[Silverlight] 改进 Nikhil Kothari 的换肤方案：允许自定义控件的皮肤定义

在 Silverlight 下换肤的实现 中，我介绍了 Nikhil Kothari 实现的一种 Theme 方案。但是实践了一下，我很快发现有个小小的缺陷。作者的皮肤定义是仅针对系统自带的控件的，如 Button, TextBox, CheckBox 等，而对于我们自定义的控件的换肤问题没有很好的解决。从下列代码中可见一斑：

(/Framework/Applications/Theme.cs)

public string GetXml() {
    string resourceDictionaryFormat =
@"<UserControl 
xmlns=""http://schemas.microsoft.com/winfx/2006/xaml/presentation""
xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml""
xmlns:vsm=""clr-namespace:System.Windows;assembly=System.Windows"">
<UserControl.Resources>
{0}
</UserControl.Resources>
</UserControl>";

    _content.Replace(@"xmlns=""http://schemas.microsoft.com/winfx/2006/xaml/presentation""", "");
    _content.Replace(@"xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml""", "");
    _content.Replace(@"xmlns:vsm=""clr-namespace:System.Windows;assembly=System.Windows""", "");

    return String.Format(resourceDictionaryFormat, _content.ToString());
 }

可以看出这里名称空间都是写死了的，不支持任何扩展。
而实际使用中，我们可能会对某个第三方控件定义样式。比如：

<UserControl
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:liquid="clr-namespace:Liquid;assembly=Liquid"
    mc:Ignorable="d"
    x:Class="UserControl"
    d:DesignWidth="640" d:DesignHeight="480">
    <UserControl.Resources>
        <Style x:Key="MyLiquidDialog" TargetType="liquid:Dialog">
            <!-- 略 -->
        </Style>    
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White" />
</UserControl>

这里定义了 Liquid 这套组件中 Dialog 控件的样式，而其中 xmlns:liquid 这个名称空间的声明就是必须的。

要达到这个目标，我们可以修改 Theme.cs 的 parse 步骤，在其过程中补充一段收集 xml namespace 的代码，并在合并最终的样式 xaml 时加进去即可。

修改过的 Theme.cs 代码如下：

修改过的 Theme.cs
// Theme.cs
// Copyright (c) Nikhil Kothari, 2008. All Rights Reserved.
// http://www.nikhilk.net
//
// This product's copyrights are licensed under the Creative
// Commons Attribution-ShareAlike (version 2.5).B
// http://creativecommons.org/licenses/by-sa/2.5/
//
// You are free to:
// - use this framework as part of your app
// - make use of the framework in a commercial app
// as long as your app or product is itself not a framework, control pack or
// developer toolkit of any sort under the following conditions:
// Attribution. You must attribute the original work in your
//              product or release.
// Share Alike. If you alter, transform, or build as-is upon this work,
//              you may only distribute the resulting app source under
//              a license identical to this one.
//

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Windows;
using System.Windows.Browser;
using System.Windows.Controls;
using System.Windows.Markup;
using System.Windows.Resources;
using System.Xml;

namespace Silverlight.FX.Applications
{

    /// <summary>
    /// Represents a theme control, whose top-level resource items are to be included
    /// when this theme is selected.
    /// </summary>
    public class Theme : UserControl
    {

        private string _includes;

        /// <summary>
        /// Any additional themes to include. Each of the additional themes must contain
        /// a UserControl declaration. The list of themes are processed in order after
        /// the current theme's resource items have been included.
        /// </summary>
        public string Includes
        {
            get
            {
                return _includes ?? String.Empty;
            }
            set
            {
                _includes = value;
            }
        }

        private static void ExtractThemeContent(string xml, ThemeInfo theme, bool extractIncludes)
        {
            XmlReader xmlReader = XmlReader.Create(
                new StringReader(xml),
                new XmlReaderSettings
                {
                   CheckCharacters = false,
                   DtdProcessing = DtdProcessing.Ignore,
                   IgnoreComments = true,
                   IgnoreProcessingInstructions = true,
                   IgnoreWhitespace = true,
                });
            while (xmlReader.Read())
            {
                if (xmlReader.NodeType == XmlNodeType.Element)
                {
                    // Found the first element

                    // 保存元素节点名称，因为下面要跳到属性去读取
                    var elementName = xmlReader.Name;

                    if (extractIncludes)
                    {
                        theme.Includes = xmlReader.GetAttribute("Includes");
                    }

                    // 添加名称空间
                    var hasAttr = xmlReader.MoveToFirstAttribute();
                    if (hasAttr)
                    {
                        do
                        {
                            if (xmlReader.Name.StartsWith("xmlns:"))
                            {
                                var val = xmlReader.ReadContentAsString();
                                theme.AddNamespace(xmlReader.Name, val);
                            }
                        } while (xmlReader.MoveToNextAttribute());
                    }


                    string resourcesTag = elementName + ".Resources";

                    // 改为由父节点属性读到指定名称的子节点. 不能用 ReadToDescendant.
                    if (xmlReader.ReadToFollowing(resourcesTag))
                    {
                        //if (xmlReader.ReadToDescendant(resourcesTag)) {
                        xmlReader.MoveToContent();

                        // TODO: I would have expected MoveToContent to move to the first item
                        //       within the current tag, but apparently the reader is still
                        //       positioned at the current tag, unless a Read is performed.
                        xmlReader.Read();

