How to set a top margin only in XAML?

I can set margins individually in code but how do I do it in XAML, e.g. how do I do this:

PSEUDO-CODE:

<StackPanel Margin.Top="{Binding TopMargin}">

Isn't this what you're looking for?

<StackPanel Margin="0,10,0,0" />

The first value is Left margin, then Top, then Right, and last but not least Bottom.

I'm not sure if you want to bind it to something, but if not, that'll work.

The key is to realize that setting it in code like this:

sp2.Margin = new System.Windows.Thickness{ Left = 5 };

is equivalent to:

sp2.Margin = new System.Windows.Thickness{ Left = 5, Top = 0, Right = 0, Bottom = 0 };

You can't set just a single value in a Thickness instance through either code or XAML. If you don't set some of the values, they will be implicitly zero. Therefore, you can just do this to convert the accepted code sample in your other question to a XAML equivalent:

<StackPanel Margin="{Binding TopMargin, Converter={StaticResource MyConverter}}"/>

where MyConverter just returns a Thickness that sets only the Top and leaves all other values as zero.

Of course, you could write your own control that does expose these individual values as dependency properties to make your code a little cleaner:

<CustomBorder TopMargin="{Binding TopMargin}">
</CustomBorder>

A better option than a custom control would be to write an attached property and change the Thickness using the code above in the dependency property setter. The below code would be usable across ALL controls which have a Margin.

public static readonly DependencyProperty TopMarginProperty =
    DependencyProperty.RegisterAttached("TopMargin", typeof(int), typeof(FrameworkElement),
                                        new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender));
public static void SetTopMargin(FrameworkElement element, int value)
{
    // set top margin in element.Margin
}
public static int GetTopMargin(FrameworkElement element)
{
    // get top margin from element.Margin
}

If you couple this with a Behavior, you can get notification changes on the TopMargin property.

This belongs to the WPF/XAML commandments:

1. I am WPF/XAML, thy UI framework, and you will use me when coding apps for Windows - eventually.
2. Thou shalt have no other technologies - I will not be cross-platform but I'll try to with Silverlight UWP, because Hololens is going to be huge some day. _{"Xamarin.Forms"? Never heard of it!}
3. Thou shalt inevitably take the name of the Lord in vain, repeatedly, when using WPF/XAML.
4. Remember the sabbath day: every 7 days... or hours or minutes of coding I will make you take a break to go to StackOverflow and 2000things.
5. Honor thy father and mother: Windows Forms.
6. Should thou shalt adopt MVVM, thou shalt also implement INPC and INCC, but rejoice! Thou hast a choice: you can use it or you can use it with anger.
7. Thou shalt not commit adultery interop with other apps and frameworks.
8. Thou shalt not covet thy neighbour's UI framework.
9. Thou shalt not be able to set a position of an element dynamically using binding of an either attached property or margin without writing few lines of code-behind.
10. Thou shalt never have a simple bool Visibility property in XAML. I am WPF/XAML.

Your sin is listed at #9.

Just wrote some attached properties that should make it easy to set an individual Margin value from a binding or static resource:

public class Margin
{
    public static readonly DependencyProperty LeftProperty = DependencyProperty.RegisterAttached(
        "Left",
        typeof(double),
        typeof(Margin),
        new PropertyMetadata(0.0));

    public static void SetLeft(UIElement element, double value)
    {
        var frameworkElement = element as FrameworkElement;
        if (frameworkElement != null)
        {
            Thickness currentMargin = frameworkElement.Margin;

            frameworkElement.Margin = new Thickness(value, currentMargin.Top, currentMargin.Right, currentMargin.Bottom);
        }
    }

    public static double GetLeft(UIElement element)
    {
        return 0;
    }

    public static readonly DependencyProperty TopProperty = DependencyProperty.RegisterAttached(
        "Top",
        typeof(double),
        typeof(Margin),
        new PropertyMetadata(0.0));

    public static void SetTop(UIElement element, double value)
    {
        var frameworkElement = element as FrameworkElement;
        if (frameworkElement != null)
        {
            Thickness currentMargin = frameworkElement.Margin;

            frameworkElement.Margin = new Thickness(currentMargin.Left, value, currentMargin.Right, currentMargin.Bottom);
        }
    }

    public static double GetTop(UIElement element)
    {
        return 0;
    }

    public static readonly DependencyProperty RightProperty = DependencyProperty.RegisterAttached(
        "Right",
        typeof(double),
        typeof(Margin),
        new PropertyMetadata(0.0));

    public static void SetRight(UIElement element, double value)
    {
        var frameworkElement = element as FrameworkElement;
        if (frameworkElement != null)
        {
            Thickness currentMargin = frameworkElement.Margin;

