If your custom binding is not recognized by MvvmCross, there are several steps you can take to troubleshoot and resolve the issue:
1. Verify Binding Convention**
Ensure that your custom control follows the standard MvvmCross binding convention. MvvmCross typically binds to public properties using reflection. If your control uses arbitrary get/set methods instead of properties, or signals changes using a delegate instead of an event, you may need to create a custom binding[2].2. Create a Custom Target Binding**
To bind to a custom view or property that MvvmCross does not support out of the box, you need to create a custom target binding. This involves writing a class that inherits from `MvxPropertyInfoTargetBinding` or another appropriate subclass of `MvxTargetBinding`. This class will define how to set the property and handle events for two-way bindings[1].Here's an example of how you might define a custom target binding for a property named `MyProperty` on a view called `MyView`:
csharp
public class MyViewMyPropertyTargetBinding : MvxPropertyInfoTargetBinding
{
private bool _subscribed;
public override MvxBindingMode DefaultMode => MvxBindingMode.TwoWay;
public MyViewMyPropertyTargetBinding(object target, PropertyInfo targetPropertyInfo)
: base(target, targetPropertyInfo)
{
}
protected override void SetValueImpl(object target, object value)
{
var view = target as MyView;
if (view == null) return;
view.MyProperty = (string)value;
}
public override void SubscribeToEvents()
{
var myView = View;
if (myView == null)
{
MvxBindingTrace.Trace(MvxTraceLevel.Error, "Error - MyView is null in MyViewMyPropertyTargetBinding");
return;
}
_subscribed = true;
myView.MyPropertyChanged += HandleMyPropertyChanged;
}
private void HandleMyPropertyChanged(object sender, EventArgs e)
{
var myView = View;
if (myView == null) return;
FireValueChanged(myView.MyProperty);
}
protected override void Dispose(bool isDisposing)
{
base.Dispose(isDisposing);
if (isDisposing)
{
var myView = View;
if (myView != null && _subscribed)
{
myView.MyPropertyChanged -= HandleMyPropertyChanged;
_subscribed = false;
}
}
}
}
3. Register the Custom Binding**
After defining your custom target binding, you need to register it in your `Setup.cs` file. This is done by overriding the `FillTargetFactories` method and registering your binding using the `RegisterPropertyInfoBindingFactory` method:csharp
protected override void FillTargetFactories(IMvxTargetBindingFactoryRegistry registry)
{
base.FillTargetFactories(registry);
registry.RegisterPropertyInfoBindingFactory(
typeof(MyViewMyPropertyTargetBinding),
typeof(MyView), "MyProperty");
}
4. Check for Inflation Issues**
If you are using a custom control within another layout, ensure that you are inflating the view correctly. MvvmCross requires the use of `BindingInflate` instead of the standard `LayoutInflater` to properly set up bindings[5].5. Verify Event Handling**
Make sure that the events you are listening to are correctly firing and that your binding is properly handling these events. If your control does not raise a standard `PropertyChanged` event, you may need to manually handle this in your custom binding[1].6. Debugging**
Use debugging tools to verify that your binding is being created and that events are being handled as expected. Check for any error messages in the output that might indicate why the binding is not working.By following these steps, you should be able to resolve issues with custom bindings not being recognized by MvvmCross.
Citations:[1] https://www.mvvmcross.com/documentation/advanced/custom-data-binding
[2] http://slodge.blogspot.com/2013/06/n28-custom-bindings-n1-days-of-mvvmcross.html
[3] https://stackoverflow.com/questions/29990428/unable-to-bind-custom-mvvmcross-views
[4] https://github.com/MvvmCross/MvvmCross/issues/3654
[5] https://stackoverflow.com/questions/28993136/mvvmcross-custom-control-and-binding
[6] https://learn.microsoft.com/en-us/mem/intune/developer/app-sdk-xamarin
[7] https://stackoverflow.com/questions/45169052/mvvmcross-data-binding-not-working
[8] https://www.mvvmcross.com/documentation/advanced/customizing-using-App-and-Setup
[9] http://stackoverflow.com/questions/10700445/in-mvvmcross-how-do-i-do-custom.-bind-properties
[10] https://www.mvvmcross.com/documentation/plugins/methodbinding