为什么ItemClick事件处理程序返回上一个单击的项目？

Question

I have a ListView with a ListView ItemTemplate with a grid. I need the information for the row that is clicked and have IsItemClickEnabled=True on the ListView and a ItemClick event handler with a debug that shows the id of the row.

What i cant figure out is why the returned item is always the one that i clicked before, and the first click produces nothing.

Here is the markup for the ListView

<ListView x:Name="ListCustomerView"  ItemsSource="{x:Bind CustomersFromDB}" Grid.Row="1" HorizontalAlignment="Center" IsItemClickEnabled="True" ItemClick="ListCustomerView_ItemClick">
    <ListView.ItemTemplate>
        <DataTemplate>
            <Grid IsTapEnabled="False">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>
                    <ColumnDefinition MinWidth="{StaticResource minColumnWidth}" MaxWidth="{StaticResource maxColumnWidth}"></ColumnDefinition>

                </Grid.ColumnDefinitions>
                <TextBlock Grid.Column="0" Text="{Binding CompanyName}"></TextBlock>
                <TextBlock Grid.Column="1" Text="{Binding FirstName}"></TextBlock>
                <TextBlock Grid.Column="2" Text="{Binding LastName}"></TextBlock>
                <TextBlock Grid.Column="3" Text="{Binding Phone}"></TextBlock>
                <TextBlock Grid.Column="4" Text="{Binding Email}"></TextBlock>
                <TextBlock Grid.Column="5" Text="{Binding Adress}"></TextBlock>
                <TextBlock Grid.Column="6" Text="{Binding PostCode}"></TextBlock>
                <TextBlock Grid.Column="7" Text="{Binding PostArea}"></TextBlock>
                <TextBlock Grid.Column="8" Text="{Binding Comment}"></TextBlock>
            </Grid>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

Here is the code for the CustomersFromDB ItemsSource

public List<Customer> CustomersFromDB { get; set; }
var db = new Database();
CustomersFromDB = db.FetchCustomer();

public List<Customer> FetchCustomer()
{
    using (SQLiteConnection _connection = new SQLiteConnection(sqlitePlatform, dbFilePath))
    {
        List<Customer> customers = new List<Customer>();
        var _customers = _connection.Table<Customer>();
        if (_customers.Count() > 0)
        {
            foreach (Customer customer in _customers)
            {
                customers.Add(customer);
            }
        }
        return customers;
    }
}

And illustration

and the event handler

private void ListCustomerView_ItemClick(object sender, ItemClickEventArgs e)
{
    // BUG! the selected item is not firing correctly ending up outputting the previous clicked item
    Debug.WriteLine((sender as ListView).SelectedItem);
}

The customers are retrieved as seen in the illustration above but when i click a row the id is the previous that is clicked and null if it is the first click.

Why is this wierd behaviour happening?

Answer 1

That's because you're using the sender.SelectedItem which gives you the current selection. The new selection, which is what you want, is only made after the click event. To get the item that you've just clicked, use the e parameter:

private void ListCustomerView_ItemClick(object sender, ItemClickEventArgs e)
{
    Debug.WriteLine(e.ClickedItem.ToString());
}

Alternatively, you can use the SelectionChanged event instead of the ItemClick event. This will give you new selection using the same code like yours:

private void ListCustomerView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    Debug.WriteLine((sender as ListView).SelectedItem.ToString());
}

Answer 2

I haven't tested it, but I'm guessing that the click event happens before the selection event happens. Thus, when your click event handler fires, the selecteditem is whatever is "previously" selected. I believe you're looking for the ClickedItem property on the ItemClickedEventArgs