如何访问XAML DataTemplate中的控件？

Question

我有这个翻转视图:

<FlipView x:Name="models_list" SelectionChanged="selectionChanged">
 <FlipView.ItemTemplate>
          <DataTemplate>
                <Grid x:Name="cv">
                        <Image x:Name="img1" Source = "{Binding ModelImage}" Stretch="Fill" Tag="{Binding ModelTag}"/>
                </Grid>
           </DataTemplate>
  </FlipView.ItemTemplate>

我想找到当前所选索引的img1.在搜索它时,我在这里的一些帖子中找到了这个方法:

private DependencyObject FindChildControl<T>(DependencyObject control, string ctrlName)
    {
        int childNumber = VisualTreeHelper.GetChildrenCount(control);
        for (int i = 0; i < childNumber; i++)
        {
            DependencyObject child = VisualTreeHelper.GetChild(control, i);
            FrameworkElement fe = child as FrameworkElement;
            // Not a framework element or is null
            if (fe == null) return null;

            if (child is T && fe.Name== ctrlName)
            {
                // Found the control so return
                return child;
            }
            else
            {
                // Not found it - search children
                DependencyObject nextLevel = FindChildControl<T>(child, ctrlName);
                if (nextLevel != null)
                    return nextLevel;
            }
        }
        return null;
    }

它返回我在flipview的第一个索引上的图像,但我需要当前所选索引上的一个..我试图编辑此方法但我无法找到所需的控件.谁能帮我？

Answer 1

您遇到的问题DataTemplate是重复并且内容是由内容生成的FlipView.在Name不被暴露,因为它将与已生成的上一个兄弟(或下一个将要)发生冲突.

因此,要获取命名元素,DataTemplate您必须首先获取生成的项目,然后在该生成的项目内搜索所需的元素.请记住,XAML中的逻辑树是您按名称访问事物的方式.生成的项目不在逻辑树中.相反,它们位于Visual Tree中(所有控件都在Visual Tree中).这意味着它必须在Visual Tree中搜索您要引用的控件.将VisualTreeHelper让你做到这一点.

现在,该怎么办？

我写这个文章,因为它是这样一个反复出现的问题:http://blog.jerrynixon.com/2012/09/how-to-access-named-control-inside-xaml.html但解决方案的肉一个看起来像这样的递归方法:

public void TestFirstName()
{
    foreach (var item in MyFlipView.Items)
    {
        var _Container = MyFlipView.ItemContainerGenerator
            .ContainerFromItem(item);
        var _Children = AllChildren(_Container);

        var _FirstName = _Children
            // only interested in TextBoxes
            .OfType<TextBox>()
            // only interested in FirstName
            .First(x => x.Name.Equals("FirstName"));

        // test & set color
        _FirstName.Background = 
            (string.IsNullOrWhiteSpace(_FirstName.Text))
            ? new SolidColorBrush(Colors.Red)
            : new SolidColorBrush(Colors.White);
    }
}

public List<Control> AllChildren(DependencyObject parent)
{
    var _List = new List<Control>();
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
    {
        var _Child = VisualTreeHelper.GetChild(parent, i);
        if (_Child is Control)
            _List.Add(_Child as Control);
        _List.AddRange(AllChildren(_Child));
    }
    return _List;
}

这里的关键问题是像这样的方法获取所有子项,然后在结果的子控件列表中,您可以搜索所需的特定控件.合理？

现在回答你的问题!

因为您特别想要当前选择的项目,所以您只需更新代码如下:

if (MyFlipView.SelectedItem == null)
    return;
var _Container = MyFlipView.ItemContainerGenerator
    .ContainerFromItem(MyFlipView.SelectedItem);
// then the same as above...

Answer 2

也许更通用的方法可能是这样的:

private List<Control> AllChildren(DependencyObject parent)
{
    var _List = new List<Control>();
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
    {
       var _Child = VisualTreeHelper.GetChild(parent, i);
       if (_Child is Control)
       {
        _List.Add(_Child as Control);
       }
      _List.AddRange(AllChildren(_Child));
    }
    return _List;
 } 


private T FindControl<T> (DependencyObject parentContainer, string controlName)
{            
        var childControls = AllChildren(parentContainer);
        var control = childControls.OfType<Control>().Where(x => x.Name.Equals(controlName)).Cast<T>().First();           
        return control;
}

你会像这样调用FindControl:

var parentContainer = this.flipView.ItemContainerGenerator.ContainerFromItem(this.flipView.SelectedItem);
var myImage = FindControl<Image>(parentContainer, "img1");

//suppose you want to change the visibility
myImage.Visibility = Windows.UI.Xaml.Visibility.Collapsed;