Xamarin 样式不适用于自定义视图 主页我的视图我的框架更新

如何解决Xamarin 样式不适用于自定义视图 主页我的视图我的框架更新

我创建了一个自定义的 Frame 和 View。我将 Frame 中的 View 和 Page 与 Style 资源相结合，如下所示。

主页

<ContentPage.Resources>
    <Style x:Key="Style" targettype="local:MyFrame">
        <Setter Property="HorizontalOptions" Value="FillAndExpand" />
        <Setter Property="BackgroundColor" Value="LimeGreen" />
    </Style>
</ContentPage.Resources>
<local:MyView>
    <local:MyView.Views>
        <local:MyFrame Style="{StaticResource Style}"
                        HorizontalOptions="FillAndExpand"
                        Title="Number one" />
    </local:MyView.Views>
</local:MyView>

我的视图

public class MyView : ContentView
{
    private readonly StackLayout _layout;
    public ObservableCollection<View> Views { get; set; }

    public MyView()
    {
        Views = new ObservableCollection<View>();
        Views.CollectionChanged += OnViewsCollectionChanged;

        _layout = new StackLayout();
        Content = _layout;
    }

    private void OnViewsCollectionChanged(object sender,NotifyCollectionChangedEventArgs e)
    {
        if (e.OldItems != null)
            foreach (View view in e.OldItems)
                _layout.Children.Remove(view);

        if (e.NewItems != null)
            foreach (View view in e.NewItems)
                _layout.Children.Add(view);
    }
}

我的框架

public class MyFrame : Frame
{
    private readonly Label _title;
    public string Title { set => _title.Text = value; }

    public MyFrame()
    {
        BackgroundColor = Color.LightPink;

        _title = new Label
        {
            TextColor = Color.Black,FontSize = 16,};

         Content = _title;
    }
}

我期望在 MyFrame 背景上使用 LimeGreen 颜色，因为我在 MyFrame.Style 中设置了 MainPage，但实际结果是 LightPink。

我猜在 BackgroundColor 构造函数中设置 MyFrame 并不是要设置默认值。那么如何为 BackgroundColor 设置默认 MyFrame？

我将实际项目简化为可复制的小型项目。这是Github

---

更新

注释掉 BackgroundColor = Color.LightPink; 代码，结果是 LimeGreen 颜色... 那么我如何设置默认的 MyFrame.BackgroundColor？

解决方法

我可以重现您的问题，我可以建议对您的代码进行以下修改，以便能够为您的 MyFrame 视图设置默认背景颜色：

对 MyFrame 的修改

为了解决您的问题，我将 MyFrame 修改为在 Xaml 中定义：

MyFrameXaml.xaml

<?xml version="1.0" encoding="UTF-8"?>
<Frame xmlns="http://xamarin.com/schemas/2014/forms" 
       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
       x:Class="StyleDoesNotApply.MyFrameXAML"
       BackgroundColor="{Binding MyBackgroundColor}">
    <Label x:Name="title"
           TextColor="Black"
           FontSize="16"/>
</Frame>

然后，在后面的代码中定义 MyBackgroundColor 属性如下：

MyFrameXaml.xaml.cs

using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace StyleDoesNotApply
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class MyFrameXAML : Frame
    {

        public string Title { set => title.Text = value; }


        public static readonly BindableProperty MyBackgroundColorProperty =
            BindableProperty.Create(nameof(MyBackgroundColor),typeof(Color),typeof(MyFrame),Color.LightPink);

        public Color MyBackgroundColor
        {
            get => (Color)GetValue(MyBackgroundColorProperty);
            set => SetValue(MyBackgroundColorProperty,value);
        }


        public MyFrameXAML()
        {

            BindingContext = this;
            InitializeComponent();
            
        }
    }
}

使用新视图

<ContentPage.Resources>
    <Style x:Key="Style" TargetType="local:MyFrameXAML">
        <Setter Property="HorizontalOptions" Value="StartAndExpand" />
        <Setter Property="MyBackgroundColor" Value="LimeGreen" />
    </Style>
</ContentPage.Resources>

<StackLayout>
    <Label Text="Style does apply!"
           FontSize="Title"
           TextColor="Black"/>
    <local:MyView>
        <local:MyView.Views>
            <local:MyFrameXAML Style="{StaticResource Style}"
                               HorizontalOptions="FillAndExpand"
                               Title="Number one" />
        </local:MyView.Views>
    </local:MyView>

</StackLayout>

---

更新

可重用代码

public static BindableProperty Override(
    this BindableProperty bindableProperty,string propertyName = null,Type returnType = null,Type declaringType = null,object defaultValue = null,BindingMode defaultBindingMode = BindingMode.OneWay,BindableProperty.ValidateValueDelegate validateValue = null,BindableProperty.BindingPropertyChangedDelegate propertyChanged = null,BindableProperty.BindingPropertyChangingDelegate propertyChanging = null,BindableProperty.CoerceValueDelegate coerceValue = null,BindableProperty.CreateDefaultValueDelegate defaultValueCreator = null)
{
    if (string.IsNullOrEmpty(propertyName))
        propertyName = bindableProperty.PropertyName;
    if (returnType == null)
        returnType = bindableProperty.ReturnType;
    if (declaringType == null)
        declaringType = bindableProperty.DeclaringType;
    if (defaultValue == null)
        defaultValue = bindableProperty.DefaultValue;

    if (propertyChanged == null)
        propertyChanged = (bindable,oldValue,newValue) =>
        {
            var property = bindableProperty.DeclaringType.GetProperty(bindableProperty.PropertyName);
            property.SetValue(bindable,newValue);
        };

    return BindableProperty.Create(propertyName,returnType,declaringType,defaultValue,defaultBindingMode,validateValue,propertyChanged,propertyChanging,coerceValue,defaultValueCreator);
}

public class MyFrame : Frame
{
    // override existing BindableProperty
    public static new readonly BindableProperty BackgroundColorProperty = VisualElement.BackgroundColorProperty.Override();

    private readonly Label _title;
    public string Title { set => _title.Text = value; }

    public MyFrame()
    {
        BackgroundColor = Color.LightPink;

        _title = new Label
        {
            TextColor = Color.Black,FontSize = 16,};

         Content = _title;
    }
}