private Color pressedColor;

        public ColorToggleButton()
        {
            defaultColor = Color.LightGray;
            pressedColor = Color.DarkGray;

            BackgroundColor = defaultColor;

            Pressed += (s, e) => { BackgroundColor = pressedColor; };
            Released += (s, e) => { BackgroundColor = defaultColor; };
        }

        public Color TogglePressedColor
        {
            get => pressedColor;
            set
            {
                pressedColor = value;
                if (IsPressed)
                    BackgroundColor = value;
            }
        }

        public Color ToggleDefaultColor
        {
            get => defaultColor;
            set
            {
                defaultColor = value;
                if (!IsPressed)
                    BackgroundColor = value;
            }
        }
    }
}

Step 2: Use the Custom Control

Now, use the ColorToggleButton inside your main page or any other page in your application.

Open MainPage.xaml.
Include the namespace and add the component:

Top 10 Interview Questions & Answers on Xamarin Forms Creating Custom Views and Controls

Top 10 Questions & Answers on Xamarin.Forms: Creating Custom Views and Controls

1. What is the purpose of creating custom views and controls in Xamarin.Forms?

2. How can you create a simple custom view in Xamarin.Forms?

Answer: To create a simple custom view:

Step 1: Create a new class in your shared project that inherits from ContentView or any other suitable base class like View.
Step 2: Override the OnSizeAllocated() method if you need custom layout behavior.
Step 3: In XAML or C#, define the appearance and behavior of your custom view using standard Xamarin.Forms controls.

public class CustomCircleView : ContentView
{
    public static readonly BindableProperty CircleColorProperty = 
        BindableProperty.Create(nameof(CircleColor), typeof(Color), typeof(CustomCircleView), Color.Default);

    public Color CircleColor
    {
        get => (Color)GetValue(CircleColorProperty);
        set => SetValue(CircleColorProperty, value);
    }

    public CustomCircleView()
    {
        var boxView = new BoxView{ Color = CircleColor };
        Content = boxView;
    }

    protected override void OnSizeAllocated(double width, double height)
    {
        base.OnSizeAllocated(width, height);
        Content.LayoutTo(new Rectangle(0, 0, width, height));
        ((BoxView)Content).HeightRequest = width;
        ((BoxView)Content).WidthRequest = width;
    }
}

3. How do you render platform-specific custom views using the `IViewRenderer` interface?

Answer: The IViewRenderer interface is specific to older versions of Xamarin.Forms and has been replaced by IVisualElementRenderer. To create platform-specific custom renderers:

Step 1: Define an abstract control in your shared project.
Step 2: Create renderer classes for each target platform (iOS, Android, etc.), inheriting from IVisualElementRenderer<T>.
Step 3: Override methods and properties as needed to provide platform-specific functionality and UI enhancements.

Example on Android:

[assembly: ExportRenderer(typeof(CustomCircleView), typeof(AndroidCustomCircleViewRenderer))]
namespace MyApp.Droid
{
    public class AndroidCustomCircleViewRenderer : ViewRenderer<CustomCircleView, Android.Views.View>
    {
        protected override void OnElementChanged(ElementChangedEventArgs<CustomCircleView> e)
        {
            base.OnElementChanged(e);
            if(e.NewElement != null)
            {
                // Instantiate the native control here
                SetNativeControl(new Android.Views.View(Context));
            }
        }
        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);
            // Handle property changes here
        }
    }
}

4. Can you explain how to use native custom controls within Xamarin.Forms?

Answer: Yes, embedding native custom controls into Xamarin.Forms requires creating custom renderers.

Step 1: Define an abstract control in your shared project, which will act as a placeholder.
Step 2: Implement renderer classes targeting each platform where the native control exists.
Step 3: Use the SetNativeControl() method within the renderer’s OnElementChanged() method to instantiate the native control.

