MvvmCross UITextField custom binding

Question

So I am trying to implement a custom binding for a UITextField in MvvmCross, pretty much along the lines of Binding \'GO\' key on Software Keyboard - i.e. trying to bind a t

Answer 1

1. What is special about PropertyInfoTargetBinding?

The question you reference - MVVMCross Binding decimal to UITextField removes decimal point - gives the key to the difference between MvxTargetBinding and MvxPropertyInfoTargetBinding:

• TargetBinding can be used for any arbitrary binding - e.g. for a non-propertyInfo-based binding
• PropertyInfoTargetBinding inherits from TargetBinding and can only be used with actual C# Properties - because it uses PropertyInfo via Reflection.

In your case, since you aren't actually using the Text property via Reflection, then I'd be tempted not to use a PropertyInfoTargetBinding and to steer clear of the Text name as well - instead just write a custom TargetBinding.

the former is used when replacing an existing binding

This is definitely not true - instead any binding can be used to replace another binding - as the answer on the other question says

MvvmCross operates a simple 'last registered wins' system

For more on custom bindings, take a look at:

• the N=28 video in http://mvvmcross.blogspot.co.uk/
• take a look through some of the "standard" bindings that ship with MvvmCross
  • Droid - https://github.com/MvvmCross/MvvmCross/tree/v3.1/Cirrious/Cirrious.MvvmCross.Binding.Droid/Target
  • iOS - https://github.com/MvvmCross/MvvmCross/tree/v3.1/Cirrious/Cirrious.MvvmCross.Binding.Touch/Target
  • note that most of these use either MvxPropertyInfoTargetBinding or MvxConvertingTargetBinding as a base class

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2. Why is my SetValue getting null?

Your current binding code is asking for an ICommand:

public override Type TargetType
{
    get { return typeof(ICommand); }
}

But your View code is currently binding the View to a string:

// View
set.Bind(usernameTextField).To(vm => vm.Username);

// ViewModel
private string _username;
public string Username
{ 
    get { return _username; }
    set { _username = value; RaisePropertyChanged(() => Username); }
}

To solve this...

1. Work out what you want to bind to - is it an ICommand (e.g. and MvxCommand) or is it a string?
2. Change the View and the Binding to reflect this.