Tag Archives: markup

Introduction to Multi Binding and Multi value converter using IMultiValueConverter & MultiBinding

For Introduction to Value Converters, see the post here.

For more information on mode property, see the the post on mode here.

MultiBinding allows us to bind a binding target property to a list of source properties and then apply logic to produce a value with the given inputs. This example demonstrates how to use MultiBinding. The following example produces a TextBox that adds the numbers in TextBox1 and TextBox2 and puts the result into TextBox3. Here we have two source properties and the one target property. When you enter numbers in the TextBox1 and TextBox2 , the converter comes into play and automatically adds them and puts the result into TextBox3. The values of the Mode and UpdateSourceTrigger properties determine the functionality of the MultiBinding and are used as the default values for all the bindings in the collection unless an individual binding overrides these properties. For example, if the Mode property on the MultiBinding object is set to TwoWay, then all the bindings in the collection are considered TwoWay unless you set a different Mode value on one of the bindings explicitly.

In the following code, AddConverter implements the IMultiValueConverter interface. AddConverter takes the values from the individual bindings and stores them in the values object array. The order in which the Binding elements appear under the MultiBinding element is the order in which those values are stored in the array.

 

Figure1: Important Classes hierarchy.

Figure2: Binding classes hierarchy

The XAML for the above mentioned logic is as follows.

<Window x:Class="DataConversion.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation&quot;
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml&quot;
        Title="MainWindow" Height="350" Width="525"
        xmlns:mylocalXAMLnamespace="clr-namespace:DataConversion">
    <StackPanel>
        <StackPanel.Resources>
            <mylocalXAMLnamespace:AddConverter x:Key="XAMLResourceAddConverter" />
        </StackPanel.Resources>

        <TextBox Name="TextBox1" Text="10"></TextBox>
        <TextBox Name="TextBox2" Text="20"></TextBox>
        <Label Content="Sum of above two values:"></Label>
        <TextBox Name="textBox3">
            <TextBox.Text>
                <MultiBinding Converter="{StaticResource XAMLResourceAddConverter}">
                    <Binding ElementName="TextBox1" Path="Text"/>
                    <Binding ElementName="TextBox2" Path="Text"/>
                </MultiBinding>
            </TextBox.Text>
        </TextBox>
    </StackPanel>
</Window>

 

The MultiBinding tag takes binding as a parameter. See the following C# code that does the binding.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Markup;

namespace DataConversion
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

    }

    public class AddConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            int result = Int32.Parse((string)values[0]) + Int32.Parse((string)values[1]);
            return result.ToString();
        }
        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotSupportedException("Cannot convert back");
        }
    }

}

 

You can specify multiple bindings in a MultiBinding object. When you use the MultiBinding object with a converter, it produces a final value for the binding target based on the values of those bindings. For example, color might be computed from red, blue, and green values, which can be values from the same or different binding source objects. When a value moves from the target to the sources, the target property value is translated to a set of values that are fed back into the bindings.

Download the Source Code from here

If it’s a good idea, go ahead and do it. It is much easier to apologize than it is to get permission. Admiral Grace Hopper

Data Binding–Source & Target

WPF Data Binding:

In data binding we establish a connection between the properties of two objects that are interested in binding. Binding means establishing a relationship or forming a bond between two entities. In this relationship, one object is referred to as the source and one object is referred to as the target. In the most typical scenario, your source object is the object that contains your data and your target object is a control that displays that data.

For instance, consider a Employee class with a EmployeeName property. If you want to show the EmployeeName property value in the TextBox UI and have the UI automatically change when the EmployeeName property value changes at run-time, you can bind the TextBox.Text property to the EmployeeName property of the Employee object as shown in the following figure 1.

image    Figure 1: Source & Target Objects in Binding

Download code from my article here.

ABCs of Data Binding

Building the presentation (User Interface) applications is all about displaying and manipulation of data. Well, WPF has a powerful feature to display data in UI controls that can be bound to the data present in our control (business) or entity (data) classes or any class data for that matter.