Example on iOS:

[assembly: ExportRenderer(typeof(CustomNativeView), typeof(iOSCustomNativeViewRenderer))]
namespace MyApp.iOS
{
    public class iOSCustomNativeViewRenderer : ViewRenderer<CustomNativeView, NativeViewClass>
    {
        protected override void OnElementChanged(ElementChangedEventArgs<CustomNativeView> e)
        {
            base.OnElementChanged(e);
            if (e.NewElement != null && Control == null)
            {
                SetNativeControl(new NativeViewClass());
            }
        }
    }
}

5. How do you handle property changes in your custom renderer?

Answer: Handle property changes by overriding the OnElementPropertyChanged() method in your renderer class. Check if the changed property is one you care about and update the native control accordingly.

protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
    base.OnElementPropertyChanged(sender, e);
    if (e.PropertyName == nameof(CustomCircleView.CircleColor))
    {
        ((BoxView)Control.Content).Color = Element.CircleColor;
    }
}

6. Why should you use `BindableProperties` in your custom controls?

Answer: BindableProperties enable data binding, allowing property changes to automatically propagate between the Xamarin.Forms layer and the native layer. This makes it easier to manage state and improve application maintainability and testability. BindableProperties also support features like styling and animations.

public static readonly BindableProperty TextColorProperty =
    BindableProperty.Create(
        nameof(TextColor),
        typeof(Color),
        typeof(MyCustomLabel),
        default(Color));

public Color TextColor
{
    get => (Color)GetValue(TextColorProperty);
    set => SetValue(TextColorProperty, value);
}

7. What are the advantages and disadvantages of creating custom controls versus using third-party libraries?

Answer: Advantages of Custom Controls:

Highly tailored to your app's exact needs.
Full control over performance and security aspects related to the rendering logic.
Better alignment with branding and visual guidelines of your app.

Disadvantages of Custom Controls:

Increased development time: Customizing controls often requires deep knowledge of each platform.
Higher maintenance burden: You’ll need to keep up with changes across platforms and Xamarin.Forms updates.
Riskier: Bugs introduced in custom renderers could be harder to diagnose and fix.

Advantages of Third-Party Libraries:

Saves time and resources as controls are already built and tested.
Access to more advanced UI features and capabilities.

Disadvantages of Third-Party Libraries:

Potential conflicts with your codebase.
Libraries may introduce unnecessary dependencies.
Harder to customize to meet specific requirements.

8. How do you ensure your custom controls work efficiently on all targeted platforms?

Answer: Ensuring efficiency involves:

Performance Optimization: Measure rendering times, memory usage, and optimize your rendering logic to handle these constraints.
Platform-Specific Code: Take advantage of native APIs on each platform, avoiding platform abstraction layers when they slow down performance.
Testing: Test thoroughly on all devices and versions of targeted operating systems.
Documentation and Community: Stay informed about best practices and follow community recommendations.

9. What are some common pitfalls when creating custom renderers in Xamarin.Forms?

Answer:

Incorrect Base Class: Ensure the custom renderer inherits from the correct base class corresponding to the Xamarin.Forms control.
Lifecycle Method Usage: Misuse of lifecycle methods like OnElementChanged() or OnElementPropertyChanged() can lead to errors such as memory leaks or inconsistent states.
Thread Issues: UI updates must happen on the main thread to avoid crashes. Be cautious with asynchronous operations that might affect the UI.
Device Compatibility: Native components behave differently on various device models. Test extensively across devices.

10. How can you style and theme your custom controls?

Answer: Styling and theming custom controls can be efficiently managed by:

Using Styles: Define styles in XAML and apply them to your custom controls. Styles allow setting multiple properties at once.
Custom Renderers: Override certain properties or methods in your custom renderer for better control over visual appearance.
Resource Dictionaries: Use resource dictionaries to centralize theme definitions.
Styling via Bindables: Leverage bindable properties in your custom controls to facilitate dynamic changes based on themes or styles.

Styling Example: