how to set the width of a column in a datagrid with a multivalue converter?

Question

I would like to set the width of a column in a datagrid according to some conditions, so I wanted to use a multivalue converter.

I am trying this:

<DataGridTextColumn 
                                                Binding="{Binding Modelo}"
                                                Width="*"
                                                CellStyle="{StaticResource ResourceKey=DataGridCellLeftHorizontalAlignment}">

                                <DataGridTextColumn.ElementStyle>
                                    <Style TargetType="{x:Type TextBlock}">
                                        <!--Se pone en blanco por defecto, de este modo si hay líneas de descuento de factura,
                                        no tendrá artículo, es lo correcto.-->
                                        <Setter Property="Width" Value="10"/>
                                        <Setter Property="Width">
                                            <Setter.Value>
                                                <MultiBinding Converter="{StaticResource docListadosDocumentosDataGridComponentesColumnWidthMultiValueConverter}">
                                                    <MultiBinding.Bindings>
                                                        <Binding />
                                                        <Binding ElementName="cmbTiposContenidos" Path="SelectedItem"/>
                                                    </MultiBinding.Bindings>
                                                </MultiBinding>
                                            </Setter.Value>
                                        </Setter>
                                    </Style>
                                </DataGridTextColumn.ElementStyle>

But i don't am not able to set the width with the value that the multivalueconverter returns. The converter, for testing, returns always 500.

How could I set the width of the column with a multivalue converter?

Thanks.

Answer 1

MainWindow.xaml:

<Window.Resources>  
        <local:ViewModel x:Key="vm"/>  
        <local:MyMultiValueConverter x:Key="MyMultiValueConverter"/>  
    </Window.Resources>  
    <StackPanel DataContext="{StaticResource vm}">  
        <DataGrid Name="dg" ItemsSource="{Binding View}" AutoGenerateColumns="False">  
            <DataGrid.Columns>  
                <DataGridTextColumn Header="Col1"  Binding="{Binding SomeString}"  MinWidth="30" MaxWidth="300"  >  
                    <DataGridTextColumn.Width>  
                        <MultiBinding Converter="{StaticResource MyMultiValueConverter}">  
                            <Binding Path="WidthValue" Source="{StaticResource vm}"/>  
                            <Binding Path="WidthDefault" Source="{StaticResource vm}"/>  
                        </MultiBinding>  
                    </DataGridTextColumn.Width>  
                    <DataGridTextColumn.ElementStyle>  
                        <Style TargetType="{x:Type TextBlock}">  
                            <Setter Property="TextAlignment" Value="Center"/>  
                            <Setter Property="Width">  
                                <Setter.Value>  
                                    <MultiBinding Converter="{StaticResource MyMultiValueConverter}">  
                                        <Binding Path="WidthValue" Source="{StaticResource vm}"/>  
                                        <Binding Path="WidthDefault" Source="{StaticResource vm}"/>  
                                    </MultiBinding>  
                                </Setter.Value>  
                            </Setter>  
                        </Style>  
                    </DataGridTextColumn.ElementStyle>  
                </DataGridTextColumn>  
            </DataGrid.Columns>  
        </DataGrid>  
        <CheckBox IsChecked="{Binding WidthDefault}" Content="Default Width"/>  
        <Slider Width="200" Height="20" Minimum="5"  Maximum="300" Value="{Binding WidthValue}"/>  
        <!--<TextBox Text="{Binding WidthValue}"/>-->  
    </StackPanel>  

MainWindow.xaml.cs:

public class ViewModel : INotifyPropertyChanged  
  {  
    public ViewModel()  
    {  
      ObservableCollection<Data> col = new ObservableCollection<Data>();  
       col.Add(new Data() { SomeString = 44 });  
       col.Add(new Data() { SomeString = 84 });  
       col.Add(new Data() { SomeString = 104 });  
      cvs.Source = col;  
    }  
    private CollectionViewSource cvs = new CollectionViewSource();  
    public ICollectionView View { get => cvs.View; }  
  
    private double _widthValue = 30;  
    public double WidthValue  
    {  
      get => this._widthValue;  
      set { this._widthValue = value; OnPorpertyChanged(); }  
    }  
  
    private bool _widthDefault = false;  
    public bool WidthDefault  
    {  
      get => this._widthDefault;  
      set { this._widthDefault = value; OnPorpertyChanged(); }  
    }  
  
    public event PropertyChangedEventHandler PropertyChanged;  
    internal void OnPorpertyChanged([CallerMemberName] string propName = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));  
  