Suppose you have a class called person and it has a property  public string PersonName that you want to display in a text box. How do we bind these two objects together? Well, WPF’s DataBinding comes to the rescue. Each binding has these four components:

  • A binding target object
  • A target property
  • A binding source
  • A path to the value in the binding source to use.

For example,if you want to bind the content of a TextBox to the Name property of an employee object, your target object is the TextBox, the target property is the Text property, the value to use is EmployeeName, and the source object is the employee object. The following figure illustrates the concepts of DataBinding.

 

image

Figure 1: Components of DataBinding

Mode Property:

You use the Mode property to specify the direction of the binding, i.e. source -> target or target <- source. The following enumeration list shows the available options for binding

  • Default causes the default Mode value of target property to be used.
  • OneTime updates the target property only when the application starts or when the DataContext undergoes a change.
  • OneWay updates the target property only when the source property changes.
  • TwoWay updates the target property or the property whenever either the target property or the source property changes.
  • OneWayToSource updates the source property when the target property changes.

UpdateSourceTrigger Property:

The UpdateSourceTrigger property of the binding determines what triggers the update of the source. If you a bind a variable to a control, then the data from the control can be transferred to the variable by using this property.

  • Default: Any of the following values (Depends on the control)
  • Explicit:The Source Value Gets Updated when the appications calls UpdateSource
  • LostFocus: The Source Value Gets Updated when the UIElement control loses focus
  • PropertyChanged:The Source Value Gets Updated when the user types in the UIElement control

Following is the code of the employee class that exposes a property called EmployeeName that we want to bind to the textbox control. To make binding happen, the following should be implemented on the data class.

  1. Derive the class exposing the properties from INotifyPropertChanged.
  2. Declare the event. Ex: public event PropertyChangedEventHandler PropertyChanged;
  3. Call OnPropertyChanged nd pass the property name whenever the property is updated Ex: OnPropertyChanged("EmployeeName");
  4. Create the OnPropertyChanged method to raise the event. Ex:
            protected void OnPropertyChanged(string name)
            {
                PropertyChangedEventHandler handler = PropertyChanged;
                if (handler != null)
                {
                    handler(this, new PropertyChangedEventArgs(name));
                }
            }
Code Snippet
  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Text;
  5. using System.Windows;
  6. using System.Windows.Controls;
  7. using System.Windows.Data;
  8. using System.Windows.Documents;
  9. using System.Windows.Input;
  10. using System.Windows.Media;
  11. using System.Windows.Media.Imaging;
  12. using System.Windows.Navigation;
  13. using System.Windows.Shapes;
  14. using System.ComponentModel;
  15.  
  16. namespace Bindingtoclasses
  17. {
  18.     public partial class MainWindow : Window
  19.     {
  20.         public MainWindow()
  21.         {
  22.             InitializeComponent();
  23.             Employee P = new Employee("Hello World");
  24.             this.DataContext = P;
  25.         }
  26.     }
  27.  
  28.     // This class implements INotifyPropertyChanged to support one-way and two-way bindings
  29.     // (such that the UI element updates when the source has been changed dynamically)
  30.     public class Employee : INotifyPropertyChanged
  31.     {
  32.         private string name;
  33.         // Declare the event
  34.         public event PropertyChangedEventHandler PropertyChanged;
  35.  
  36.         public Employee()
  37.         {
  38.         }
  39.  
  40.         public Employee(string value)
  41.         {
  42.             this.name = value;
  43.         }
  44.  
  45.         public string EmployeeName
  46.         {
  47.             get { return name; }
  48.             set
  49.             {
  50.                 name = value;
  51.                 // Call OnPropertyChanged whenever the property is updated
  52.                OnPropertyChanged("EmployeeName");
  53.             }
  54.         }
  55.  
  56.         //// Create the OnPropertyChanged method to raise the event
  57.         protected void OnPropertyChanged(string name)
  58.         {
  59.             PropertyChangedEventHandler handler = PropertyChanged;
  60.             if (handler != null)
  61.             {
  62.                 handler(this, new PropertyChangedEventArgs(name));
  63.             }
  64.         }
  65.     }
  66.  
  67. }

The XAML code to bind the class property to the textbox controls is as follows. To make binding happen, the following should be implemented in the XAML code.

