WPF: How do i limit number of items in Combobox

Question

0.00/5 (No votes)

See more:

I've created a WPF custom ComboBox which has the ability to filter items according to a "search string". The ComboBox ItemsSource is bound to a ObservableCollection.

The ObservableCollection is a collection of "Person" object. It exposes a property "Usage Count".

Now if the "search string" is empty i have to show the Top 30 records from the ObservableCollection. The "UsageCount" property in the "Person" class decides the Top 30 Records(i.e. the the Top 30 records with the maximum UsageCount has to be displayed). The UsageCount property changes dynamically. How do i achieve this.. Please help. Thanks in advance :)

Posted 30-Apr-12 22:05pm

tomgeo19

Add a Solution

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Pete O'Hanlon · Answer 1 · 2012-05-01T00:27:00

As you have rightly identified, the ObservableCollection is not quite the right tool for the job here, so what do you do? Well, fortunately for us, WPF provides something called the CollectionView which you can think of as a wrapper around a collection. In order to use it, expose the item that you want to bind on as an ICollectionView item like this:

C#

public ICollectionView MyView { get; private set; }

Now, you fill it like this:

C#

IList<Person> people = GetPeople();
MyView = CollectionViewSource.GetDefaultView(people);

Finally, you just need to filter the data (using whatever algorithm you need to filter this list on) and then update the ICollectionView using

C#

MyView.Refresh();

VJ Reddy · Answer 2 · 2012-05-01T00:13:00

I have not tested but I think the following may be helpful.

1. Implement INotifyPropertyChanged interface and in the setter of UsageCount property, call the PropertyChanged event handler method.
2. In the PropertyChanged event handler method set the DataContext using LINQ query as explained here http://msdn.microsoft.com/en-us/library/bb910060.aspx[^]
3. The following LINQ query can be used.

C#

this.DataContext = Persons.OrderBy (p => p.UsageCount, new descendingOrderComparer()).Take(30);

//Assuming that the UsageCount is of type int.
//For descending order comparison, Comparer is required.
public class descendingOrderComparer  : IComparer<int> {
	public int Compare(int first, int second)  {
		return second - first;
	}
}

WPF: How do i limit number of items in Combobox

2 solutions

Solution 3

Solution 2

Add your solution here

Preview 0