如何访问 WPF ListView 的 ListViewItems?
题
在一个事件中,我想将焦点放在 ListViewItem 模板中的特定 TextBox 上。XAML 看起来像这样:
<ListView x:Name="myList" ItemsSource="{Binding SomeList}">
<ListView.View>
<GridView>
<GridViewColumn>
<GridViewColumn.CellTemplate>
<DataTemplate>
<!-- Focus this! -->
<TextBox x:Name="myBox"/>
我在后面的代码中尝试了以下操作:
(myList.FindName("myBox") as TextBox).Focus();
但我似乎误解了 FindName()
文档,因为它返回 null
.
还有 ListView.Items
没有帮助,因为(当然)包含我绑定的业务对象并且没有 ListViewItems。
也不 myList.ItemContainerGenerator.ContainerFromItem(item)
, ,它也返回 null。
解决方案
了解原因 ContainerFromItem
不适合我,这里有一些背景。我需要此功能的事件处理程序如下所示:
var item = new SomeListItem();
SomeList.Add(item);
ListViewItem = SomeList.ItemContainerGenerator.ContainerFromItem(item); // returns null
之后 Add()
这 ItemContainerGenerator
不会立即创建容器,因为 CollectionChanged
事件可以在非 UI 线程上处理。相反,它启动异步调用并等待 UI 线程回调并执行实际的 ListViewItem 控件生成。
要在发生这种情况时收到通知, ItemContainerGenerator
暴露了一个 StatusChanged
生成所有容器后触发的事件。
现在我必须监听这个事件并决定控件当前是否想要设置焦点。
其他提示
正如其他人所指出的,通过在 ListView 上调用 FindName 无法找到 myBox TextBox。但是,您可以获取当前选定的ListViewItem,并使用VisualTreeHelper 类从ListViewItem 获取TextBox。这样做看起来像这样:
private void myList_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (myList.SelectedItem != null)
{
object o = myList.SelectedItem;
ListViewItem lvi = (ListViewItem)myList.ItemContainerGenerator.ContainerFromItem(o);
TextBox tb = FindByName("myBox", lvi) as TextBox;
if (tb != null)
tb.Dispatcher.BeginInvoke(new Func<bool>(tb.Focus));
}
}
private FrameworkElement FindByName(string name, FrameworkElement root)
{
Stack<FrameworkElement> tree = new Stack<FrameworkElement>();
tree.Push(root);
while (tree.Count > 0)
{
FrameworkElement current = tree.Pop();
if (current.Name == name)
return current;
int count = VisualTreeHelper.GetChildrenCount(current);
for (int i = 0; i < count; ++i)
{
DependencyObject child = VisualTreeHelper.GetChild(current, i);
if (child is FrameworkElement)
tree.Push((FrameworkElement)child);
}
}
return null;
}
我注意到问题标题与问题内容没有直接关系,接受的答案也没有回答它。我已经能够通过使用以下方法“访问 WPF ListView 的 ListViewItems”:
public static IEnumerable<ListViewItem> GetListViewItemsFromList(ListView lv)
{
return FindChildrenOfType<ListViewItem>(lv);
}
public static IEnumerable<T> FindChildrenOfType<T>(this DependencyObject ob)
where T : class
{
foreach (var child in GetChildren(ob))
{
T castedChild = child as T;
if (castedChild != null)
{
yield return castedChild;
}
else
{
foreach (var internalChild in FindChildrenOfType<T>(child))
{
yield return internalChild;
}
}
}
}
public static IEnumerable<DependencyObject> GetChildren(this DependencyObject ob)
{
int childCount = VisualTreeHelper.GetChildrenCount(ob);
for (int i = 0; i < childCount; i++)
{
yield return VisualTreeHelper.GetChild(ob, i);
}
}
我不确定递归有多忙,但在我的情况下它似乎工作得很好。不,我没有使用过 yield return
在之前的递归上下文中。
您可以向上遍历 ViewTree 来查找该项目 '列表视图项' 对应于命中测试触发的单元格的记录集。
同样,您可以从父视图获取列标题来比较和匹配单元格的列。您可能希望将单元格名称绑定到列标题名称,作为比较器委托/过滤器的键。
例如:HitResult 在 TextBlock 上以绿色显示。您希望获得 '列表视图项'.
/// <summary>
/// ListView1_MouseMove
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void ListView1_MouseMove(object sender, System.Windows.Input.MouseEventArgs e) {
if (ListView1.Items.Count <= 0)
return;
// Retrieve the coordinate of the mouse position.
var pt = e.GetPosition((UIElement) sender);
// Callback to return the result of the hit test.
HitTestResultCallback myHitTestResult = result => {
var obj = result.VisualHit;
// Add additional DependancyObject types to ignore triggered by the cell's parent object container contexts here.
//-----------
if (obj is Border)
return HitTestResultBehavior.Stop;
//-----------
var parent = VisualTreeHelper.GetParent(obj) as GridViewRowPresenter;
if (parent == null)
return HitTestResultBehavior.Stop;
var headers = parent.Columns.ToDictionary(column => column.Header.ToString());
// Traverse up the VisualTree and find the record set.
DependencyObject d = parent;
do {
d = VisualTreeHelper.GetParent(d);
} while (d != null && !(d is ListViewItem));
// Reached the end of element set as root's scope.
if (d == null)
return HitTestResultBehavior.Stop;
var item = d as ListViewItem;
var index = ListView1.ItemContainerGenerator.IndexFromContainer(item);
Debug.WriteLine(index);
lblCursorPosition.Text = $"Over {item.Name} at ({index})";
// Set the behavior to return visuals at all z-order levels.
return HitTestResultBehavior.Continue;
};
// Set up a callback to receive the hit test result enumeration.
VisualTreeHelper.HitTest((Visual)sender, null, myHitTestResult, new PointHitTestParameters(pt));
}
我们对 WPF 的新数据网格使用类似的技术:
Private Sub SelectAllText(ByVal cell As DataGridCell)
If cell IsNot Nothing Then
Dim txtBox As TextBox= GetVisualChild(Of TextBox)(cell)
If txtBox IsNot Nothing Then
txtBox.Focus()
txtBox.SelectAll()
End If
End If
End Sub
Public Shared Function GetVisualChild(Of T As {Visual, New})(ByVal parent As Visual) As T
Dim child As T = Nothing
Dim numVisuals As Integer = VisualTreeHelper.GetChildrenCount(parent)
For i As Integer = 0 To numVisuals - 1
Dim v As Visual = TryCast(VisualTreeHelper.GetChild(parent, i), Visual)
If v IsNot Nothing Then
child = TryCast(v, T)
If child Is Nothing Then
child = GetVisualChild(Of T)(v)
Else
Exit For
End If
End If
Next
Return child
End Function
该技术应该非常适合您,只需在生成后传递您的列表视图项即可。
或者可以简单地通过以下方式完成
private void yourtextboxinWPFGrid_LostFocus(object sender, RoutedEventArgs e)
{
//textbox can be catched like this.
var textBox = ((TextBox)sender);
EmailValidation(textBox.Text);
}