I’ve been doing a lot of mix development between Xamarin.Forms and Native Xamarin iOS/Android. Because of this, we abstract away concepts that can be shared regardless of using Xamarin.Forms or not. One thing I personally like, and use all the time, is Xamarin.Forms Behaviors. I wanted a way to use the same pattern with my native components. I went ahead and created NativeBehaviors.
Get it
- NuGet – https://www.nuget.org/packages/NativeBehaviors/
- GitHub – https://github.com/SuavePirate/NativeBehaviors
Concepts
Like mentioned above, we wanted to follow the same style as Xamarin.Forms Behaviors without having a dependency on Xamarin.Forms. You can create a NativeBehavior for any native control, and then handle attaching and detaching the behavior within the lifecycle of your ViewController, Activity, Fragment, etc.
This helps us keep our event handling cleaned up in memory while still being useful, easy to follow, re-usable, and flexible.
Documentation
Read below for the documentation on how to build your own NativeBehaviors and start making your controls more flexible!
NativeBehaviors
A behaviors implementation for Xamarin Native controls meant to reflect the usefulness of Xamarin.Forms.Behaviors
Installation
This project is up on NuGet now:
Install-Package NativeBehaviors
Usage
These behaviors are meant to reflect the same use as Xamarin.Forms Behaviors, but require a little more work to manage the lifecycle of events since native views don’t have a collection of Behaviors as a property.
- Create a custom Behavior on your native platform. This example will use an iOS
UITextField
TextFieldPhoneMaskBehavior.cs
/// <summary>
/// Text field phone mask behavior.
/// Format of (###) ###-####
/// </summary>
public class TextFieldPhoneMaskBehavior : NativeBehavior<UITextField>
{
public override string BehaviorName => nameof(TextFieldPhoneMaskBehavior);
private string _previousText = string.Empty;
/// <summary>
/// Attach text changed event
/// </summary>
/// <param name="bindable">Bindable.</param>
protected override void OnAttachedTo(UITextField bindable)
{
bindable.EditingChanged += Bindable_TextChanged;
}
/// <summary>
/// Detach event
/// </summary>
/// <param name="bindable">Bindable.</param>
protected override void OnDetachingFrom(UITextField bindable)
{
bindable.EditingChanged -= Bindable_TextChanged;
}
/// <summary>
/// Apply mask
/// </summary>
/// <param name="sender">Sender.</param>
/// <param name="e">E.</param>
void Bindable_TextChanged(object sender, EventArgs e)
{
var textField = sender as UITextField;
// only apply change if typing forward
if (textField != null && textField.Text.Length > _previousText.Length)
{
if (textField.Text.Length == 1)
{
// we have our first number, add the ( behind it
textField.Text = $"({textField.Text}";
}
if (textField.Text.Length == 4)
{
// finish the area code
textField.Text += ") ";
}
if (textField.Text.Length == 9)
{
// add dash
textField.Text += "-";
}
}
_previousText = textField.Text;
}
}
- Attach Behavior in lifecycle
MyViewController.cs
using NativeBehaviors; // needed for extension method
...
private TextFieldPhoneMaskBehavior _phoneMaskBehavior;
protected override void ViewWillAppear(bool animated)
{
...
_phoneMaskBehavior = new TextFieldPhoneMaskBehavior();
myTextField.AttachBehavior(_phoneMaskBehavior);
...
}
...
- Detach Behavior in lifecycle
MyViewController.cs
using NativeBehaviors; // needed for extension method
...
protected override void ViewDidDisappear()
{
...
myTextField.DetachBehavior(_phoneMaskBehavior);
...
}
...
Use the OnCreate and OnDestroy events in your Android Activities.
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Alex Dunn 
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