Wpf converter

This article explains converters and the types of converters with code examples. The WPF converters acts as a bridge between the source and the target if the source and target have different data formats or need some conversion.

For example, sometimes we need to convert data from one format to another format, when it flows from the source to the target or vice-versa the conversion is required. A MultiValue Coverter is required when your target is bound with multiple sources and the source and targets have different data formats or need some conversion. For Example-1, let's say you have three text box controls and one button control and you want to enable the button control when all the text of the text boxes are filled.

View All. Kailash Chandra Behera Updated date, May 16 It explains the types of converters available in WPF and the uses of them. The object that emits the data is called the source and the object that accepts the data is called the target. Value Converters. A Value Converter is required when a target is bound with one source, For instance you have a text box and a button control. You want to enable or disable the button control when the text of text box is filled or null.

MultiValue Coverters. Code Example Next Recommended Article. Getting Started With. NET 5. Getting Started with ML. NET Core.In this article series we will see what are Value Converters and how it can be used and usefulness in WPF. Value Converters The first thing we should ask is; what is Value Converter s?

Well, to say it in simple words it is a Converter that converts value based on input as Source and provides output as Target. Hope the following figure make things easier to understand: As you can see from the above image we have both way arrows in between Source and Target. That means: the value converter not only designed to take input from the target and modify the source, it also works when source data is updated on target.

As you are familiar with two way bindings in WPF. We will straight away create a WPF Application and create simple converters to understand it. Now let's think what simple converter we can use! Let's say we will create one or more Converters. Let's have the following entity class that represent Request structure. As you see in above code display we have an Enum as Status and we have 5 values inside of it; such as: Submitted, Assigned, InProgress, Resolved, and Closed.

Now based on above information we will modify our StatusToColor. As the namespace is not referred, we have to type it upto end and after resolving you would see the following namespace to be used. Now we have to implement the methods in this Interface.

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So resolve the interface again. Select the Implement interface option: the following methods would be defined as follows: As we discussed in the beginning that the Source and Target can convert each other so that's why we have two methods defined.

For the time being we will proceed with Convert method. First we will define the Enum here again. We can use the same name but for understanding I am giving a different name.

Remove the throw new Exception ; and replace with following code. The above code display for converting and returning is a very simple logic to convert. Now for user's knowledge about the colr use we would put the colors with some information. Now we have bind the converter in the XAML, for that first thing we have to do is to use the namespace. Now for the Rectangle in TemplateColumn we will fill using the Converter: We are good to go, and run the application.

But before that let's have some sample data to display. You would see the colors are reflected as per the data given. Hope this article helps. View All.

wpf converter

Diptimaya Patra Updated date, Sep 29 Next Recommended Article. Getting Started With. NET 5. Getting Started with ML. NET Core.This topic introduces the purpose of type conversion from string as a general XAML language feature.

In the. NET Framework, the TypeConverter class serves a particular purpose as part of the implementation for a managed custom class that can be used as a property value in XAML attribute usage.

If you write a custom class, and you want instances of your class to be usable as XAML settable attribute values, you might need to apply a TypeConverterAttribute to your class, write a custom TypeConverter class, or both. When you set an attribute value in a XAML file, the initial type of that value is a string in pure text. A XAML processor needs two pieces of information in order to process an attribute value. The first piece of information is the value type of the property that is being set.

Any string that defines an attribute value and that is processed in XAML must ultimately be converted or resolved to a value of that type.

If the value is a primitive that is understood by the XAML parser such as a numeric valuea direct conversion of the string is attempted.

If the value is an enumeration, the string is used to check for a name match to a named constant in that enumeration. If the value is neither a parser-understood primitive nor an enumeration, then the type in question must be able to provide an instance of the type, or a value, based on a converted string. This is done by indicating a type converter class. The type converter is effectively a helper class for providing values of another class, both for the XAML scenario and also potentially for code calls in.

WPF Value Converters

NET code. Depending on your familiarity with the underlying XAML concepts, you may already be using type conversion behavior in basic application XAML without realizing it.

For instance, WPF defines literally hundreds of properties that take a value of type Point. A Point is a value that describes a coordinate in a two-dimensional coordinate space, and it really just has two important properties: X and Y.

When you specify a point in XAML, you specify it as a string with a delimiter typically a comma between the X and Y values you provide.

Xamarin.Forms Binding Value Converters

In this case that is the class PointConverter. The type converter for Point defined at the class level streamlines the markup usages of all properties that take Point. Without a type converter here, you would need the following much more verbose markup for the same example shown previously:.