            frameworkElement.Margin = new Thickness(currentMargin.Left, currentMargin.Top, value, currentMargin.Bottom);
        }
    }

    public static double GetRight(UIElement element)
    {
        return 0;
    }

    public static readonly DependencyProperty BottomProperty = DependencyProperty.RegisterAttached(
        "Bottom",
        typeof(double),
        typeof(Margin),
        new PropertyMetadata(0.0));

    public static void SetBottom(UIElement element, double value)
    {
        var frameworkElement = element as FrameworkElement;
        if (frameworkElement != null)
        {
            Thickness currentMargin = frameworkElement.Margin;

            frameworkElement.Margin = new Thickness(currentMargin.Left, currentMargin.Top, currentMargin.Right, value);
        }
    }

    public static double GetBottom(UIElement element)
    {
        return 0;
    }
}

Usage:

<TextBlock Text="Test"
    app:Margin.Top="{Binding MyValue}"
    app:Margin.Right="{StaticResource MyResource}"
    app:Margin.Bottom="20" />

Tested in UWP but this should work for any XAML-based framework. The nice thing is they won't override the other values on the Margin, so you can combine them as well.

You can't define just the Top margin with a binding, because Margin is of type Thickness which isn't a dependency object. However you could use a MultiValueConverter that would take 4 margin values to make 1 Thickness objects

Converter :

public class ThicknessMultiConverter : IMultiValueConverter
{
    #region IMultiValueConverter Members

    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        double left = System.Convert.ToDouble(values[0]);
        double top = System.Convert.ToDouble(values[1]);
        double right = System.Convert.ToDouble(values[2]);
        double bottom = System.Convert.ToDouble(values[3]);
        return new Thickness(left, top, right, bottom);
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        Thickness thickness = (Thickness)value;
        return new object[]
        {
            thickness.Left,
            thickness.Top,
            thickness.Right,
            thickness.Bottom
        };
    }

    #endregion
}

XAML :

<StackPanel>
    <StackPanel.Margin>
        <MultiBinding Converter="{StaticResource myThicknessConverter}">
            <Binding Path="LeftMargin"/>
            <Binding Path="TopMargin"/>
            <Binding Path="RightMargin"/>
            <Binding Path="BottomMargin"/>
        </MultiBinding>
    </StackPanel.Margin>
</StackPanel>

Here's a simple way of doing this without writing converters or hard-coding margin values. First, define the following in your Window (or other control) resources:

<Window.Resources>
    <!-- Define the default amount of space -->
    <system:Double x:Key="Space">10.0</system:Double>

    <!-- Border space around a control -->
    <Thickness
        x:Key="BorderSpace"
        Left="{StaticResource Space}"
        Top="{StaticResource Space}"
        Right="{StaticResource Space}"
        Bottom="{StaticResource Space}"
        />

    <!-- Space between controls that are positioned vertically -->
    <Thickness
        x:Key="TopSpace"
        Top="{StaticResource Space}"
        />
</Window.Resources>

Note that system is defined as xmlns:system="clr-namespace:System;assembly=mscorlib".

Now you can use these resources as follows:

<Grid
    Margin="{StaticResource BorderSpace}"
    >
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>

    <Button
        Grid.Row="0"
        Content="Button 1"
        />

    <Button
        Grid.Row="1"
        Content="Button 2"
        Margin="{StaticResource TopSpace}"
        />
</Grid>

Now if you want to change the default space between controls, you only need to change it in one place.

Use a converter, the sample code below will convert the double you are binding to to a thickness. It will set the "Top" of the thickness to the bound field. You could optionally use a ConverterParameter to determine if you are binding to left, top, right, or bottom.

<StackPanel Margin="{Binding TopMargin, Converter={StaticResource MyThicknessConverter}">

.

public class ThicknessSingleValueConverter : IValueConverter
{
    override Convert(...)
    {
         return new Thickness(0, (double)object, 0, 0);
    }
  
    //etc...

