c# - 如何在 xamarin 表单中更改选择器底线颜色

Question

我需要更改选择器的底线颜色并更改选择器中显示的项目列表的背景颜色。我可以设置选择器的背景颜色。但是选择器中项目的背景颜色默认为白色。是有任何自定义渲染器或任何其他解决方案吗？我按以下方式在选择器中添加项目。

血型列表显示为白色。我需要更改该颜色。如何设置项目列表背景颜色？

public List<string> _bloodGroups = new List<string>() { "A+ve", "A-ve", "B+ve", "B-Ve", "O+ve", "O-ve", "AB+ve", "AB_ve" };

public void GetDistrictAsync()
{            
    foreach (string districts in _districts)
    {
        Picker_District.Items.Add(districts);
    }
}

在 XAML 页面中，代码如下

<StackLayout Orientation="Horizontal" 
    HorizontalOptions="FillAndExpand" 
    VerticalOptions="FillAndExpand" 
    HeightRequest="10"
    Margin="20,10,20,0"  
    BackgroundColor="#91BC47">
    <Picker 
        x:Name="Picker_BloodGroup" 
        HorizontalOptions="FillAndExpand"  
        TextColor="White" 
        BackgroundColor="#91BC47">
        <Picker.Items>
            <x:String>Select Blood Group</x:String>                           
        </Picker.Items>
    </Picker>
</StackLayout>

Answer 1

你好@jasminemathew 在 xamarin ios 部分添加这个自定义渲染器 记得在命名空间之前添加这一行 [程序集:ExportRenderer(typeof(Picker), typeof(CustomPickerRenderer))]

 public class CustomPickerRenderer : PickerRenderer
{
    private CALayer _borderLayer;
    protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
    {
        base.OnElementChanged(e);

        if (Control == null)
            return;

        Control.BorderStyle = UITextBorderStyle.None;

        var element = Element as Picker;
        if (element == null)
            return;

        //DrawBorder(element.BorderColor.ToCGColor());
        DrawBorder(UIColor.FromRGB(156, 156, 156));

        e.NewElement.Unfocused += (sender, evt) =>
        {
            DrawBorder(UIColor.FromRGB(156, 156, 156)); // unfocused, set color

        };
        e.NewElement.Focused += (sender, evt) =>
        {
            DrawBorder(UIColor.FromRGB(245, 0, 47)); ; // focused, set color
        };
    }
    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);

        var element = Element as Picker;
        if (element == null)
            return;

        DrawBorder(UIColor.FromRGB(156, 156, 156));
    }
    public override CGRect Frame
    {
        get { return base.Frame; }
        set
        {
            base.Frame = value;

            var element = Element as Picker;
            if (element == null)
                return;

            // DrawBorder(element.BorderColor.ToCGColor());
            DrawBorder(UIColor.FromRGB(156, 156, 156));
        }
    }
    private void DrawBorder(UIColor borderColor)
    {
        if (Frame.Height <= 0 || Frame.Width <= 0)
            return;

        if (_borderLayer == null)
        {
            _borderLayer = new CALayer
            {
                MasksToBounds = true,
                Frame = new CGRect(0f, Frame.Height - 1, Frame.Width, 1f),
                BorderColor = borderColor.CGColor,
                BorderWidth = 1.0f
            };

            Control.Layer.AddSublayer(_borderLayer);
            Control.BorderStyle = UITextBorderStyle.None;
        }
        else
        {
            _borderLayer.BorderColor = borderColor.CGColor;
            _borderLayer.Frame = new CGRect(0f, Frame.Height - 1, Frame.Width, 1f);
        }
    }
}.