Updating listbox from code behind

03-Nov-2019 23:43 by 2 Comments

Updating listbox from code behind - who is niall horan dating december 2016

There are two different scenarios that you may or may not want to handle when dealing with data source changes: Changes to the list of items and changes in the bound properties in each of the data objects.How to handle them may vary, depending on what you're doing and what you're looking to accomplish, but WPF comes with two very easy solutions that you can use: The Observable Collection and the INotify Property Changed interface.

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Try running the example on your own machine and see how the three textboxes act completely different: The first value doesn't update before you click the button, the second value isn't updated until you leave the Text Box, while the third value updates automatically on each keystroke, text change etc.

The Update Source Trigger property of a binding controls how and when a changed value is sent back to the source.

However, since WPF is pretty good at controlling this for you, the default value should suffice for most cases, where you will get the best mix of a constantly updated UI and good performance.

The following example will show you why we need these two things: Try running it for yourself and watch how even though you add something to the list or change the name of one of the users, nothing in the UI is updated.

The example is pretty simple, with a User class that will keep the name of the user, a List Box to show them in and some buttons to manipulate both the list and its contents.

The Items Source of the list is assigned to a quick list of a couple of users that we create in the window constructor.

The problem is that none of the buttons seems to work. The first step is to get the UI to respond to changes in the list source (Items Source), like when we add or delete a user.

This is the price you will have to pay if you want to bind to your own classes and have the changes reflected in the UI immediately.

Obviously you only have to call Notify Property Changed in the setter's of the properties that you bind to - the rest can remain the way they are.

The second Text Box uses the Lost Focus value, which is actually the default for a Text binding.

It means that the source value will be updated each time the destination control loses focus.

By doing that, our User objects are capable of alerting the UI layer of changes to its properties.