Converter Parameter Binding — How to Bind Complex Values at Xamarin(MAUI)

How to resolve Binding for ConverterParameter in Xamarin or MAUI? Short deep dive into reflection in converters 🥹

Sub Folks 🤗, today’s story will be short, but I hope pretty helpfully. All we write or use are some predefined Converters and bind some values. But do you ever try to Bind CommandParameter uh 🧐?

Before we dive deep, let’s refresh how we could bind values to Converter Parameters.

Simple implementation of IValueConverter

Binding a value from BindingContext

Here we bind a object value from our BindingContext, where our Context is our ViewModel. Our Binding is resolved and passes himself object into Converter, which is resolved from Resources as a StaticResource

If you also specify DataType for your Parent Container (like page), you can see hints from your IDE (Visual Studio or Rider) to ensure you don’t make a mistake in your XAML code.

xmlns:viewModels="clr-namespace:ProjectNamespace.ViewModels"
x:DataType="cviewModels:SpecifiedViewModel"

Passing Value from another object in XAML

Also, we able to use some Reference‘s to pass values of runtime available things, for example, some Width of other controls or something from outer contexts, like commands if we are inside a list element with different DataType and BindingContext

Passing simple data into converters

expecting some “double” as a parameter

Nothing extraordinary again, but wait a moment. We will come for more soon 🙃.

Passing static “double” value as Converter Parameter

Same, we can pass some text or static resources, and all of them will be resolved as we expected 😊

Define Boolean Value in XAML and pass StaticResources as Converter Parameter

Passing array of values into Converter

I know, I know, all know it, but if I started, I need to go through them all 😝

Passing Multiple Values(can be diff types or diff ways of passing) into the Converter

And expecting them(values) inside the Converter

And would just like to mention that we may have a list of converters with a list of parameters for each of them 😱

List of Converters with List of Parameters for chaining values through one to another and final Bindable Property.

Xamarin Community Toolkit MultiConverter

Bing Generic things as Converter Parameter 🫣

Here it comes 😁... According to previous examples, we may expect that changing StaticResource to Binding will be resolved by the engine for us. But no, no, no, no, no way it will pass a Binding object 😳

Passing Bindable Value from View Model as Converter Parameter

Binding object is still Binding not value of Binding

Ok, so what we can do and how we can resolve it? — We can check it type, and if it’s Binding and have a Source we can get value from source by Parth by using Reflection.

Updated Converter to check if parameter is a Binding

Special Utils to get value by by using reflection

So, what we are doing here 🤔? We check if propertyName contains any . because that means that we need to resolve property of some property from our Binding Context. Here is why:

Binding Model -> Means that in BindingContext(for example, ViewModel), we have some property named `Model`
Binding Model.InnerModel -> Means that in BindingContext, we have some class or struct property named `Model` which contains public property named `InnerModel` 

That can go with such recursion as deep as it is required. That’s why we check if we contain some inner property by getting the first index of .

If we contain any, we get source (left of the dot) and property name (right of the dot) and recursively calling method GetPropertyValue with updated source and property name. Now we can Bind top-level Properties from our BindingContext and some inner public Properties from more complex objects 😊.

But, if you pay attention inside the converter, we pass Source into GetPropertyValue, and it’s a null somehow, even if we are sure we are under the same BindingContext. To fix that we need specify Source as Reference to parent element or to itself.

Getting Value from Source via BindingContext

Passing ConverterParameter with a Source

Now we may play a little bit with it and bind value with converter and converter parameter, where the converter parameter has bindable value with its own converter and own converter parameter 🤯

Passing simple Converer Parameter into Converter as Converter Parameter 😆

And Resolving step by step value from Binding and then from next Converter

Passing additionally one more inner Binding into Converter Parameter into Binding to Converter Parameter as Binding to Background Color 🤯😱😱😱

I hope after this blog post, you will know that converters may expect slightly more than simple values as Converter Parameter, and you will be ready to resolve all Bindings and inner Converters in your C# code 🙃 😉

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