PDFOffice_Windows_exe/PDF Office/Views/PageEdit/PageEditContent.xaml.cs

using PDF_Office.EventAggregators;
using PDF_Office.Tools;
using Prism.Events;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Threading;

namespace PDF_Office.Views.PageEdit
{
    /// <summary>
    /// PageEditContent.xaml 的交互逻辑
    /// </summary>
    public partial class PageEditContent : UserControl
    {
        /// <summary>
        /// 用于通知刷新图片的事件
        /// 因为目前的图片刷新策略依赖很多UI事件判断，因为将主要判断逻辑放在UI层，VM负责图片刷新，非必要情况尽量不要采用这种形式
        /// </summary>
        private IEventAggregator eventor;

        /// <summary>
        /// 暂存的唯一索引值,用于区分多页签
        /// </summary>
        private string unicode;

        /// <summary>
        /// 是否是加载时第一次触发滚动
        /// </summary>
        private bool isFirstScrollChange = true;

        /// <summary>
        /// 用于判断滚轮停止的计时器
        /// </summary>
        private DispatcherTimer timer = new DispatcherTimer();

        /// <summary>
        /// 记录当前滑块的状态
        /// </summary>
        private ScrollEventType scrolltype = ScrollEventType.EndScroll;

        public PageEditContent()
        {
            InitializeComponent();
        }


        public PageEditContent(IEventAggregator eventAggregator) :this()
        {
            eventor = eventAggregator;
            unicode = App.mainWindowViewModel.SelectedItem.Unicode;

            timer.Interval = TimeSpan.FromSeconds(0.3);
            timer.Tick += Timer_Tick;
        }

        private void Timer_Tick(object sender, EventArgs e)
        {
            PulishEvent();
            timer.Stop();
        }


        /// <summary>
        /// 每次显示的时候就触发事件，刷新所有图片
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void PageEdit_IsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
        {
            if((bool)e.NewValue)
            {
                PulishEvent();
            }
        }

        /// <summary>
        /// 发布事件
        /// </summary>
        private void PulishEvent()
        {
            var range = GetRoughFromView(ListPageEdit, new Size(208, 320), new Thickness(5, 10, 5, 10));
            eventor.GetEvent<PageEditRefreshEvent>().Publish(new PageEditRefreshEventArgs() { Unicode = unicode, PageRange = range });
        }

        /// <summary>
        /// 获取滑轨的垂直偏移量，结合item总数和Item尺寸以及间隔，来估算实际展示的item范围
        /// 返回值为页面范围  从1开始
        /// </summary>
        /// <param name="view"></param>
        /// <param name="itemSize"></param>
        /// <param name="itemMargin"></param>
        /// <returns></returns>
        private Tuple<int, int, int> GetRoughFromView(ListBox view, Size itemSize, Thickness itemMargin)
        {
            //var scrollViewer = GetScrollHost(view);
            var scrollViewer = CommonHelper.FindVisualChild<ScrollViewer>(view);
            if (scrollViewer == null || scrollViewer.ActualHeight == 0 || scrollViewer.ActualWidth == 0)//视图展开
                return new Tuple<int, int, int>(0, 0, 0);
            try
            {
                var currentHeight = scrollViewer.ActualHeight - view.Padding.Top;
                var currentWidth = scrollViewer.ActualWidth;
                //计算当前窗口大小能显示的行数和列数
                var columnCount = (int)(currentWidth / (itemSize.Width + itemMargin.Left));
                var rowCount = (int)Math.Ceiling(currentHeight / (itemSize.Height + itemMargin.Bottom));

                var preItemCount = (int)((scrollViewer.VerticalOffset / scrollViewer.ExtentHeight) * ((view.Items.Count + columnCount - 1) / columnCount));//滑动百分比*行数 = 大概的垂直位置
                preItemCount = preItemCount * columnCount;
                var preEnd = (int)(((scrollViewer.VerticalOffset + scrollViewer.ActualHeight) / scrollViewer.ExtentHeight) * ((view.Items.Count + columnCount - 1) / columnCount));
                preEnd = preEnd * columnCount + columnCount - 1;

                var middle = (int)Math.Ceiling(preItemCount + preEnd / 2d);

                return new Tuple<int, int, int>(
                    Math.Max(preItemCount, 0),
                    Math.Min(view.Items.Count, preEnd),
                    middle);
            }
            catch (Exception ex)
            {

            }
            return new Tuple<int, int, int>(0, 0, 0);
        }

        /// <summary>
        /// 获取listbox里的ScrollViewer对象
        /// 留意如果有重写ListBox对象,该方法可能无效
        /// </summary>
        /// <param name="listBox"></param>
        /// <returns></returns>
        private ScrollViewer GetScrollHost(ListBox listBox)
        {
            if (VisualTreeHelper.GetChildrenCount(listBox) > 0)
            {
                int s = VisualTreeHelper.GetChildrenCount(listBox);

                Border border = VisualTreeHelper.GetChild(listBox, 0) as Border;
                if (border != null)
                {
                    return VisualTreeHelper.GetChild(border, 0) as ScrollViewer;
                }
            }
            return null;
        }

        private void ListPageEdit_ScrollChanged(object sender, ScrollChangedEventArgs e)
        {
            if (isFirstScrollChange)
            {
                PulishEvent();//第一次加载时触发的Scollchange 直接刷新界面，减少白板显示时间
                isFirstScrollChange = false;
                return;
            }
            else
            {
                if (e.VerticalChange != 0)
                    timer.Start();//暂时找不到比较好的 判断Scroller停止的方法，先用计时器粗略判断
            }
        }

        private void ListPageEdit_Scroll(object sender, System.Windows.Controls.Primitives.ScrollEventArgs e)
        {
            scrolltype = e.ScrollEventType;
            if (scrolltype != System.Windows.Controls.Primitives.ScrollEventType.EndScroll)
            {
                timer.Stop();
                return;
            }
            PulishEvent();
        }
    }
}