修改 TextBox 上下文菜单/MenuFlyout

Question

我尝试使用此代码修改 TextBox 上下文菜单/MenuFlyout，但它不起作用（额外的菜单项不出现，myFlyout 总是 null）（UWP/C#）

        private void Menu_Opening(object sender, object e)
        {
            MenuFlyout myFlyout = sender as MenuFlyout;
            if (myFlyout != null && myFlyout.Target == TextBox)
            {
                MenuFlyoutSubItem searchWith = new MenuFlyoutSubItem();
                searchWith.Icon = new SymbolIcon(Symbol.Find);
                searchWith.Text = "Search With";
                MenuFlyoutItem googles = new MenuFlyoutItem();
                googles.Text = "Google";
                googles.Click += Googles_Click;
                searchWith.Items.Add(googles);
                MenuFlyoutItem bings = new MenuFlyoutItem();
                bings.Text = "Bing";
                bings.Click += Bings_Click;
                searchWith.Items.Add(bings);
                myFlyout.Items.Add(searchWith);
            }
        }

        private async void Googles_Click(object sender, RoutedEventArgs e)
        {
            if (TextBox.SelectedText != null)
            {
                var uri= new Uri(@"https://google.com/search?q=" + TextBox.SelectedText);
                var success = await Launcher.LaunchUriAsync(uri);
            }
        }

        private async void Bings_Click(object sender, RoutedEventArgs e)
        {
            if (TextBox.SelectedText != null)
            {
                var uri = new Uri(@"https://bing.com/search?q=" + TextBox.SelectedText);
                var success = await Launcher.LaunchUriAsync(uri);
            }
        }

        private void TextBox_Loaded(object sender, RoutedEventArgs e)
        {
            TextBox.SelectionFlyout.Opening += Menu_Opening;
            TextBox.ContextFlyout.Opening += Menu_Opening;
        }

        private void TextBox_Unloaded(object sender, RoutedEventArgs e)
        {
            TextBox.SelectionFlyout.Opening -= Menu_Opening;
            TextBox.ContextFlyout.Opening -= Menu_Opening;
        }

<TextBox x:Name="TextBox" Loaded="TextBox_Loaded" Unloaded="TextBox_Unloaded"/>                        

Answer 1

问题是您没有将MenuFlyout 实例提供给SelectionFlyout 或ContextFlyout。请参考以下代码添加MenuFlyout。

<TextBox x:Name="TextBox" Loaded="TextBox_Loaded" Unloaded="TextBox_Unloaded">
    <TextBox.ContextFlyout>
        <MenuFlyout>
        </MenuFlyout>
    </TextBox.ContextFlyout>
</TextBox>

更新

SelectionFlyout的默认类型是TextCommandBarFlyout，如果你不想替换默认类型，它不能转换为MenuFlyout。你可以像下面这样添加TextCommandBarFlyout，

private void Menu_Opening(object sender, object e)
{
    TextCommandBarFlyout myFlyout = sender as TextCommandBarFlyout;

    if (myFlyout != null && myFlyout.Target == TextBox)
    {
        AppBarButton searchCommandBar = new AppBarButton() { Icon = new SymbolIcon(Symbol.Find), Label = "Search With" };
        searchCommandBar.Click += SearchCommandBar_Click;
        myFlyout.PrimaryCommands.Add(searchCommandBar);

    }
}

private void SearchCommandBar_Click(object sender, RoutedEventArgs e)
{

}