Whether to use the type conversion string or a more verbose equivalent syntax is generally a coding style choice. Your XAML tooling workflow might also influence how values are set. Some XAML tools tend to emit the most verbose form of the markup because it is easier to round-trip to designer views or its own serialization mechanism.

Value Converters in WPF

Existing type converters can generally be discovered on WPF and. This attribute will name the class that is the supporting type converter for values of that type, for XAML purposes as well as potentially other purposes. Markup extensions and type converters fill orthogonal roles in terms of XAML processor behavior and the scenarios that they are applied to.

Although context is available for markup extension usages, type conversion behavior of properties where a markup extension provides a value is generally is not checked in the markup extension implementations. In other words, even if a markup extension returns a text string as its ProvideValue output, type conversion behavior on that string as applied to a specific property or property value type is not invoked, Generally, the purpose of a markup extension is to process a string and return an object without any type converter involved.

One common situation where a markup extension is necessary rather than a type converter is to make a reference to an object that already exists. At best, a stateless type converter could only generate a new instance, which might not be desirable. In the WPF and. NET Framework implementation of the XAML parser, there are certain types that have native type conversion handling, yet are not types that might conventionally be thought of as primitives.

An example of such a type is DateTime. The reason for this is based on how the.Although they share some characteristics, type converters and markup extensions are represented differently in a XAML node stream.

In this documentation set, type converters, markup extensions, and similar constructs are sometimes collectively referred to as value converters. In XAML, value converters are used for various scenarios. The following list shows the different types of value converters in XAML:. TypeConverter is a class that was in the. Its original purpose was to support property windows and similar text-based editing metaphors for IDE properties.

The introduction of XAML to. TypeConverter can also be used to serialize an object value to text syntax. Markup extensions are a concept that in this form is originated by the XAML language.

You can think of a markup extension as being something like an extensible escape sequence that calls into a service class to provide its logic. Markup extensions differ from type converters. Type converters are typically associated with types or members. They are invoked when an object graph creation or a serialization encounters text syntax that is associated with those entities. Markup extensions are associated with a single supporting service class, but can be applied for any member value.

However, you can implement your markup extension to deliberately restrict its use to certain members or destination types, by using service context. Markup extensions can override a type converter association. Or you can use them to specify an attribute value for members that would not otherwise support a text syntax. A ValueSerializer is a specialized type converter that is optimized for converting an object to a string.

A ValueSerializer implementation obtains services in a manner that is like a TypeConverter implementation.

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The virtual methods provide an input context parameter. ValueSerializer property. TypeConverter and XamlType. ValueSerializer exist, the type converter should be used for the load path and the value serializer should be used for the save path. If XamlType. TypeConverter exists but XamlType. ValueSerializer is nullthe type converter is also used for the save path.

A value converter is extensible beyond the specific patterns of a type converter or a markup extension. However, this customization would also require the redefinition of the XAML type system as provided by. The existing XAML type system has representations and reporting systems for type converters, markup extensions, and value serializers, but not for custom forms of value conversion.

Markup extensions and type converters are used for different situations in XAML. Although context is available for markup extension usages, type conversion behavior of properties where a markup extension provides a value is generally is not checked in the markup extension implementations.

In other words, even if a markup extension returns a text string as its ProvideValue output, type conversion behavior on that string as applied to a specific property or property value type is not invoked.Download the sample. Data bindings usually transfer data from a source property to a target property, and in some cases from the target property to the source property.

wpf converter

This transfer is straightforward when the source and target properties are of the same type, or when one type can be converted to the other type through an implicit conversion.

When that is not the case, a type conversion must take place. In the String Formatting article, you saw how you can use the StringFormat property of a data binding to convert any type into a string. For other types of conversions, you need to write some specialized code in a class that implements the IValueConverter interface. Data namespace, but this IValueConverter is in the Xamarin.

Forms namespace. Classes that implement IValueConverter are called value convertersbut they are also often referred to as binding converters or binding value converters. Suppose you want to define a data binding where the source property is of type int but the target property is a bool. You want this data binding to produce a false value when the integer source is equal to 0, and true otherwise.

Converters in WPF

You set an instance of this class to the Converter property of the Binding class or to the Converter property of the Binding markup extension. This class becomes part of the data binding. The Convert method is called when data moves from the source to the target in OneWay or TwoWay bindings. The value parameter is the object or value from the data-binding source. The method must return a value of the type of the data-binding target.

The method shown here casts the value parameter to an int and then compares it with 0 for a bool return value. ConvertBack performs the opposite conversion: It assumes the value parameter is a bool from the target, and converts it to an int return value for the source. If the data binding also includes a StringFormat setting, the value converter is invoked before the result is formatted as a string.

