Updating ListView ItemsSource after setting/clearing it

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I have a listview and a button which when clicked loads the listview with some items from an xml file. When the user clicks it again (because they might want to update the data in the listview to see if it has changed) it throws a NullReferenceException. Now I understand why this is thrown, it is because I am using this code to reload a listview after creating a list of items:

C#

// Remove and clear source [1]
timeSteps.ItemsSource = null;
timeSteps.Items.Clear();
// The list<> has been updated so reload the listview [2]
timeSteps.ItemsSource = timesteps;
// Select the first item and focus the control [3]
timeSteps.SelectedIndex = 0;
timeSteps.Focus();

I know that the error occurs at [1] because one of the items is selected and the SelectedItem property cannot be set to null so when the items are removed it throws an exception. How can I make is so the list can be reloadable when the user reclicks the button (otherwise they have to switch and go back to the page in the containing frame which works because all controls are reset so no exception is thrown. I don't really want to change the way I bind the items to the listview if I can help it but I can see why that might be the only option. The binding is a simple one:

XML

<ListView.View>
    <GridView>
        <GridViewColumn DisplayMemberBinding="{Binding TimeStepItem}" Header="Date" Width="135"/>
    </GridView>
</ListView.View>

C#

public class TimeStep
{
    public string TimeStepItem { get; set; }
    public string Link { get; set; }
}

With the usual list<> which I fill with TimeStepItems.

Posted 29-Nov-13 4:55am

Henry Hunt

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Member 14598472 7-Nov-19 2:14am

But I Use
timeSteps.ItemsSource = null;
timeSteps.Items.Clear();

This Line And It's Working For Update Listview In Ui Side

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AnthonyMG · Accepted Answer · 2013-11-29T06:50:00

You are getting the exception here because you are making the itemsource to null and then trying to clear the items in it(rather it should be the opposite)

1. Use Observable Collection Which is meant for performing (Read,Update,Delete) operation dynamically to a collection

2.No need to make the itemsource to null, rather just clear the itemsource and re-assign with new values.

Improved Answer:

Try below code for using ObservableCollection in ListView

XML

private ObservableCollection<TimeStepData> timeStepDataCollection;
    public ObservableCollection<TimeStepData> TimeStepDataCollection
    {
        get
        {
            if (timeStepDataCollection== null)
            {
                timeStepDataCollection= new ObservableCollection<TimeStepData>();
            }
            return timeStepDataCollection;
        }
        set
        {
    timeStepDataCollection = value;
        }
    }

    //created a class for TimeStepData
    public  class TimeStepData
    {
        public string TimeStepItem1{ get; set; }
        public string TimeStepItem2{ get; set; }
        public string TimeStepItem3{ get; set; }
    }


// In XAML :

<ListView Height="96" Name="listView1" Width="226" ItemsSource="{Binding  TimeStepDataCollection}">
             <ListView.View>
              <GridView>
                <GridViewColumn Width="50" Header="Name"   DisplayMemberBinding="{Binding TimeStepItem1/>
                <GridViewColumn Width="70" Header="Class" DisplayMemberBinding="{Binding TimeStepItem2/>
                <GridViewColumn Width="70" Header="Status" DisplayMemberBinding="{Binding TimeStepItem3/>
              </GridView>
            </ListView.View>
       </ListView>