  1. First we need to create an object of the employee class in XAML in the parent element. Ex:
    <Grid.Resources>
            <src:Employee x:Key="myDataSource" EmployeeName="Kishore1021"/>
    </Grid.Resources>

  2. Instead of creating an object in XAML, we can also use DataContext property, create an employee object in the code and assign it to the DataContext as follows
            public MainWindow()
            {
                InitializeComponent();
                Employee P = new Employee("Hello World");
                this.DataContext = P;
            }

  3. I used both in the following sample . Line 16 and 17 uses the local object created in XAML and line 18 uses the DataContext and so directly uses the property name. More info on DataContext in the coming blogs.
  4. Use the Binding Markup Extension “{Binding}” and key in the parameters. In Line 16, I am binding the TextBox.Text to myDataSource object and in that object, I am binding to EmployeeName and the source gets updated when the property gets changed. So as you type, the text in textbox2 also gets changed.
  5. Line 17 also uses the same concept as above except that it doesn’t update the source as the user types. Since the default value of updateSourceTrigger binding property is LostFocus, the textbox1 gets updated only when textbox2 loses focus.
  6. Line 18 uses DataContext and so uses the EmployeeName property directly and binds to textbox3.
    Code Snippet
    1. <Window x:Class="Bindingtoclasses.MainWindow"
    2.         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation&quot;
    3.         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml&quot;
    4.         xmlns:src="clr-namespace:Bindingtoclasses"
    5.  
    6.         Title="MainWindow" Height="350" Width="525">
    7.     <Grid>
    8.         <Grid.Resources>
    9.                 <src:Employee x:Key="myDataSource" EmployeeName="Kishore1021"/>
    10.         </Grid.Resources>
    11.         <Grid.RowDefinitions>
    12.             <RowDefinition Height="*"></RowDefinition>
    13.             <RowDefinition Height="*"></RowDefinition>
    14.             <RowDefinition Height="*"></RowDefinition>
    15.         </Grid.RowDefinitions>
    16.         <TextBox Grid.Row="0" Text="{Binding Source={StaticResource myDataSource}, Path=EmployeeName, UpdateSourceTrigger=PropertyChanged}"/>
    17.         <TextBox Grid.Row="1" Text="{Binding Source= {StaticResource myDataSource}, Path=EmployeeName}"></TextBox>
    18.         <TextBox Grid.Row="2" Text="{Binding Path=EmployeeName}"></TextBox>
    19.         
    20.     </Grid>
    21. </Window>

The output of the program is as follows

image

Download code from Microsoft Skydrive :

Direct Link : https://skydrive.live.com/redir.aspx?cid=38ecce05b21b8b44&amp;resid=38ECCE05B21B8B44!394&amp;parid=38ECCE05B21B8B44!393

"If you’re riding ahead of the herd, take a look back every now and then to make sure it’s still there" – Will Rogers

Binding Object Properties – Source

One of the splendid aspects of the WPF data binding engine is that it can bind to nearly any data source including XML data, ADO.NET classes, LINQ queries, WPF elements, and types that implement IEnumerable or IList. Source – references a Binding‘s data source. By default this object references the element’s DataContext value, which might be inherited from an ancestor element’s DataContext, as discussed in the DataContext section. If you set this property to a non-null value, then the data binding operation will treat that value as the place where data is pushed to and pulled from. A binding configured with the Source property takes precedence over any applied data context.

