ios - 如何在 iOS ViewCellRenderer 中更改 Forms ViewList 的 MenuItem 颜色？

Question

有没有办法更改 Xamarin.Forms Xaml 文件中添加的 ContextAction 菜单的颜色。 IsDestructive="True" 将菜单颜色设置为红色。但我需要另一个看起来像绿色或其他颜色的菜单。

这是我的 Forms Xaml 代码..

<ListView x:Name="planList" ItemsSource="{x:Static local:SampleData.PLAN_DATA}" RowHeight="150" HorizontalOptions="FillAndExpand">
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <ViewCell.ContextActions>
                    <MenuItem Clicked="OnEditClick" Text="Edit" CommandParameter="{Binding .}"/> <!-- THIS HAS TO BE GREEN COLOR -->
                    <MenuItem Clicked="OnDeleteClick" Text="Delete" IsDestructive="True" />
                </ViewCell.ContextActions>
                <ViewCell.View>
                    <StackLayout Orientation="Vertical"  HorizontalOptions="Start" VerticalOptions="FillAndExpand">
                        <!--Non Editable State-->
                        <StackLayout Orientation="Horizontal" Spacing="28" IsVisible="{Binding isNotSaveState}">
                            <Frame  WidthRequest="130" HeightRequest="50" BackgroundColor="#151617" HorizontalOptions="Start">
                                <Label Text="{Binding from}" TextColor="#ff9600" FontSize="Medium" FontFamily="Helvetica"/>
                            </Frame>
                        </StackLayout>
                        <!--Editable State-->
                        <StackLayout Orientation="Horizontal" Spacing="0"  IsVisible="{Binding isSaveState}">
                            <StackLayout Orientation="Horizontal" Spacing="5">
                                <Label Text="From" TextColor="#838288"  FontSize="Medium" FontFamily="Helvetica"/>
                                <Entry Text="" BackgroundColor="Red"/>
                            </StackLayout>
                            <Button Text="Save" BackgroundColor="Green" CommandParameter="{Binding .}" Clicked="onSaveClick" />
                        </StackLayout>
                    </StackLayout>
                </ViewCell.View>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

这是我的渲染器..

[assembly: ExportRenderer(typeof(MyApp.Views.Cells.CustomViewCell), typeof(MyApp.iOS.Views.Cells.CustomViewCellRenderer))]
namespace MyApp.iOS.Views.Cells
{

    public class CustomViewCellRenderer : ViewCellRenderer
    {
        public override UITableViewCell GetCell(Cell item, UITableViewCell reusableCell, UITableView tv)
        {
            UITableViewCell cell = base.GetCell(item, reusableCell, tv);

            // I have no Idea how to access the Swipe Menus from Renderer

            //cell.EditingAccessory
            //cell.EditingAccessoryView

            return cell;
        }        
    }
}

Answer 1

Xamarin 通过继承 UITableViewCell 的原生单元格 ContextActionsCell 实现上下文菜单。

但是，截至今天的 Xamarin.Forms.Platform.iOS (1.4.0.6340-pre2) 程序集，设置手势和按钮的 ContextActionsCell 仍然是 internal 类，不可访问或继承以更改任何内容。

---

等等!

不过，您可以使用Reflection 来更改上面的internal 内容。

示例:

// Get UIImage with a green color fill
CGRect rect = new CGRect (0, 0, 1, 1);
CGSize size = rect.Size;
UIGraphics.BeginImageContext (size);
CGContext currentContext = UIGraphics.GetCurrentContext ();
currentContext.SetFillColor (0, 1, 0, 1);
currentContext.FillRect (rect);
var backgroundImage = UIGraphics.GetImageFromCurrentImageContext ();
currentContext.Dispose ();

// This is the assembly full name which may vary by the Xamarin.Forms version installed.
// NullReferenceException is raised if the full name is not correct.
var t = Type.GetType("Xamarin.Forms.Platform.iOS.ContextActionsCell, Xamarin.Forms.Platform.iOS, Version=1.3.1.0, Culture=neutral, PublicKeyToken=null");

// Now change the static field value!
var field = t.GetField ("destructiveBackground", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static);
field.SetValue (null, backgroundImage);

注意 1:这将更改所有上下文菜单的破坏性背景颜色。

注意2:如果你也想改变普通颜色，字段名称为normalBackground。

注意 3:Xamarin 可能会将这些类设为内部，目的是 API 和行为在未来可能会发生变化。以上示例可能会在即将发布的版本中中断。