Databinding into grid's columnDefinition width

Trixo · July 2019

Hi, I am having problems with binding into grid's columndefinition width proprety.
I tried TestWidth.Value as well as just double and string.
Any idea whats the problem?

`<ColumnDefinition Width="{Binding Parent.SizeModifier.TestWidth, Source={x:Reference Self}}"></ColumnDefinition>`

    class SizeModifier
    {
        public int DefaultWindowWidth { get; set; }
        public int DefaultWindowHeight { get; set; }
        public int DefaultWindowDPI { get; set; }
        public double WidthModifier { get; set; }
        public double HeightModifier { get; set; }
        public double DPIModifier { get; set; }
        public int DeviceWidth { get; set; }
        public int DeviceHeight { get; set; }
        public int DeviceDPI { get; set; }
        public GridLength TestWidth { get; set; }
        public string Test = "400";

        public SizeModifier()
        {
            DefaultWindowWidth = 1280;
            DefaultWindowHeight = 800;
            DefaultWindowDPI = 160;
            DeviceDPI = DependencyService.Get<IGetScreenSizes>().GetDisplayDpi();
            DeviceWidth = DependencyService.Get<IGetScreenSizes>().GetDisplayWidth();
            DeviceHeight = DependencyService.Get<IGetScreenSizes>().GetDisplayHeight();
            DPIModifier = (double)DeviceDPI / (double)DefaultWindowDPI;
            WidthModifier = (double)DeviceWidth / (double)DefaultWindowWidth*DPIModifier;
            HeightModifier = (double)DeviceHeight / (double)DefaultWindowHeight*DPIModifier;
            TestWidth = new GridLength((double)400 * WidthModifier, GridUnitType.Absolute);

        }
    }


}

Amar_Bait · July 2019

Binding requires a declared static BindableProperty (that has the same name as the backing property plus "Property" suffix)

public static BindableProperty TestWidth**Property** = BindableProperty.Create(nameof(TestWidth), typeof(GridLength), typeof(SizeModifier), defaultValue: GridLength.Star);

public GridLength TestWidth 
{
    get =>(GridLength)GetValue(TestWidthProperty);
    set => SetValue(TestWidthProperty, value);
}

Trixo · July 2019

@Amar_Bait This is not a problem. I have used same structure to bind the values. Everything else works, but SizeModifier.

app.xaml.cs
 ApplicationBindings ApplicationBind { get; set; }

applicationBindings
    class ApplicationBindings
    {
        public Navigation AppNavigation { get; set; }
        public Battery BatteryStatus { get; set; }
        public UserData UserData { get; set; }
        public DeviceData DeviceData { get; set; }
        public VitalsData VitalsData { get; set; }
        public SizeModifier SizeModifier { get; set; }
    }

Trixo · July 2019

In boxview's widthrequest following works.
{TemplateBinding Parent.BindingContext.SizeModifier.TestWidth.Value}

I am not able to use it in columndefinition's width because of https://github.com/xamarin/Xamarin.Forms/issues/4835

Trixo · July 2019

Following works.
{Binding BindingContext.SizeModifier.TestWidth, Source={x:Reference Self}}

seems like no need for Parent keyword.

Alex0407 · April 2020

Dears

I have more or less the same issue. I am working on some template control currently. It uses Grid to place two labels.

the code behind is the following

    public static readonly BindableProperty PromptWidthProperty = BindableProperty.Create(
                                            nameof(PromptWidth),
                                            typeof(GridLength),
                                            typeof(TextFieldViewControl),
                                            defaultValue: GridLength.Star);

    public GridLength PromptWidth
    {
        get
        {
            return (GridLength)GetValue(PromptWidthProperty);
        }
        set
        {
            SetValue(PromptWidthProperty, value);
        }
    }

XAML code

<ContentView.ControlTemplate>
    <ControlTemplate>

        <Grid Margin="0,0,0,12" 
                BackgroundColor="{TemplateBinding BackgroundColor}">

            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="{TemplateBinding PromptWidth}"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>

.....

The following exception is thrown as soon as I enable TemplateBinding for column width. The control works fine without it.
What can be the issue ?

Exception has been thrown by the target of an invocation.

Thank you in advance

Trixo · April 2020

@Alex0407 Have you tried my solution?
Set parent container's xname to x:Name="Self

and then just use normal binding with source reference to that element

{Binding BindingContext.SizeModifier.TestWidth, Source={x:Reference Self}}

Alex0407 · April 2020

Hi Trixo

thank you for your fast feedback.
I have updated the solution accordingly to your recommendations and it works.

it was before
ColumnDefinition Width="{TemplateBinding PromptWidth}"

it is now
ColumnDefinition Width="{Binding PromptWidth, Source={x:Reference this}}"

where "this" is declared as below
x:Name="this"

If TemplateBinding is used then the following exception is thrown

System.InvalidOperationException: 'Operation is not valid due to the current state of the object.'

Why does TemplateBinding work fine for other bindable properties of the same control ?

For example, the control has a property declared like this
<Label Grid.Column="0" Grid.Row="0"
Text="{TemplateBinding PromptText}"
Style="{StaticResource TextFieldViewPrompt}"

and it works fine always.

What is the possible reason of such difference ? Data type ?

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