[ACCEPTED]-WPF binding with StringFormat doesn't work on ToolTips-binding

ToolTips in WPF can contain anything, not 8 just text, so they provide a ContentStringFormat 7 property for the times you just want text. You'll 6 need to use the expanded syntax as far as 5 I know:

<TextBox ...>
  <TextBox.ToolTip>
    <ToolTip 
      Content="{Binding ElementName=myTextBlock,Path=Text}"
      ContentStringFormat="{}It is: {0}"
      />
  </TextBox.ToolTip>
</TextBox>

I'm not 100% sure about the validity 4 of binding using the ElementName syntax 3 from a nested property like that, but the 2 ContentStringFormat property is what you're 1 looking for.

It could be a bug. When you use short syntax 2 for tooltip:

<TextBox ToolTip="{Binding WhatEverYouWant StringFormat='It is: \{0\}'}" />

StringFormat is ignore but when 1 you use expanded syntax:

<TextBox Text="text">
   <TextBox.ToolTip>
      <TextBlock Text="{Binding WhatEverYouWant StringFormat='It is: \{0\}'}"/>
   </TextBox.ToolTip>
</TextBox>

It works as expected.

As Matt said ToolTip can contain anything 4 inside so for your you could bind a TextBox.Text 3 inside your ToolTip.

<StackPanel>
    <TextBlock x:Name="MyTextBlock">Foo Bar</TextBlock>
    <TextBox Text="{Binding ElementName=MyTextBlock, Path=Text, StringFormat='It is: \{0\}'}">
        <TextBox.ToolTip>
            <TextBlock>
                <TextBlock.Text>
                    <Binding ElementName=MyTextBlock Path="Text" StringFormat="It is: {0}" />
                </TextBlock.Text>
            </TextBlock>
        </TextBox.ToolTip>
    </TextBox>
</StackPanel>

Even you can Stack a 2 grid inside the ToolTip and layout your 1 text if you want.

Your code can be as short as this:

<TextBlock ToolTip="{Binding PrideLands.YearsTillSimbaReturns,
    Converter={StaticResource convStringFormat},
    ConverterParameter='Rejoice! Just {0} years left!'}" Text="Hakuna Matata"/>

We'll 3 use the fact Converters are never ignored, unlike 2 StringFormat.

Put this into StringFormatConverter.cs:

using System;
using System.Globalization;
using System.Windows;
using System.Windows.Data;

namespace TLKiaWOL
{
    [ValueConversion (typeof(object), typeof(string))]
    public class StringFormatConverter : IValueConverter
    {
        public object Convert (object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (ReferenceEquals(value, DependencyProperty.UnsetValue))
                return DependencyProperty.UnsetValue;
            return string.Format(culture, (string)parameter, value);
        }

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

Put this into 1 your ResourceDictionary.xaml:

<conv:StringFormatConverter x:Key="convStringFormat"/>

In this situation, you can use relative 1 binding:

<StackPanel>
    <TextBlock x:Name="MyTextBlock">Foo Bar</TextBlock>
    <TextBox Text="{Binding ElementName=MyTextBlock, Path=Text, StringFormat='It is: \{0\}'}"
             ToolTip="{Binding Text, RelativeSource={RelativeSource Self}}" />
</StackPanel>