Since Xamarin Android doesn't provide some method to automatically generate properties for subviews in your layout, ReactiveUI provides a helper method to do this for you. Every Activity, Fragment, View or class implementing ILayoutViewHost can call the extensions method WireUpControls with one of three ways to resolve properties to their respective element in the layout.

It works in a similar fashion to Butterknife for Android.

Naming policies

When calling WireUpControls from your application, a dictionary is built of all resource ID names used in your layouts, converted to lowercase, mapped to the actual resource ID. Essentially it's based on the contents of the Resource.designer.cs file.

Because the dictionary is indexed on the lowercase variant of the name, you can't use the same resouce name twice in your layouts with different casings. Android is case-sensitive when generating resource ID's, thus making it impossbile to map this to a single resource ID for use with WireUpControls.

The reason this is mapping is made, is because you would often use camelCase names in your layout files with a lower case first letter. While in your classes, properties should use an upper case first letter.

So while you can use the same resource name multiple times in a single or multiple layout files like you normally can, they would have to use the exact same casing.

Resolving strategies

You can choose from three different ResolveStrategy options when calling WireUpControls, of which the default implicit variant will work in most cases, but for specialized cases we also provide two explicit strategies.

Implicit

This is the default. WireUpControls tries to resolve every property that is a subclass of View in your class to a resource ID in your layout, regardless of visibility. Since your view should mainly be responsible for data-binding and not much else, this shouldn't impose a lot of problems. Mind you that properties of type View will be ignored since this causes propblems with default properties already present in activities for example.

Explicit opt-in

In this case, you'll need to decorate properties you want to have wired up with the WireUpResource attribute. Every other property will be ignored by WireUpControls. No type-checking is imposed.

Explicit opt-out

In this case, every property will be mapped to a resource ID in your layout file, unless it's decorated with the IgnoreResource attribute. This applies to all properties with a type of View, and subclasses thereof.

Examples

For this layout:

<?xml version="1.0" encoding="utf-8"?>
  <LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
  <EditText
    android:id="@+id/TheEditText"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />
  <TextView
    android:id="@+id/TheTextView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />
</LinearLayout>

ControlFetcherMixin.ResolveStrategy.Implicit

[Activity (Label = "WireUpControls-Sample", MainLauncher = true)]
public class TestActivity : ReactiveActivity<TheViewModel> 
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        SetContentView(Resource.Layout.Main);

        this.WireUpControls(ControlFetcherMixin.ResolveStrategy.Implicit);

        ViewModel = new TheViewModel();

        this.Bind(this.ViewModel, x => x.TheText, x => x.TheEditText.Text);
        this.OneWayBind(this.ViewModel, x => x.TheText, x => x.TheTextView.Text);
    }

    public EditText TheEditText { get; private set; }

    public TextView TheTextView { get; private set; }
}

ControlFetcherMixin.ResolveStrategy.ExplicitOptIn

[Activity (Label = "WireUpControls-Sample", MainLauncher = true)]
public class TestActivity : ReactiveActivity<TheViewModel>
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        SetContentView(Resource.Layout.Main);

        this.WireUpControls(ControlFetcherMixin.ResolveStrategy.ExplicitOptIn);

        ViewModel = new TheViewModel();

        this.Bind(this.ViewModel, x => x.TheText, x => x.TheEditText.Text);
        this.OneWayBind(this.ViewModel, x => x.TheText, x => x.TheTextView.Text);
    }

    [WireUpResource]
    public EditText TheEditText { get; private set; }

    [WireUpResource("TheTextView")
    public TextView AwesomeTextView { get; private set; }
}

ControlFetcherMixin.ResolveStrategy.ExplicitOptOut

[Activity (Label = "WireUpControls-Sample", MainLauncher = true)]
public class TestActivity : ReactiveActivity<TheViewModel>
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        SetContentView(Resource.Layout.Main);

        this.WireUpControls(ControlFetcherMixin.ResolveStrategy.ExplicitOptOut);

        ViewModel = new TheViewModel();

        this.Bind(this.ViewModel, x => x.TheText, x => x.TheEditText.Text);
        this.OneWayBind(this.ViewModel, x => x.TheText, x => x.TheTextView.Text);
    }

    public EditText TheEditText { get; private set; }

    public TextView TheTextView { get; private set; }

    [IgnoreResource]
    public View SomeTempView { get; private set; }
}