Ex of Source Objects:

  • You can bind to any CLR objects, including list objects. You can bind to the entire object or public properties, sub-properties, and indexers of the object. Fields are not supported. The binding engine uses CLR reflection to get the values of the properties. Alternatively, objects that implement ICustomTypeDescriptor or have a registered TypeDescriptionProvider also work with the binding engine.
  • You can bind to ADO.NET objects such as DataTable.
  • You can bind to an XmlNode, XmlDocument, or XmlElement, and run XPath queries on them.

As has been discussed earlier, every binding must have a binding target and target property. The binding isn’t complete unless you also specify the data source and source property.

Sometimes you want to show a single value from a data source. It might be showing a font name in a label or an invoice date in a calendar control. Perhaps you’d like to bind the value of one control to the input of another.  Here is an example showing how to bind the Value property of a Slider control to the FontSize property of a TextBlock:

<Slider x:Name='mSlider' Orientation='Horizontal' Minimum='10' Maximum='80' Value='25' />
        <TextBlock Text='Hello World' Margin='5,0' FontSize= '{Binding ElementName=mSlider, Path= Value}'/>
        
        

A binding source is usually a property on an object so you need to provide both the data source object and the data source property in your binding XAML. In the above example the ElementName attribute signifies that you want data from another element on the page and the Path signifies the appropriate property. A binding path can be a complex value, drilling into the member hierarchy, but in this case it’s just the name of the property.

What Can Be a Data Source?: You can use any type as a data source as long as it has a public parameter less constructor and at least one public property. Here’s a sample of binding to System.String. In the example below, we are creating a local resource in the XAML and using that as a Data Source in the binding to bind the TextBox to the local employee object we created in XAML. Coming to TextBlock, we are just saying Text=”{Binding}”, which is setting the textBlock binding in the XAML file and the data context in the code behind: So this TextBlock binds to the EmployeeName string property of the Employee class object we created in the code behind.

  1. <Window x:Class="Bindingtoclasses.MainWindow"
  2.         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation&quot;
  3.         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml&quot;
  4.         xmlns:src="clr-namespace:Bindingtoclasses"
  5.         Title="MainWindow" Height="350" Width="525">
  6.     <Grid >
  7.         <Grid.Resources>
  8.                 <src:Employee x:Key="myDataSource" EmployeeName="Kishore1021"/>
  9.         </Grid.Resources>
  10.         <Grid.RowDefinitions>
  11.             <RowDefinition Height="*"></RowDefinition>
  12.             <RowDefinition Height="*"></RowDefinition>
  13.             <RowDefinition Height="*"></RowDefinition>
  14.             <RowDefinition Height="*"></RowDefinition>
  15.         </Grid.RowDefinitions>
  16.         <TextBox Grid.Row="0" Text="{Binding Source= {StaticResource myDataSource}, Path=EmployeeName}"></TextBox>
  17.         <TextBlock Grid.Row="1" Text="{Binding}"></TextBlock>
  18.             
  19.         </Grid>
  20. </Window>

 

In the C# code-behind file:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.ComponentModel;

namespace Bindingtoclasses
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            Employee P = new Employee("Hello World");
            this.DataContext = P.EmployeeName;
        }
    }

    public class Employee
    {
        private string name;

        public Employee()
        {
        }

        public Employee(string value)
        {
            this.name = value;
        }

        public string EmployeeName
        {
            get { return name; }
            set
            {
                name = value;
            }
        }

    }

}

 

Source code can be downloaded from here.

There are many ways to specify your binding source, that is, to specify where your data is coming from. The simplest way is to instantiate the source object as a resource in XAML and then the Source property of the Binding to that resource

Using the Source property is simpler and more readable. However, if multiple properties bind to the same source, consider using the DataContext property. The DataContext property provides a convenient way to establish a data scope. Say you have many controls and you want all of them to bind to the same source.

