使用 Rx 進行上下文菜單操作

Question

我想我會嘗試使用新的 System.Reactive 位，看看它是否會簡化響應上下文菜單單擊 ListView 中的項目時執行的操作。 到目前為止，所有設置位似乎都更容易一些，但我正在努力以正確的方式組合兩個事件流（項目選擇和菜單單擊）。

這是我到目前為止所擁有的（bookListView 包含我的書，並顯示菜單 bookListContextMenu）

private void frmBookList_Load(object sender, EventArgs e)
{
    //filter click events to right clicks over a ListViewItem containing a actual book
    var rightclicks = from click in Observable.FromEventPattern<MouseEventArgs>(bookListView, "MouseClick")
                      where click.EventArgs.Button == MouseButtons.Right &&
                      ClickedOnBook((ListView)click.Sender, click.EventArgs) != null
                      select click;

    //subscribe to clicks to display context menu at clicked location
    rightclicks.Subscribe(click => bookListContextMenu.Show((Control)click.Sender, click.EventArgs.Location));
    //subscribe to clicks again to convert click into clicked book
    var rightclickedbook = rightclicks.Select(click => ClickedOnBook((ListView)click.Sender, click.EventArgs));

    //capture context menu click, convert to action enum
    var clickaction = Observable.FromEventPattern<ToolStripItemClickedEventArgs>(bookListContextMenu, "ItemClicked")
                          .Select(click => GetAction(click.EventArgs.ClickedItem));

    //combine the two event streams to get a pair of Book and Action
    //can project to an anonymoue type as it will be consumed within this method
    var bookaction = clickaction.CombineLatest(rightclickedbook, (action, book) => new { Action = action, Book = book });

    //subscribe to action and branch to action specific method
    bookaction.Subscribe(doaction =>
    {
        switch (doaction.Action)
        {
            case BookAction.Delete:
                DeleteBookCommand(doaction.Book);
                break;
            case BookAction.Edit:
                EditBookCommand(doaction.Book);
                break;
        }
    });
}

public enum BookAction
{
    None = 0,
    Edit = 1,
    Delete = 2
}

private BookAction GetAction(ToolStripItem item)
{
    if (item == deleteBookToolStripMenuItem) return BookAction.Delete;
    else if (item == editBookToolStripMenuItem) return BookAction.Edit;
    else return BookAction.None;
}

private Book ClickedOnBook(ListView lview, MouseEventArgs click)
{
    ListViewItem lvitem = lview.GetItemAt(click.X, click.Y);
    return lvitem != null ? lvitem.Tag as Book : null;
}

private void DeleteBookCommand(Book selectedbook)
{
   //code to delete a book
}

private void EditBookCommand(Book selectedbook)
{
   //code to edit a book
}

問題是結合 function。 如果我使用“CombineLatest”，那么在第一次使用上下文菜單之后，每個后續的右鍵單擊都會在新選擇上再次調用上一個操作。

如果我使用“Zip”然后右鍵單擊一本書，但單擊遠離上下文菜單而不是單擊它，那么下次我右鍵單擊並實際單擊菜單時，將在第一次選擇時調用該操作，而不是第二個。

我嘗試了各種 forms 的時間限制緩沖區和 windows 和最新等，但通常只在菜單出現時成功阻止，因此無法選擇，或者如果顯示菜單但沒有項目，則獲得關於空序列的異常被點擊。

我確信一定有一種更簡單的方法可以做到這一點，但我不確定它是什么。

也許這個？

//the menu may be closed with or without clicking any item
var contextMenuClosed = Observable.FromEventPattern(bookListContextMenu, "Closed");
var contextMenuClicked = Observable.FromEventPattern<ToolStripItemClickedEventArgs>(bookListContextMenu, "ItemClicked");

//combine the two event streams to get a pair of Book and Action
//which we can project to an anonymoue type as it will be consumed within this method
var bookaction = from mouseclick in rightclicks
                 let book = ClickedOnBook((ListView)mouseclick.Sender, mouseclick.EventArgs)
                 from menuclick in contextMenuClicked.Take(1).TakeUntil(contextMenuClosed)
                 let action = GetAction(menuclick.EventArgs.ClickedItem)
                 select new { Action = action, Book = book };

Answer 1

解決這些問題的最簡單方法是在整個可觀察序列中攜帶導致元素（從 ClickedOnBook 獲得的元素）。 一種方法是在每次有人單擊圖書時創建上下文菜單的單獨實例。 就像是

IObservable<BookAction> WhenBookAction()
{
    return Observable.Defer(() => 
    {
       var menu = ContextMenuFactory.CreateMenu;
       return Observable
         .FromEventPattern<ToolStripItemClickedEventArgs>(
            menu, "ItemClicked")
         .Select(click => GetAction(click.EventArgs.ClickedItem));
    }
}

現在一個簡單的“來自/來自”就可以了：

from book in rightclicks.Select(
  click => ClickedOnBook((ListView)click.Sender, click.EventArgs))
from action in WhenBookAction()
select book, action;

您可以保證這對中的書正是導致菜單出現的那本書 - “來自/來自” AKA “SelectMany” AKA “Monad” 負責這一點。

編輯：這是另一種不錯的方法。 我懶得復制上下文菜單，所以我的“測試套件”是一個 window，帶有三個名為“firstBn”、“secondBn”和“actionBn”的按鈕——這與這個問題中的模式相同。 這是我得到的：

    public MainWindow()
    {
        InitializeComponent();
        var actions = Observable
            .FromEventPattern<RoutedEventArgs>(actionBn, "Click");
        var firsts = Observable
            .FromEventPattern<RoutedEventArgs>(firstBn, "Click")
            .Select(x => firstBn);
        var seconds = Observable
            .FromEventPattern<RoutedEventArgs>(secondBn, "Click")
            .Select(x => secondBn);
        var buttons = firsts.Merge(seconds);
        var buttonActions = buttons
            .Select(x => actions.Select(_ => x))
            .Switch();
        buttonActions.Subscribe(x => Console.WriteLine(x.Name));
    }