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9c8afab2ea
Restoring the selection works pretty much like it used to, though I'm capping the total size of the selection because it goes into stupid-slow mode if you have too many elements. Getting the item that is at the top of the ListView is astoundingly obscure, due to the ListView's extreme generality. I make a simplifying assumption -- that we're using a VSP -- which allows us to use a simple vertical offset once we've dug the appropriate object out of the visual tree. (The alternative is to walk through the list of items and see what's on screen, or perform a hit test calculation in the upper left corner.) Yay WPF.
94 lines
3.6 KiB
C#
94 lines
3.6 KiB
C#
/*
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* Copyright 2019 faddenSoft
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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using System;
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using System.Diagnostics;
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using System.Windows;
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using System.Windows.Controls;
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using System.Windows.Media;
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namespace CommonWPF {
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/// <summary>
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/// Generic Visual helper.
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/// </summary>
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public static class VisualHelper {
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/// <summary>
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/// Find a child object in a WPF visual tree.
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/// </summary>
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/// <remarks>
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/// Sample usage:
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/// GridViewHeaderRowPresenter headerRow = listView.GetVisualChild<GridViewHeaderRowPresenter>();
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///
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/// From https://social.msdn.microsoft.com/Forums/vstudio/en-US/7d0626cb-67e8-4a09-a01e-8e56ee7411b2/gridviewcolumheader-radiobuttons?forum=wpf
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/// </remarks>
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/// <typeparam name="T"></typeparam>
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/// <param name="referenceVisual"></param>
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/// <returns></returns>
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public static T GetVisualChild<T>(this Visual referenceVisual) where T : Visual {
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Visual child = null;
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for (Int32 i = 0; i < VisualTreeHelper.GetChildrenCount(referenceVisual); i++) {
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child = VisualTreeHelper.GetChild(referenceVisual, i) as Visual;
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if (child != null && child is T) {
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break;
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} else if (child != null) {
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child = GetVisualChild<T>(child);
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if (child != null && child is T) {
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break;
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}
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}
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}
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return child as T;
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}
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}
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/// <summary>
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/// Add functions to get the element that's currently shown at the top of the ListView
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/// window, and to scroll the list so that a specific item is at the top.
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/// </summary>
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public static class ListViewExtensions {
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/// <summary>
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/// Figures out which item index is at the top of the window. This only works for a
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/// ListView with a VirtualizingStackPanel.
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/// </summary>
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/// <returns>The item index, or -1 if the list is empty.</returns>
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public static int GetTopItemIndex(this ListView lv) {
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if (lv.Items.Count == 0) {
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return -1;
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}
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VirtualizingStackPanel vsp = lv.GetVisualChild<VirtualizingStackPanel>();
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if (vsp == null) {
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Debug.Assert(false, "ListView does not have a VirtualizingStackPanel");
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return -1;
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}
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return (int) vsp.VerticalOffset;
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}
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/// <summary>
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/// Scrolls the ListView so that the specified item is at the top. The standard
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/// ListView.ScrollIntoView() makes the item visible but doesn't ensure a
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/// specific placement.
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/// </summary>
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/// <remarks>
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/// Equivalent to setting myListView.TopItem in WinForms.
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/// </remarks>
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public static void ScrollToTopItem(this ListView lv, object item) {
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ScrollViewer sv = lv.GetVisualChild<ScrollViewer>();
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sv.ScrollToBottom();
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lv.ScrollIntoView(item);
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}
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}
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}
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