<Window x:Class="Bindingtoclasses.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation&quot;
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml&quot;
        xmlns:src="clr-namespace:Bindingtoclasses"

        Title="MainWindow" Height="350" Width="525">
    <Grid DataContext="{Binding Path=.}">
        <Grid.Resources>
                <src:Employee x:Key="myDataSource" EmployeeName="Kishore1021"/>
        </Grid.Resources>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>
        <TextBox Name="TextBox1" Grid.Row="0" Text="{Binding Source={StaticResource myDataSource}, Path=EmployeeName, UpdateSourceTrigger=PropertyChanged}"/>
        <TextBox Name="TextBox2" Grid.Row="1" Text="{Binding Source= {StaticResource myDataSource}, Path=EmployeeName}"></TextBox>
        <TextBox Name="TextBox3" Grid.Row="2" Text="{Binding Path=EmployeeNameTest.EmployeeName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"></TextBox>
        <TextBox Name="TextBox4" Grid.Row="3" Text="{Binding Path=EmployeeNameTest.EmployeeName}"></TextBox>
        <TextBlock Name="TextBlock1" Grid.Row="4" Text="{Binding Path=EmployeeNameTest.EmployeeName}"/>
        <TextBlock Name="TextBlock2" Grid.Row="5" Text="{Binding Path=AnotherField}"/>
        
    </Grid>
</Window>

In this case, you set the DataContext property of your Grid to that source so that all elements in that Grid inherit that common source. <Grid DataContext="{Binding Path=.}"> implies that whatever is the DataContext coming in from the code (In the code it is, this.DataContext = c)will be assigned to the grid. The TextBox3,4 and TextBlock1 in this example both inherit the binding source from the Grid . When you run this, you see TextBox3,4 and TextBlock1 with value “Hello World”.

Download the Source code from Microsoft here.

Priority of Source VS DataContext:
Code Snippet
<Window x:Class="DataBinding_Source_Property.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation&quot;
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml&quot;
        Title="MainWindow" Height="350" Width="525"
        xmlns:kishore="clr-namespace:DataBinding_Source_Property">
   <Window.Resources>
       <kishore:Person x:Key="PersonXAMLDataSource" FullName="Kishore1021"/>
        <kishore:Person x:Key="Person1" FullName="Person1Name"/>
    </Window.Resources>
    
    <Grid DataContext="{StaticResource Person1}">
        <Grid.RowDefinitions>
            <RowDefinition Height="*"> </RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>
        
        <TextBox Grid.Row="0" Text="{Binding Source={StaticResource PersonXAMLDataSource}, Path=FullName}"></TextBox>
        <TextBox Grid.Row="1" Text="{Binding Path=FullName}"/>
    </Grid>
</Window>

 

The first TextBox inherits the DataContext from the parent Grid and has a Source set in the Binding object too. In this case, the binding Source takes priority, causing the TextBox to bind to the Name property of the resource with key “PersonXAMLDataSource” – this displays “kishore1021”. The second inherits the DataContext from the parent Grid causing the TextBox to bind to the Name property of the resource with key “Person1”, causing it to display “Person1Name”.

Most data bound applications tend to use DataContext much more heavily than Source. Use DataContext only when you need to bind more than one property to a particular source. When binding only one property to a source, always use Source. The reason for this is ease of debugging – We can see all the information about the Binding in one place than search for the nearest DataContext to understand what is going on. In a small sample like the one above there is no big advantage, but in complex applications this could save you some time.

Download the source code from Microsoft here

"Management is efficiency in climbing the ladder of success; leadership determines whether the ladder is leaning against the right wall."— Stephen R. Covey

IValueConverter with Markup Extension

We have seen the Introduction to Value Converters in the previous post.  Converter is a Binding property of type IValueConverter. You can set this property to an instance of a class which implements that interface to intercept any movement of data from the binding source to the binding target, or vice versa. Value converters are very convenient and are used quite often.  If you want to use a normal ValueConverter in XAML, you have to add an instance of it to the resources and reference it by using a key. To learn more about instantiating an object as a resource in XAML, see the post. This is cumbersome, because and the key is typically just the name of the converter or you can derive your value converter from MarkupExtension and return its own instance in the ProvideValue override. So you can use it directly without referencing it from the resources.

public override object ProvideValue(IServiceProvider serviceProvider)
{
    throw new NotImplementedException();
}

So to enhance our experience with converters,  derive value converters from MarkupExtension. This way you can create and use it in the binding like this: Text={Binding studentname, Converter={x:MyConverter}}

Following are the steps to create a converter with Markup extension.

