c# - 在运行时更改 xamarin.forms 颜色

Question

我正在使用 xamarin.forms 制作一个应用程序，我已经设置了一个配色方案，我希望能够在设置中将其更改为深色风格或浅色风格，现在一切正常，除了我必须重新启动每次我选择不同的配色方案后，该应用程序。

这是我试图在运行时更改它的地方

   private void DarkThemeClick(object sender, EventArgs e)
    {
        database.DropTable(new StyleModel());
        database.CreateTable(new StyleModel());
        database.SaveItem(new StyleModel() { ThemeNum = 1 });
        App.ActiveStyle = new DarkStyle();
    }

    private void LightThemeClick(object sender, EventArgs e)
    {
        database.DropTable(new StyleModel());
        database.CreateTable(new StyleModel());
        database.SaveItem(new StyleModel() { ThemeNum = 0 });
        App.ActiveStyle = new LightStyle();
    }

这是我正在使用的一个项目的示例，我想更改其上的颜色

    using System;
using TestXamForms.Style;
using Xamarin.Forms;

namespace TestXamForms.Helpers
{
class EntryValueCell : StackLayout
{

    public EntryValueCell(string key,int FieldIdx, string value = "",  bool isNumber = false)
    {
        Entry entry;
        Label label = new Label()
        {
            TextColor = App.ActiveStyle.LabelTextColor,
            Text = key,
            HorizontalOptions = LayoutOptions.End
        };
        if (isNumber)
        {
            entry = new Entry()
            {
                ClassId = FieldIdx.ToString(),
                TextColor = App.ActiveStyle.LabelTextColor,
                HorizontalOptions = LayoutOptions.FillAndExpand,
                Keyboard = Keyboard.Numeric,
                Text = value, 


            };
        }
        else
        {
            entry = new Entry()
            {
                ClassId = FieldIdx.ToString(),
                TextColor = App.ActiveStyle.LabelTextColor,
                HorizontalOptions = LayoutOptions.FillAndExpand,
                Keyboard = Keyboard.Text,
                Text = value
            };
        }

        BackgroundColor = App.ActiveStyle.StackLayoutBackground;
        Orientation = StackOrientation.Horizontal;
        VerticalOptions = LayoutOptions.FillAndExpand;
        Children.Add(label);
        Children.Add(entry);
    }
}
}

这是其中一种配色方案的示例

    using Xamarin.Forms;

   namespace TestXamForms.Style
 {
     public  class LightStyle : StyleBase
    {
       public LightStyle()
        {
        LabelTextColor = Color.Black;
        ButtonColor = Color.FromHex("337ab7");
        StackLayoutBackground = Color.FromHex("eff0f1");
        InputBackgroundColor = Color.White;
        PlaceHolderColor = Color.Gray;
        TableColor = Color.FromHex("e6e6e6");
        StacklayoutBorderColor = Color.Black;
       }
      }
     }

这里是上面文件继承的styleBase

using TestXamForms.Models;
using Xamarin.Forms;

namespace TestXamForms.Style
{
public class StyleBase : ModelBase
{
    public enum ThemeNum : int
    {
        Light = 0, Dark = 1
    }
    public Color LabelTextColor { get; set; }
    public Color ButtonColor { get; set; }
    public Color StackLayoutBackground { get; set; }
    public Color InputBackgroundColor { get; set; }
    public Color PlaceHolderColor { get; set; }

    public Color StacklayoutBorderColor { get; set; }

    public Color TableColor { get; set; }

    public int ThemeNums { get; set; }

}
}

这是 App.cs 文件的一部分，它在应用程序启动时加载配色方案

    static StyleBase activeStyle { get; set; }


    public static StyleBase ActiveStyle
    {
        get
        {
            if (activeStyle == null)
            {
                StyleModel styleBase = database.GetItems(new     StyleModel()).First();
                if (styleBase == null)
                {
                    database.SaveItem(new StyleModel() { ThemeNum = 0 }); //sets the default color scheme to light style 
                    styleBase = database.GetItems(new StyleModel()).First();
                }
                int themeNum = styleBase.ThemeNum;
                switch (themeNum)
                {
                    case (int)StyleBase.ThemeNum.Dark:
                        activeStyle = new DarkStyle();
                        break;
                    case (int)StyleBase.ThemeNum.Light:
                        activeStyle = new LightStyle();
                        break;
                }
            }
            return activeStyle;
        }
        set { } }

Answer 1

看看这个blog post .特别是关于 DynamicResources 和 Styles 的部分。

<Application
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    x:Class="Your.App">
    <Application.Resources>
        <ResourceDictionary>
            <Color x:Key="backgroundColor">#33302E</Color>
            <Color x:Key="textColor">White</Color>
        </ResourceDictionary>
    </Application.Resources>
</Application>

现在设置你的资源

<Label Text="{Binding Name}" FontSize="Medium" FontAttributes = "Bold" TextColor = "{DynamicResource textColor}" LineBreakMode="NoWrap"/>
<Label Text="{Binding Text}" FontSize="Small" LineBreakMode="WordWrap" TextColor = "{DynamicResource textColor}"/>

现在您可以在代码中即时更改您的资源

App.Current.Resources ["backgroundColor"] = Color.White;
App.Current.Resources ["textColor"] = Color.Black;

如果您使用的是 2.3，您还可以尝试 built in themes