自定义Xamarin.Forms选择器弹出列表

Question

我知道如何创建自定义渲染器以自定义Xamarin表单选择器的实际文本，但是如何自定义，例如单击选择器文本框时弹出的列表的背景颜色或文本？

Answer 1

您可以参考以下代码：

在iOS中

using System;
using Xamarin.Forms;
using xxx;
using xxx.iOS;
using UIKit;
using Xamarin.Forms.Platform.iOS;
using Foundation;

[assembly:ExportRenderer(typeof(MyPicker), typeof(MyiOSPicker))]
namespace xxx.iOS
{
    public class MyiOSPicker:PickerRenderer,IUIPickerViewDelegate
    {

      IElementController ElementController => Element as IElementController;

      public MyiOSPicker()
      {

      }

      [Export("pickerView:viewForRow:forComponent:reusingView:")]
      public UIView GetView(UIPickerView pickerView, nint row, nint component, UIView view)
      {

         UILabel label = new UILabel
         {
            //here you can set the style of item!!!

            TextColor = UIColor.Blue,

            Text = Element.Items[(int)row].ToString(),

            TextAlignment = UITextAlignment.Center,

         };
         return label;
      }


      protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
      {
        base.OnElementChanged(e);

        if(Control!=null)
        {
            UIPickerView pickerView = (UIPickerView)Control.InputView;
            pickerView.WeakDelegate = this;
            pickerView.BackgroundColor = UIColor.Yellow; //set the background color of pickerview

        }


      }


    }
}

在Android中

using System;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
using xxx;
using xxx.Droid;
using Android.Widget;
using Android.App;
using System.Linq;

[assembly: ExportRenderer(typeof(MyPicker), typeof(MyAndroidPicker))]
namespace xxx.Droid
{
    public class MyAndroidPicker:PickerRenderer
    {

      IElementController ElementController => Element as IElementController;

      public MyAndroidPicker()
      {

      }


      private AlertDialog _dialog;

      protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
      {
        base.OnElementChanged(e);

        if (e.NewElement == null || e.OldElement != null)
            return;

        Control.Click += Control_Click;
      }

      protected override void Dispose(bool disposing)
      {
        Control.Click -= Control_Click;
        base.Dispose(disposing);
      }

      private void Control_Click(object sender, EventArgs e)
      {
        Picker model = Element;

        var picker = new NumberPicker(Context);
        if (model.Items != null && model.Items.Any())
        {
            // set style here
            picker.MaxValue = model.Items.Count - 1;
            picker.MinValue = 0;
            picker.SetBackgroundColor(Android.Graphics.Color.Yellow);
            picker.SetDisplayedValues(model.Items.ToArray());
            picker.WrapSelectorWheel = false;
            picker.Value = model.SelectedIndex;
        }

        var layout = new LinearLayout(Context) { Orientation = Orientation.Vertical };
        layout.AddView(picker);

        ElementController.SetValueFromRenderer(VisualElement.IsFocusedProperty, true);

        var builder = new AlertDialog.Builder(Context);
        builder.SetView(layout);

        builder.SetTitle(model.Title ?? "");
        builder.SetNegativeButton("Cancel  ", (s, a) =>
        {
            ElementController.SetValueFromRenderer(VisualElement.IsFocusedProperty, false);
            // It is possible for the Content of the Page to be changed when Focus is changed.
            // In this case, we'll lose our Control.
            Control?.ClearFocus();
            _dialog = null;
        });
        builder.SetPositiveButton("Ok ", (s, a) =>
        {
            ElementController.SetValueFromRenderer(Picker.SelectedIndexProperty, picker.Value);
            // It is possible for the Content of the Page to be changed on SelectedIndexChanged.
            // In this case, the Element & Control will no longer exist.
            if (Element != null)
            {
                if (model.Items.Count > 0 && Element.SelectedIndex >= 0)
                    Control.Text = model.Items[Element.SelectedIndex];
                ElementController.SetValueFromRenderer(VisualElement.IsFocusedProperty, false);
                // It is also possible for the Content of the Page to be changed when Focus is changed.
                // In this case, we'll lose our Control.
                Control?.ClearFocus();
            }
            _dialog = null;
        });

        _dialog = builder.Create();
        _dialog.DismissEvent += (ssender, args) =>
        {
            ElementController?.SetValueFromRenderer(VisualElement.IsFocusedProperty, false);
        };
        _dialog.Show();
      }

    }
}