BindableProperty non-static method name enhancement

[stephenquan]

Instead of asking developers to write static methods for source generators, we could make things easier by letting them use regular instance methods. The benefit is that the methods are simpler, requiring no BindableProperty parameter or manual casting to the class type, since the source generator handles this automatically.

For example:

public partial class TestClassName : View
{
    [BindableProperty(
        DefaultValue = 42,
        ValidateValueMethodName = "ValidateValue",
        PropertyChangedMethodName = "OnPropertyChanged",
        PropertyChangingMethodName = "OnPropertyChanging",
        CoerceValueMethodName = "CoerceValue",
        DefaultValueCreatorMethodName = "CreateDefaultValue")]
     public partial int Value { get; set; }

     bool ValidateValue(object value) => true;
     void OnPropertyChanged(object oldValue, object newValue) { }
     void OnPropertyChanging(object oldValue, object newValue) { }
     object CoerceValue(object value) => value;
     object CreateDefaultValue() => 0;
}

Would generate a wrapper that includes the BindableObject bindable property:

public partial class TestClassName
{
    /// <summary>
    /// Backing BindableProperty for the <see cref = "Value"/> property.
    /// </summary>
    public static readonly global::Microsoft.Maui.Controls.BindableProperty ValueProperty = global::Microsoft.Maui.Controls.BindableProperty.Create(
       "Value",
       typeof(int),
       typeof(TestNamespace.TestClassName),
       (int)42,
       (Microsoft.Maui.Controls.BindingMode)1,
       (b,v) => ((TestClassName)b).ValidateValue(v),
       (b,o,n) => ((TestClassName)b).OnPropertyChanged(o,n),
       (b,o,n) => ((TestClassName)b).OnPropertyChanging(o,n),
       (b,v) => ((TestClassName)b).CoerceValue(v),
       (b) => ((TestClassName)b).CreateDefaultValue());
    public partial int Value {
        get => (int)GetValue(ValueProperty);
        set => SetValue(ValueProperty, value);
    }
}

Tentative PR

• BindableProperty non-static method name enhancement #3002

[TheCodeTraveler]

Hey Stephen! I plan on creating an Analyzer that will generate a compiler error if a developer supplies a method name that is using an invalid method signature.

This analyzer will ensure that developers always use the correct return type and parameter types, and it'll also ensure the method is static, providing a helpful message telling them what's required.

The Analyzer should cover scenarios where a developer forgets to supply a static method to [BindableProperty].

[stephenquan]

Hi Brandon - thanks for the rapid response! An Analyzer would definitely be useful for catching mistakes with the current static method setup. What I'm suggesting, though, is a shift away from requiring static methods altogether. In my proposed generator changes, a static wrapper would handle casting the bindable object to the right type, so developers can just write normal instance methods and let the generator take care of the rest.