c#mauimaui-community-toolkitmaui-markup-community-toolkit
Nested Binding Examples in
How to use complex / nested bindings with TypedBinding in .NET MAUI C# Markup?
I'm using TypedBindings in CommunityToolkit.Maui.Markup and my binding is not working as expected when binding to a property nested inside of another property.
In the sample code below, the Label text is updated using the "old" binding method that uses Reflection:
.Bind(Label.TextProperty, path: "NestedObject.Test")
but the Label text does not get updated when using TypedBindings (no reflection):
.Bind(Label.TextProperty,
static (TestModel myModel) => myModel.NestedObject.Test)
Code
class TestView : ContentPage
{
TestModel model;
public TestView()
{
model = new TestModel();
BindingContext = model;
Content = new Grid
{
Children =
{
new VerticalStackLayout
{
new Label
{
}.Bind(Label.TextProperty, path: "NestedObject.Test"),
new Label
{
}.Bind(Label.TextProperty,
static (TestModel myModel) => myModel.NestedObject.Test,
new Entry
{
}.Bind(Entry.TextProperty,
static (TestModel model) => model.NestedObject.Test
static (TestModel model, string value) => model.NestedObject.Test = value),
}
}
};
}
}
partial class TestModel : ObservableObject
{
[ObservableProperty]
NestedObject nestedObject = new();
[ObservableProperty]
NestedObject? nestedObject2;
[ObservableProperty]
string title = "My Title";
}
partial class NestedObject : ObservableObject
{
[ObservableProperty]
string test = "Initial";
}
Solution
For TypedBindings, a nested binding requires you to include the handlers parameter.
It looks like you're just missing the handlers parameter. Below is the updated code as well as a GIF of the working sample app.
I've also submitted a PR here adding the handlers to demonstrate the missing code: https://github.com/Falco94/CommunityToolkit.IssueTest/pull/1
Updated Sample Code
public class TestView : ContentPage
{
TestModel model;
public TestView()
{
model = new TestModel();
BindingContext = model;
Content = new Grid
{
Children =
{
new VerticalStackLayout
{
new Label
{
}.Bind(Label.TextProperty, path: "NestedObject.Test"),
new Label
{
}.Bind(Label.TextProperty,
getter: static (TestModel myModel) => myModel.NestedObject.Test,
handlers: new (Func<TestModel, object?>, string)[]
{
(vm => vm, nameof(TestModel.NestedObject)),
(vm => vm.NestedObject, nameof(TestModel.NestedObject.Test)),
}),
new Entry
{
}.Bind(Entry.TextProperty,
getter: static (TestModel model) => model.NestedObject.Test,
handlers: new (Func<TestModel, object?>, string)[]
{
(vm => vm, nameof(TestModel.NestedObject)),
(vm => vm.NestedObject, nameof(TestModel.NestedObject.Test)),
},
setter: (TestModel model, string value) => model.NestedObject.Test = value),
}
}
};
}
}