  }  
  
  public class Data  
  {  
    public double SomeString { get; set; }  
  }  
  
  public class MyMultiValueConverter : IMultiValueConverter  
  {  
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)  
    {  
      double w =30;  
      if (!(bool)values[1]) double.TryParse(values[0].ToString(), out w);  
      return w;  
    }  
    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)  
    {  
      throw new NotImplementedException();  
    }  
  }  

The result:

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Answer 2

The solution it is to use 2 converters, one for the width of the column and the other for the width of the textblock, because for the column it is needed to use a DataGridLength:

The solution would be this:

The view model:

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows.Data;
using System.Runtime.CompilerServices;
using System.Globalization;
using System.Windows.Controls;

namespace ModificarColumnaDataGridConMultivalueConverter
{
    public class ViewModel : INotifyPropertyChanged
    {
        public ViewModel()
        {
            ObservableCollection<Data> col = new ObservableCollection<Data>();
            col.Add(new Data() { SomeString = 44 });
            col.Add(new Data() { SomeString = 84 });
            col.Add(new Data() { SomeString = 104 });
            cvs.Source = col;
        }
        private CollectionViewSource cvs = new CollectionViewSource();
        public ICollectionView View { get => cvs.View; }

        private double _widthValue = 30;
        public double WidthValue
        {
            get => this._widthValue;
            set { this._widthValue = value; OnPorpertyChanged(); }
        }

        private bool _widthDefault = false;
        public bool WidthDefault
        {
            get => this._widthDefault;
            set { this._widthDefault = value; OnPorpertyChanged(); }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        internal void OnPorpertyChanged([CallerMemberName] string propName = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
    }


    public class Data
    {
        public double SomeString { get; set; }
    }

    public class MyColumnWidthConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            double w = 30;
            if (!(bool)values[1]) double.TryParse(values[0].ToString(), out w);
            return new DataGridLength(w);
        }
        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

    public class MyTexBlockWidthConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            double w = 30;
            if (!(bool)values[1]) double.TryParse(values[0].ToString(), out w);
            return w;
        }
        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

And the view:

<Window x:Class="ModificarColumnaDataGridConMultivalueConverter.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:ModificarColumnaDataGridConMultivalueConverter"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">


    <Window.Resources>
        <local:ViewModel x:Key="vm"/>
        <local:MyColumnWidthConverter x:Key="MyColumnWidthConverter"/>
        <local:MyTexBlockWidthConverter x:Key="MyTexBlockWidthConverter"/>
    </Window.Resources>
    <StackPanel DataContext="{StaticResource vm}">
        <DataGrid Name="dg" ItemsSource="{Binding View}" AutoGenerateColumns="False">
            <DataGrid.Columns>
                <DataGridTextColumn Header="Col1"  Binding="{Binding SomeString}"  MinWidth="0" MaxWidth="300"  >
                    <DataGridTextColumn.Width>
                        <MultiBinding Converter="{StaticResource MyColumnWidthConverter}">
                            <Binding Path="WidthValue" Source="{StaticResource vm}"/>
                            <Binding Path="WidthDefault" Source="{StaticResource vm}"/>
                        </MultiBinding>
                    </DataGridTextColumn.Width>
                    <DataGridTextColumn.ElementStyle>
                        <Style TargetType="{x:Type TextBlock}">
                            <Setter Property="TextAlignment" Value="Center"/>
                            <Setter Property="Width">
                                <Setter.Value>
                                    <MultiBinding Converter="{StaticResource MyTexBlockWidthConverter}">
                                        <Binding Path="WidthValue" Source="{StaticResource vm}"/>
                                        <Binding Path="WidthDefault" Source="{StaticResource vm}"/>
                                    </MultiBinding>
                                </Setter.Value>
                            </Setter>
                        </Style>
                    </DataGridTextColumn.ElementStyle>
                </DataGridTextColumn>
            </DataGrid.Columns>
        </DataGrid>
        <CheckBox IsChecked="{Binding WidthDefault}" Content="Default Width"/>
        <Slider Width="200" Height="20" Minimum="5"  Maximum="300" Value="{Binding WidthValue}"/>
        <!--<TextBox Text="{Binding WidthValue}"/>-->
    </StackPanel>
</Window>