如何使用渲染器更改 Android 选项卡的背景颜色，同时使用自定义渲染器添加一些填充

在我的应用程序中，我设置底部标签栏背景颜色，如下所示：

<Shell xmlns="http://xamarin.com/schemas/2014/forms" 
       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
       x:Class="M.Views.AppShell"
       NavBarIsVisible="True"
       xmlns:local="clr-namespace:Memorise"
       BackgroundColor="{DynamicResource ShellBackgroundColor}"
       TabBarBackgroundColor="{DynamicResource TabBarBackgroundColor}" 
       TabBarDisabledColor="{DynamicResource TabBarDisabledColor}" 
       TabBarForegroundColor="{DynamicResource TabBarForegroundColor}" 
       TabBarTitleColor="{DynamicResource TabBarTitleColor}" 
       TabBarUnselectedColor="{DynamicResource TabBarUnselectedColor}"

我创建了一个自定义渲染器来向 Android 上的选项卡添加一些侧边距：

public class CustomShellRenderer : ShellRenderer
{
    public CustomShellRenderer(Context context)
        : base(context)
    {
    }

    protected override IShellBottomNavViewAppearanceTracker CreateBottomNavViewAppearanceTracker(ShellItem shellItem)
    {
        return new MarginedTabBarAppearance();
    }
}

public class MarginedTabBarAppearance : IShellBottomNavViewAppearanceTracker
{
    public void Dispose()
    {
    }

    public void SetAppearance(BottomNavigationView bottomView, IShellAppearanceElement appearance)
    {
        if (App.devWidth == SIZE.L)
            bottomView.SetPadding(400, 0, 400, 0);
    }

    public void ResetAppearance(BottomNavigationView bottomView)
    {
    }
}

不幸的是，这也有一个副作用，它将选项卡的背景颜色设置为白色。

有谁知道我如何使用此渲染器并将背景颜色更改为与 DynamicResource ShellBackgroundColor 相同？

带有渲染器的代码被注释掉：

public class CustomShellRenderer : ShellRenderer
{
    public CustomShellRenderer(Context context)
        : base(context)
    {
    }

    //protected override IShellBottomNavViewAppearanceTracker CreateBottomNavViewAppearanceTracker(ShellItem shellItem)
    //{
    //    return new MarginedTabBarAppearance();
    //}
}

public class MarginedTabBarAppearance : IShellBottomNavViewAppearanceTracker
{
    public void Dispose()
    {
    }

    public void SetAppearance(BottomNavigationView bottomView, IShellAppearanceElement appearance)
    {
        //if (App.devWidth == SIZE.L)
        //    bottomView.SetPadding(400, 0, 400, 0);
        //if (Application.Current.Resources["TabBarBackgroundColor"] is Xamarin.Forms.Color color1)
        //{
        //    bottomView.SetBackgroundColor(color1.ToAndroid());
        //}
    }

    public void ResetAppearance(BottomNavigationView bottomView)
    {
    }
}

带有注释掉的渲染器的选项卡栏：

** 带有渲染器的代码未注释掉：**

public class CustomShellRenderer : ShellRenderer
{
    public CustomShellRenderer(Context context)
        : base(context)
    {
    }

    protected override IShellBottomNavViewAppearanceTracker CreateBottomNavViewAppearanceTracker(ShellItem shellItem)
    {
        return new MarginedTabBarAppearance();
    }
}

public class MarginedTabBarAppearance : IShellBottomNavViewAppearanceTracker
{
    public void Dispose()
    {
    }

    public void SetAppearance(BottomNavigationView bottomView, IShellAppearanceElement appearance)
    {
        if (App.devWidth == SIZE.L)
            bottomView.SetPadding(400, 0, 400, 0);
        if (Application.Current.Resources["TabBarBackgroundColor"] is Xamarin.Forms.Color color1)
        {
            bottomView.SetBackgroundColor(color1.ToAndroid());
        }
    }

    public void ResetAppearance(BottomNavigationView bottomView)
    {
    }
}

带有渲染器的选项卡栏未注释掉：

Mihail 建议的更新代码：

public class MarginedTabBarAppearance :    ShellBottomNavViewAppearanceTracker
{

public MarginedTabBarAppearance(IShellContext shellContext, ShellItem shellItem)
    : base(shellContext, shellItem)
{
}

public override void SetAppearance(BottomNavigationView bottomView, IShellAppearanceElement appearance)
{
    base.SetAppearance(bottomView, appearance);

    bottomView.SetPadding(400, 0, 400, 0);

    if (Application.Current.Resources.ContainsKey("TabBarBackgroundColor") && 
        Application.Current.Resources["TabBarBackgroundColor"] is Color tabColor)
    {
        bottomView.SetBackgroundColor(tabColor.ToAndroid());
    }
}
}

In your SetAppearance方法，您可以像这样设置背景颜色：

bottomView.SetBackgroundColor(Android.Graphics.Color.Red);

但是，那SetBackgroundColor需要类型颜色Android.Graphics.Color我发现你想从 a 中获取颜色动态资源，这将返回一个Xamarin.Forms.Color。好处是这两种颜色类别都很容易转换，所以我们只需要获取当前的颜色类别值动态资源:

if (Application.Current.Resources["CustomTabBackgroundColor"] is Xamarin.Forms.Color color)
{
    bottomView.SetBackgroundColor(color.ToAndroid());
}

Here, CustomTabBackgroundColor是你的颜色的关键color.ToAndroid()执行 2 个类之间的转换（从 Xamarin 到 Android 类）。

UPDATE

由于问题的更新，我将补充一点，在这种情况下，样式/颜色重置的问题不是由于背景更改造成的，而是完全由于其他原因造成的。设置新视图外观的方式（return new MarginedTabBarAppearance();) 重置所有默认样式。由于我们正在实施一切界面并且不是源自基类，我们无法从已经预设的值中获取任何内容。为了解决这个问题，我们需要改变MarginedTabBarAppearance正在实施的类：

public class MarginedTabBarAppearance : ShellBottomNavViewAppearanceTracker
{
    public MarginedTabBarAppearance(IShellContext shellContext, ShellItem shellItem)
        : base(shellContext, shellItem)
    {
    }

    public override void SetAppearance(BottomNavigationView bottomView, IShellAppearanceElement appearance)
    {
        base.SetAppearance(bottomView, appearance);

        bottomView.SetPadding(400, 0, 400, 0);

        if (Application.Current.Resources.ContainsKey("TabBarBackgroundColor") && 
            Application.Current.Resources["TabBarBackgroundColor"] is Color tabColor)
        {
            bottomView.SetBackgroundColor(tabColor.ToAndroid());
        }
    }
}

此外，您还必须更改您的CreateBottomNavViewAppearanceTracker像这样的方法：

protected override IShellBottomNavViewAppearanceTracker CreateBottomNavViewAppearanceTracker(ShellItem shellItem)
{
    return new MarginedTabBarAppearance(this, shellItem);
}

这样，我们将采用我们已经设计好的所有内容，并且只需更改我们需要的内容即可。