WPF中TreeView.BringIntoView方法的替代方案

原文:WPF中TreeView.BringIntoView方法的替代方案

WPF中TreeView.BringIntoView方法的替代方案

周银辉

WPF中TreeView.BringIntoView（）方法并不是那么地好用，不少时候会没有效果，这里有一个替代方案，调用SelectItem（）方法可以展开并呈现TreeView上指定的Item：

public static class TreeViewHelper

{

/// <summary>

/// Expands all children of a TreeView

/// </summary>

/// <param name="treeView">The TreeView whose children will be expanded</param>

public static void ExpandAll(this TreeView treeView)

{

ExpandSubContainers(treeView);

}

/// <summary>

/// Expands all children of a TreeView or TreeViewItem

/// </summary>

/// <param name="parentContainer">The TreeView or TreeViewItem containing the children to expand</param>

private static void ExpandSubContainers(ItemsControl parentContainer)

{

foreach (Object item in parentContainer.Items)

{

TreeViewItem currentContainer = parentContainer.ItemContainerGenerator.ContainerFromItem(item) as TreeViewItem;

if (currentContainer != null && currentContainer.Items.Count > 0)

{

//expand the item

currentContainer.IsExpanded = true;

//if the item's children are not generated, they must be expanded

if (currentContainer.ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)

{

//store the event handler in a variable so we can remove it (in the handler itself)

EventHandler eh = null;

eh = new EventHandler(delegate

{

//once the children have been generated, expand those children's children then remove the event handler

if (currentContainer.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)

{

ExpandSubContainers(currentContainer);

currentContainer.ItemContainerGenerator.StatusChanged -= eh;

}

});

currentContainer.ItemContainerGenerator.StatusChanged += eh;

}

else //otherwise the children have already been generated, so we can now expand those children

{

ExpandSubContainers(currentContainer);

}

}

}

}

/// <summary>

/// Searches a TreeView for the provided object and selects it if found

/// </summary>

/// <param name="treeView">The TreeView containing the item</param>

/// <param name="item">The item to search and select</param>

public static void SelectItem(this TreeView treeView, object item)

{

ExpandAndSelectItem(treeView, item);

}

/// <summary>

/// Finds the provided object in an ItemsControl's children and selects it

/// </summary>

/// <param name="parentContainer">The parent container whose children will be searched for the selected item</param>

/// <param name="itemToSelect">The item to select</param>

/// <returns>True if the item is found and selected, false otherwise</returns>

private static bool ExpandAndSelectItem(ItemsControl parentContainer, object itemToSelect)

{

//check all items at the current level

foreach (Object item in parentContainer.Items)

{

TreeViewItem currentContainer = parentContainer.ItemContainerGenerator.ContainerFromItem(item) as TreeViewItem;

//if the data item matches the item we want to select, set the corresponding

//TreeViewItem IsSelected to true

if (item == itemToSelect && currentContainer != null)

{

currentContainer.IsSelected = true;

currentContainer.BringIntoView();

currentContainer.Focus();

//the item was found

return true;

}

}

//if we get to this point, the selected item was not found at the current level, so we must check the children

foreach (Object item in parentContainer.Items)

{

TreeViewItem currentContainer = parentContainer.ItemContainerGenerator.ContainerFromItem(item) as TreeViewItem;

//if children exist

if (currentContainer != null && currentContainer.Items.Count > 0)

{

//keep track of if the TreeViewItem was expanded or not

bool wasExpanded = currentContainer.IsExpanded;

//expand the current TreeViewItem so we can check its child TreeViewItems

currentContainer.IsExpanded = true;

//if the TreeViewItem child containers have not been generated, we must listen to

//the StatusChanged event until they are

if (currentContainer.ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)

{

//store the event handler in a variable so we can remove it (in the handler itself)

EventHandler eh = null;

eh = new EventHandler(delegate

{

if (currentContainer.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)

{

if (ExpandAndSelectItem(currentContainer, itemToSelect) == false)

{

//The assumption is that code executing in this EventHandler is the result of the parent not

//being expanded since the containers were not generated.

//since the itemToSelect was not found in the children, collapse the parent since it was previously collapsed

currentContainer.IsExpanded = false;

}

//remove the StatusChanged event handler since we just handled it (we only needed it once)

currentContainer.ItemContainerGenerator.StatusChanged -= eh;

}

});

currentContainer.ItemContainerGenerator.StatusChanged += eh;

}

else //otherwise the containers have been generated, so look for item to select in the children

{

if (ExpandAndSelectItem(currentContainer, itemToSelect) == false)

{

//restore the current TreeViewItem's expanded state

currentContainer.IsExpanded = wasExpanded;

}

else //otherwise the node was found and selected, so return true

{

return true;

}

}

}

}

//no item was found

return false;

}

}