  1. Import namespace
    using System.Windows.Markup;

  2. Derive our class from MarkupExtension, IValueConverter
    public class ScoreToColorConverter : MarkupExtension, IValueConverter

  3. Override the ProvideValue method of MarkupExtension class and return this
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return this;
    }

  4. Implement the IValueConverter interface methods Convert & ConvertBack
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        string s = (string) value;
        if (Int32.Parse(s) <= 35)
            return new SolidColorBrush(Colors.Red);
        else
            return new SolidColorBrush(Colors.Green);
    }

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

  5. Specify the xmlns:XXXX in the Window XAML tag
    xmlns:MyXAMLClass="clr-namespace:DataBinding_MultiConverter2"

  6. Specify the UI elements and mention the binding properties. Notice here that we are specifying the Binding converter property as Converter={MyXAMLClass:ScoreToColorConverter}, which is a simple and decent implementation.
    <TextBox Grid.Row="0" Name="TB1" Text="90"></TextBox>
     <TextBox Grid.Row="1" Name="TB2" Background="{Binding ElementName=TB1, Path=Text, Converter={MyXAMLClass:ScoreToColorConverter}}"></TextBox>

The complete XAML is:

<Window x:Class="DataBinding_MultiConverter2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation&quot;
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml&quot;
        Title="MainWindow" Height="350" Width="525"
        xmlns:MyXAMLClass="clr-namespace:DataBinding_MultiConverter2"
        >
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>
        <TextBox Grid.Row="0" Name="TB1" Text="90"></TextBox>
        <TextBox Grid.Row="1" Name="TB2" Background="{Binding ElementName=TB1, Path=Text, Converter={MyXAMLClass:ScoreToColorConverter}}"></TextBox>
    </Grid>
</Window>

The complete source code of the classes used is:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Markup;

namespace DataBinding_MultiConverter2
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class ScoreToColorConverter : MarkupExtension, IValueConverter
    {

        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            return this;
        }

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            string s = (string) value;
            if (Int32.Parse(s) <= 35)
                return new SolidColorBrush(Colors.Red);
            else
                return new SolidColorBrush(Colors.Green);
        }

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

Download the Source code from here. Default conversions may be available because of type converters that are present in the type being bound to. This behavior will depend on which type converters are available in the target. If in doubt, create your own converter.

Following are some typical scenarios where it makes sense to implement a data converter:

  • Your data should be displayed differently, depending on culture. For instance, you might want to implement a currency converter or a calendar date/time converter based on the values or standards used in a particular culture.

  • The data being used is not necessarily intended to change the text value of a property, but is instead intended to change some other value, such as the source for an image, or the color or style of the display text. Converters can be used in this instance by converting the binding of a property that might not seem to be appropriate, such as binding a text field to the Background property of a table cell.

  • More than one control or to multiple properties of controls are bound to the same data. In this case, the primary binding might just display the text, whereas other bindings handle specific display issues but still use the same binding as source information.

  • In the case of a MultiBinding, where a target property has a collection of bindings, you use a custom IMultiValueConverter to produce a final value from the values of the bindings. For example, color may be computed from red, blue, and green values, which can be values from the same or different binding source objects.

See Introduction to Value Converters in the previous post

Download the Source code from here

In organizations, real power and energy is generated through relationships. The patterns of relationships and the capacities to form them are more important than tasks, functions, roles, and positions. –Margaret Wheatley