Data binding is a great way to display your data. This step-by-step tutorial will teach you the basics. If you are already familiar with data binding you can skip this tutorial.
Data binding provides a simple and consistent way for applications to present and interact with data. Elements can be bound to data from a variety of data sources in the form of common language runtime (CLR) objects and XML. ContentControls such as Button
and ItemsControls such as ListBox and ListView have built-in functionality to enable flexible styling of single data items or collections of data items. Sort, filter, and group views can be generated on top of the data.
To explain the basics of data binding we will create a simple Windows Phone 7 application. This application contains four textboxes which will show the three ways of data binding:
What do they mean ?
OneTime binding sends data from the source to the target; however, it does this only when the application is started or when the DataContext changes and, as a result, does not listen for change notifications in the source.
When using OneWay binding the data flows from the source to the target each time a change is made on the source. OneWay binding is the default binding mode for the TextBlock's Text property and does not need to be specified.
TwoWay binding sends the source data to the target, and if there are changes in the target property's value, those will be sent back to the source.
Let’s create the application stub. For this demo I will use Expression Blend, because its support for XAML-based tooling, especially data binding, is great and designer as well as developers can profit from it.
Name the projects as you want. After Blend has finished the creation of the project we will see the following screen
To show the functionality of the three data binding ways we will put four textboxes on our design surfaces. The first textbox will be the
source, textbox number two will demonstrate OneTime
binding, textbox number three OneWay binding, and the last textbox
TwoWay binding. The application should now look something like this:
Now we will come to the exciting part. Click the second textbox from the top. You should see the
Properties window (if not go to Window menu and select Properties option). In the
Properties window go to Common Properties where you can find the
Text property. On the right of it you can see a small white point. Click it and in the context menu choose
You should now see the Create Data Binding menu.
Choose the Element Property tab. At Scene elements choose the top textbox and on
Properties the Text property. After you have done this slide down the accordion and select
OneTime binding direction.
Do the same for the third textbox (with OneWay binding) and for the fourth textbox (with TwoWay binding). Don’t forget to mark the first textbox as the source element. If you are ready start the project. It should look something like this:
Now we will test our data binding. Change the text in the first textbox. You should see that the third and the fourth text will react to the changes immediately. But what happens with our second? Like said above, OneTime binding will only work the first
time when the DataContext will be set. After that the binding will be deleted and changes are not reflected on it.
Let’s have a look at the OneWay binding. Like you have seen the third textbox reacts on changes of the first textbox. Does this also work in the other direction? Try it! You will see that the first textbox will keep its value.
The last binding mode is TwoWay binding. You have already seen that the fourth textbox reacts on changes of the first textbox immediately, but it should also do it in the other direction. Really?
Make some changes to the fourth textbox. Mh? The text of the first textbox does not react immediately on the changes, but why? This example shows how smart data binding is. In this case the text property of the first textbox will only be set if the fourth textbox
will lose the focus. Why is that smart? Imagine it would not do that. In that case it will go into an infinite loop where the two textboxes will update each other.
With that we are finished and you can take the next steps in getting a data binding ninja.
You can download the sample project from the
MSDN Samples site.
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