将ItemsControl中的一个新项目滚动到视图中 [英] Scroll a new item in a ItemsControl into view

问题描述

我有一个 ItemsControl ，它是数据绑定到一个 ObservableCollection 。我在代码背后有这个方法，在列表中添加一个新的模型。我想将新项目（列表底部）滚动到视图中。

我认为 ItemsControl 在查询大小时尚未更新，因为添加模型之前和之后的 ActualHeight 是相同的。此代码的效果是滚动到略高于新项目的点。

我如何知道新的 ActualHeight 将是？

这是我的代码：

  ViewModel.CreateNewChapter（）; 
 var height = DocumentElements.ActualHeight; 
 var width = DocumentElements.ActualWidth; 
 DocumentElements.BringIntoView（new Rect（0，height  -  1，width，1））; 
  

解决方案

我想你需要调用 BringIntoView 在项目容器上，而不是ItemsControl本身：

  var container = DocumentElements.ItemContainerGenerator。 ContainerFromItem（model）as FrameworkElement; 
 if（container！= null）
 container.BringIntoView（）; 
  

---

编辑：实际上这不行，因为在这一点上，项目容器尚未生成...您可以处理 ItemContainerGenerator StatusChanged 事件c>。我尝试了以下代码：

  public static class ItemsControlExtensions 
 {
 public static void BringItemIntoView（this ItemsControl itemsControl，object item）
 {
 var generator = itemsControl.ItemContainerGenerator; 
 
 if（！TryBringContainerIntoView（generator，item））
 {
 EventHandler handler = null; 
 handler =（sender，e）=> 
 {
 switch（generator.Status）
 {
 case GeneratorStatus.ContainersGenerated：
 TryBringContainerIntoView（generator，item）; 
 break; 
 case GeneratorStatus.Error：
 generator.StatusChanged  -  = handler; 
 break; 
 case GeneratorStatus.GeneratingContainers：
 return; 
 case GeneratorStatus.NotStarted：
 return; 
默认值：
 break; 
} 
}; 
 
 generator.StatusChanged + = handler; 
 
 
 
 private static bool TryBringContainerIntoView（ItemContainerGenerator生成器，对象项）
 {
 var container = generator.ContainerFromItem（item）as FrameworkElement; 
 if（container！= null）
 {
 container.BringIntoView（）; 
返回true; 
} 
返回false; 
} 
} 
  

但是它不适用于...某些原因， ContainerFromItem 在状态更改为 ContainersGenerated 后仍返回null，我不知道为什么： p>

---

编辑：好的，我现在明白了...这是因为虚拟化：容器只有当他们需要被显示，所以不会为隐藏的物品生成容器。如果您为ItemsControl（ VirtualizingStackPanel.IsVirtualizing =False）切换虚拟化，上述解决方案可以正常运行。

I have an ItemsControl that is databound to a ObservableCollection. I have this method in the code behind which adds a new model to the list. I would then like to scroll the new item (at the bottom of the list) into view.

I think the size of the ItemsControl is not yet updated when I am querying the size, since the ActualHeight before and after the addition of the model is the same. The effect of this code is to scroll to a point slightly above the new item.

How would I know what the new ActualHeight is going to be?

Here is my code:

        ViewModel.CreateNewChapter();
        var height = DocumentElements.ActualHeight;
        var width = DocumentElements.ActualWidth;
        DocumentElements.BringIntoView(new Rect(0, height - 1, width, 1));

解决方案

I think you need to call BringIntoView on the item container, not the ItemsControl itself :

var container = DocumentElements.ItemContainerGenerator.ContainerFromItem(model) as FrameworkElement;
if (container != null)
    container.BringIntoView();

---

EDIT: actually this doesn't work, because at this point, the item container hasn't been generated yet... You could probably handle the StatusChanged event of the ItemContainerGenerator. I tried the following code :

public static class ItemsControlExtensions
{
    public static void BringItemIntoView(this ItemsControl itemsControl, object item)
    {
        var generator = itemsControl.ItemContainerGenerator;

        if (!TryBringContainerIntoView(generator, item))
        {
            EventHandler handler = null;
            handler = (sender, e) =>
            {
                switch (generator.Status)
                {
                    case GeneratorStatus.ContainersGenerated:
                        TryBringContainerIntoView(generator, item);
                        break;
                    case GeneratorStatus.Error:
                        generator.StatusChanged -= handler;
                        break;
                    case GeneratorStatus.GeneratingContainers:
                        return;
                    case GeneratorStatus.NotStarted:
                        return;
                    default:
                        break;
                }
            };

            generator.StatusChanged += handler;
        }
    }

    private static bool TryBringContainerIntoView(ItemContainerGenerator generator, object item)
    {
        var container = generator.ContainerFromItem(item) as FrameworkElement;
        if (container != null)
        {
            container.BringIntoView();
            return true;
        }
        return false;
    }
}

However it doesn't work either... for some reason, ContainerFromItem still returns null after the status changes to ContainersGenerated, and I have no idea why :S

---

EDIT : OK, I understand now... this was because of the virtualization : the containers are generated only when they need to be displayed, so no containers are generated for hidden items. If you switch virtualization off for the ItemsControl (VirtualizingStackPanel.IsVirtualizing="False"), the solution above works fine.

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