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The Enable Buttons page in the Data Binding Demos sample demonstrates how to use this value converter in a data binding. The IntToBoolConverter is instantiated in the page's resource dictionary.

wpf converter

It is then referenced with a StaticResource markup extension to set the Converter property in two data bindings. It is very common to share data converters among multiple data bindings on the page:. If a value converter is used in multiple pages of your application, you can instantiate it in the resource dictionary in the App. The Enable Buttons page demonstrates a common need when a Button performs an operation based on text that the user types into an Entry view.

If nothing has been typed into the Entrythe Button should be disabled. Each Button contains a data binding on its IsEnabled property. The data-binding source is the Length property of the Text property of the corresponding Entry. If that Length property is not 0, the value converter returns true and the Button is enabled:.

Notice that the Text property in each Entry is initialized to an empty string. The Text property is null by default, and the data binding will not work in that case. Some value converters are written specifically for particular applications, while others are generalized.A Value Converter functions as a bridge between a target and a source and it is necessary when a target is bound with one source, for instance you have a text box and a button control.

You want to enable or disable the button control when the text of the text box is filled or null. Code Example1: Declaration of Value Converter class. Here in the preceding code I have written code in the convert method to enable or disable the button control and have not written any code in the ConvertBack function. To use the convert back I have another example. Let's say you have a check box control bound the text with the text of text box control.

You want to determine whether the check box is checked when the text is married and unchecked when the text is unmarried. In the preceding code, I am checking the text of text box. If it is married then the convert function returns true that will make the check box checked otherwise it will uncheck the checkbox. The convert back function is doing as said above, if the check box is checked it is setting the text of the TextBox to Married and otherwise Unmarried.

After declaring the resource there is the need to use it with binding. See the following XAML code example. View All. Kailash Chandra Behera Updated date, May 16 In this case you need to convert the string data to Boolean. This is possible using a Value Converter. Data namespace and implement the two methods Convert and ConvertBack. The bound object that emits the data is called the Source and the other that accepts the data is called the Target.

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Getting Started With. NET 5. Getting Started with ML. NET Core.So far we have used some simple data bindings, where the sending and receiving property was always compatible. However, you will soon run into situations where you want to use a bound value of one type and then present it slightly differently.

Value converters are very frequently used with data bindings. Here are some basic examples:. These are some of the simple cases, but there are many more.

TypeConverters and XAML

For instance, you may want to check a checkbox based on a Boolean value, but you want it reversed, so that the CheckBox is checked if the value is false and not checked if the value is true. You can even use a converter to generate an image for an ImageSource, based on the value, like a green sign for true or a red sign for false - the possibilities are pretty much endless!

For cases like this, you can use a value converter. These small classes, which implement the IValueConverter interface, will act like middlemen and translate a value between the source and the destination.

So, in any situation where you need to transform a value before it reaches its destination or back to its source again, you likely need a converter.

Both interfaces just requires you to implement two methods: Convert and ConvertBack. As the name implies, these methods will be used to convert the value to the destination format and then back again.

Let's implement a simple converter which takes a string as input and then returns a Boolean value, as well as the other way around.

wpf converter

If you're new to WPF, and you likely are since you're reading this tutorial, then you might not know all of the concepts used in the example, but don't worry, they will all be explained after the code listings:.

So, let's start from the back and then work our way through the example. As advertised, it just implements the two required methods, called Convert and ConvertBack. The Convert methods assumes that it receives a string as the input the value parameter and then converts it to a Boolean true or false value, with a fallback value of false.

For fun, I added the possibility to do this conversion from French words as well. The ConvertBack method obviously does the opposite: It assumes an input value with a Boolean type and then returns the English word "yes" or "no" in return, with a fallback value of "no".

You may wonder about the additional parameters that these two methods take, but they're not needed in this example. We'll use them in one of the next chapters, where they will be explained. In the XAML part of the program, we start off by declaring an instance of our converter as a resource for the window. We then have a TextBox, a couple of TextBlocks and a CheckBox control and this is where the interesting things are happening: We bind the value of the TextBox to the TextBlock and the CheckBox control and using the Converter property and our own converter reference, we juggle the values back and forth between a string and a Boolean value, depending on what's needed.

If you try to run this example, you will be able to change the value in two places: By writing "yes" in the TextBox or any other value, if you want false or by checking the CheckBox. No matter what you do, the change will be reflected in the other control as well as in the TextBlock. This was an example of a simple value converter, made a bit longer than needed for illustrational purposes.

In the next chapter we'll look into a more advanced example, but before you go out and write your own converter, you might want to check if WPF already includes one for the purpose.

As of writing, there are more than 20 built-in converters that you may take advantage of, but you need to know their name. WPF Tutorial.