ImageResourceConverter - Binding could be compiled to improve runtime performance if x:DataType is not explicitly null.

[LeoJHarris]

Hi All,

I have enabled the following in my csproj, that is to take advantage of compiled bindings

<MauiEnableXamlCBindingWithSourceCompilation>true</MauiEnableXamlCBindingWithSourceCompilation>
<WarningsAsErrors>$(WarningsAsErrors);XC0022;XC0023</WarningsAsErrors>

When I use the following I get an error that the binding could be compiled to improve runtime performance which I expect but I cannot seem to get past the error

<Image
    Grid.Column="0"
    x:DataType="{x:Null}"
    Aspect="AspectFit"
    HeightRequest="24"
    Source="{Binding Source={StaticResource ConversationImageSource}, Converter={StaticResource ImageResourceConverter}}"
    VerticalOptions="Center"
    WidthRequest="24" />

If I disable/remove the WarningsAsErrors then the x:DataType="{x:Null}" doesn't cause the build error and the image displays but then I lose the benefit of potentially using compiled binding.

Is it possible to use compiled binding in this case so I can keep the WarningsAsErrors enabled?

[bijington]

Why are you setting x:DataType="{x:Null}"? Why can't you specify an actual type for the DataType?

[LeoJHarris]

@bijington sorry revising this, are you able to advise the DataType when enabling MauiEnableXamlCBindingWithSourceCompilation in combination with using ImageResourceConverter? I cannot get the image to show and not sure what the binding context should be in type of scenario?

[stephenquan]

Can you supply a copy of your ResourceDictionary including the ConversationImageSource definition?

[LeoJHarris]

@stephenquan

The ConversationImageSource is like the follows defined in Styles.xaml from directory Resources => Styles => Prod

<?xml version="1.0" encoding="UTF-8" ?>
<ResourceDictionary
    x:Class="SampleApp.Resources.Styles.Prod.Styles"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:customviews="clr-namespace:SampleApp.CustomViews"
    xmlns:tabs="http://sharpnado.com">
<x:String x:Key="ConversationImageSource">SampleApp.Resources.Images.Prod.logo.png</x:String>

The entire .xaml file is merged into App.xaml like the follows

App.xaml

<Application.Resources>
    <ResourceDictionary x:Name="AppDictionary">
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="Resources/Styles/Styles.xaml" />

Including the following when the app launches.

switch (lazyBuildConfigService.Value.GetBuildCustomer())
{
    case BuildCustomer.Prod:
        loadStyles(BuildCustomer.Prod);
        break;
}

private void loadStyles(BuildCustomer buildFlavor)
{
    switch (buildFlavor)
    {
        case BuildCustomer.Prod:
            AppDictionary.MergedDictionaries.Add(new Resources.Styles.Prod.Colors());
            AppDictionary.MergedDictionaries.Add(new Resources.Styles.Prod.Styles());
            break;

We actually have multiple Styles.xaml nested in certain directories beneath Resources folder and depending on the BuildCustomer we use that Style & Color .xaml files.

[LeoJHarris]

in case anyone stumbles on this, the solution ended up quite simple :DataType=x:String as suggested here dotnet/maui#27292 (reply in thread)

 Source="{Binding Source={StaticResource LogoVariant2ImageSource}, Converter={StaticResource ImageResourceConverter}, x:DataType=x:String}"

[stephenquan]

Setting x:DataType is the key. It won't always be x:String. In this case we observe Source={StaticResource ConversationImageSource} and when we check the ResourceDictionary we see that ConversationImageSource is an x:String this is why you need to set x:DataType=x:String.