I thought You could use the property syntax, from MSDN:

      <object.Margin>
        <Thickness Top="{Binding Top}"/>
      </object.Margin>

Than you won't need any converter

But the Top is not DependancyProperty - back to converter

Here's a nifty solution:

        public class Nifty
    {
        private static double _tiny;
        private static double _small;
        private static double _medium;
        private static double _large;
        private static double _huge;
        private static bool _resourcesLoaded;

        #region Margins

        public static readonly DependencyProperty MarginProperty =
            DependencyProperty.RegisterAttached("Margin", typeof(string), typeof(Nifty),
                new PropertyMetadata(string.Empty,
                    new PropertyChangedCallback(OnMarginChanged)));

        public static Control GetMargin(DependencyObject d)
        {
            return (Control)d.GetValue(MarginProperty);
        }

        public static void SetMargin(DependencyObject d, string value)
        {
            d.SetValue(MarginProperty, value);
        }

        private static void OnMarginChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            FrameworkElement ctrl = d as FrameworkElement;
            if (ctrl == null)
                return;

            string Margin = (string)d.GetValue(MarginProperty);

            ctrl.Margin = ConvertToThickness(Margin);
        }

        private static Thickness ConvertToThickness(string Margin)
        {
            var result = new Thickness();

            if (!_resourcesLoaded)
            {
                _tiny = (double)Application.Current.FindResource("TinySpace");
                _small = (double)Application.Current.FindResource("SmallSpace");
                _medium = (double)Application.Current.FindResource("MediumSpace");
                _large = (double)Application.Current.FindResource("LargeSpace");
                _huge = (double)Application.Current.FindResource("HugeSpace");

                _resourcesLoaded = true;
            }

            result.Left = CharToThickness(Margin[0]);
            result.Top = CharToThickness(Margin[1]);
            result.Bottom = CharToThickness(Margin[2]);
            result.Right = CharToThickness(Margin[3]);

            return result;
        }


        private static double CharToThickness(char p)
        {
            switch (p)
            {
                case 't':
                case 'T':
                    return _tiny;
                case 's':
                case 'S':
                    return _small;
                case 'm':
                case 'M':
                    return _medium;
                case 'l':
                case 'L':
                    return _large;
                case 'h':
                case 'H':
                    return _huge;
                default:
                    return 0.0;
            }
        }

        #endregion

    }

If you add this code to your namespace and define the following sizes:

	<system:Double x:Key="TinySpace">2</system:Double>
<system:Double x:Key="SmallSpace">5</system:Double>
<system:Double x:Key="MediumSpace">10</system:Double>
<system:Double x:Key="LargeSpace">20</system:Double>
<system:Double x:Key="HugeSpace">20</system:Double>

You can then create Tiny, Small, Medium, Large & Huge margins like this:

local:Nifty.Margin="H000"

or

local:Nifty.Margin="_S_S"

The code will then create margins based on your resources.

Maybe I am "late to the party", but didn't like any of provided solutions, and it seems to me that simplest and cleanest solution is define Thickness property in ViewModel (or anything that you are binding) and then Bind that property. Something like this:

public class ItemViewModel
{
  public Thickness Margin { get; private set }

  public ItemViewModel(ModelClass model)
  {
    /// You can calculate needed margin here, 
    /// probably depending on some value from the Model
    this.Margin = new Thickness(0,model.TopMargin,0,0);
  }
}

And then XAML is simple:

<StackPanel Margin="{Binding Margin}">

I use a ValueConverter bound to Margin (RelativeSource Self) and Parse the ConverterParameter, given as "top:123;left:456".

The Converter only overwrites Margins given by Parameter.

public class MarginConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (!(value is Thickness)) return new Thickness();

        Thickness retMargin = (Thickness) value;
        List<string> singleMargins = (parameter as string)?.Split(';').ToList() ?? new List<string>();

        singleMargins.ForEach(m => {
                                  switch (m.Split(':').ToList()[0].ToLower().Trim()) {
                                      case "left":
                                          retMargin.Left = double.Parse(m.Split(':').ToList()[1].Trim());
                                          break;
                                      case "top":
                                          retMargin.Top = double.Parse(m.Split(':').ToList()[1].Trim());
                                          break;
                                      case "right":
                                          retMargin.Right = double.Parse(m.Split(':').ToList()[1].Trim());
                                          break;
                                      case "bottom":
                                          retMargin.Bottom = double.Parse(m.Split(':').ToList()[1].Trim());
                                          break;
                                  }
                              }
            );
        return retMargin;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

xaml

<TextBlock Margin="{Binding RelativeSource={RelativeSource Self}, 
                    Path=Margin, 
                    Converter={StaticResource MarginConverter}, 
                    ConverterParameter='top:0'}" 
Style="{StaticResource Header}" 
Text="My Header" />

TextBlock would use the Margin given by Style except the Margin-Top, that will be overwritten with 0.

Have fun with it!

What would be nice is to be able to do this by specifying something like the code example below.

<StackPanel Margin=",10,,">

Unfortunately this capability doesn't seem to exist by default in WPF and it's a shame because it requires developers to hard code known default values in a way that later makes it more difficult to skin or theme an application.

The best solution that I can think of at this point is using a converter, but the amount of extra code you have to produce to introduce this is not ideal.