如何在xamarin表单中更改Picker Border颜色

Question

我的无边框自定义渲染器

public class BorderlessPickerRenderer : PickerRenderer
    {
        public static void Init() { }
        protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
        {
            base.OnElementChanged(e);
            if (e.OldElement == null)
            {
                Control.Background = null;
            }
        }
    }

它会将选取器列表文本颜色更改为白色。请参阅屏幕截图

Answer 1

如果您查看PickerRenderer的源代码，您会发现后面的代码中完全生成了Dialog。

所以在这里设置Transparent（无边框）背景，我们可以重新编写此控件的Click事件，例如：

public class BorderlessPickerRenderer : Xamarin.Forms.Platform.Android.PickerRenderer
{
    private IElementController ElementController => Element as IElementController;
    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())
        {
            picker.MaxValue = model.Items.Count - 1;
            picker.MinValue = 0;
            picker.SetDisplayedValues(model.Items.ToArray());
            picker.WrapSelectorWheel = false;
            picker.DescendantFocusability = DescendantFocusability.BlockDescendants;
            picker.Value = model.SelectedIndex;
        }

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

        ElementController.SetValueFromRenderer(VisualElement.IsFocusedPropertyKey, true);

        var builder = new AlertDialog.Builder(Context);
        builder.SetView(layout);
        builder.SetTitle(model.Title ?? "");
        builder.SetNegativeButton(global::Android.Resource.String.Cancel, (s, a) =>
        {
            ElementController.SetValueFromRenderer(VisualElement.IsFocusedPropertyKey, 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(global::Android.Resource.String.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.IsFocusedPropertyKey, 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.IsFocusedPropertyKey, false);
        };
        _dialog.Show();
        _dialog.Window.SetBackgroundDrawable(new ColorDrawable(Android.Graphics.Color.Transparent));
    }
}

渲染此自定义选择器的图像：

由于您自己创建了此对话框，因此可以根据需要修改字体颜色和按钮的样式。对话框的样式也取决于应用程序的样式。