                        while (xmlReader.EOF == false)
                        {
                            if (xmlReader.NodeType == XmlNodeType.Element)
                            {
                                string key = xmlReader.GetAttribute("x:Key");
                                if ((String.IsNullOrEmpty(key) == false) && (theme.ContainsKey(key) == false))
                                {
                                    string markup = xmlReader.ReadOuterXml();
                                    theme.AddItem(key, markup);
                                }
                                else
                                {
                                    xmlReader.Skip();
                                }
                            }
                            else
                            {
                                // No more items
                                break;
                            }
                        }
                    }

                    // We only look at the resources of the root tag, and so we're done
                    break;
                }
            }
        }

        private static string GetThemeXaml(string themeName, string fileName, bool lookupShared)
        {
            StreamResourceInfo resourceInfo = null;

            // First try /Themes/<ThemeName>/<FileName>.xaml
            Uri resourceUri = new Uri("Themes/" + themeName + "/" + fileName + ".xaml", UriKind.Relative);
            resourceInfo = Application.GetResourceStream(resourceUri);

            if ((resourceInfo == null) && lookupShared)
            {
                // The fallback is one level up, i.e. /Themes/<FileName>.xaml
                resourceUri = new Uri("Themes/" + fileName + ".xaml", UriKind.Relative);
                resourceInfo = Application.GetResourceStream(resourceUri);
            }

            if (resourceInfo == null)
            {
                throw new InvalidOperationException("The file named '" + fileName + " in the theme named '" + themeName + "' could not be found.");
            }

            StreamReader resourceReader = new StreamReader(resourceInfo.Stream);
            return resourceReader.ReadToEnd();
        }

        internal static void LoadTheme(ResourceDictionary targetResources, string name)
        {
            ThemeInfo theme = new ThemeInfo();

            string themeXaml = GetThemeXaml(name, "Theme", /* lookupShared */ false);
            try
            {
                ExtractThemeContent(themeXaml, theme, /* extractIncludes */ true);
                if ((theme.Includes.Length == 0) && (theme.Keys.Count != 0))
                {
                    UserControl userControl = (UserControl)XamlReader.Load(themeXaml);
                    ResourceDictionary themeResources = userControl.Resources;

                    foreach (string key in theme.Keys)
                    {
                        targetResources.Add(key, themeResources[key]);
                    }

                    return;
                }
            }
            catch (Exception e)
            {
                throw new InvalidOperationException("The theme named '" + name + "' contained invalid XAML.", e);
            }

            if (theme.Includes.Length != 0)
            {
                string[] includes = theme.Includes.Split(new char[] { ',', ' ' }, StringSplitOptions.RemoveEmptyEntries);

                for (int i = 0; i < includes.Length; i++)
                {
                    string includeXaml = GetThemeXaml(name, includes[i], /* lookupShared */ true);
                    try
                    {
                        ExtractThemeContent(includeXaml, theme, /* extractIncludes */ false);
                    }
                    catch (Exception e)
                    {
                        throw new InvalidOperationException("The include named '" + includes[i] + "' in the theme named '" + name + "' contained invalid XAML.", e);
                    }
                }
            }

            try
            {
                string mergedXaml = theme.GetXml();
                UserControl userControl = (UserControl)XamlReader.Load(mergedXaml);
                ResourceDictionary themeResources = userControl.Resources;

                foreach (string key in theme.Keys)
                {
                    targetResources.Add(key, themeResources[key]);
                }
            }
            catch (Exception e)
            {
                throw new InvalidOperationException("The theme named '" + name + "' contained invalid XAML.", e);
            }
        }


        private sealed class ThemeInfo
        {

            private StringBuilder _content;
            private List<string> _keys;
            private Dictionary<string, string> _keyMap;
            private string _includes;

            public ThemeInfo()
            {
                _content = new StringBuilder();
                _keys = new List<string>();
                _keyMap = new Dictionary<string, string>();

                InitXmlNamespaces();
            }

            public string Includes
            {
                get
                {
                    return _includes ?? String.Empty;
                }
                set
                {
                    _includes = value;
                }
            }

            public ICollection<string> Keys
            {
                get
                {
                    return _keys;
                }
            }

            public void AddItem(string key, string xml)
            {
                _keyMap[key] = String.Empty;
                _keys.Add(key);

                _content.Append(xml);
            }

            public bool ContainsKey(string key)
            {
                return _keyMap.ContainsKey(key);
            }

            // 增加自定义名称空间的功能
            private Dictionary<string, string> _xmlNamespaces;

            // 初始化名称空间字典
            private void InitXmlNamespaces()
            {
                _xmlNamespaces = new Dictionary<string, string>();
                _xmlNamespaces["xmlns"] = "http://schemas.microsoft.com/winfx/2006/xaml/presentation";
                _xmlNamespaces["xmlns:x"] = "http://schemas.microsoft.com/winfx/2006/xaml";
                _xmlNamespaces["xmlns:vsm"] = "clr-namespace:System.Windows;assembly=System.Windows";
            }

            // 组合名称空间属性
            private string GetNamespaceAttributes()
            {
                var sb = new StringBuilder();
                foreach (var pair in _xmlNamespaces)
                {
                    sb.AppendFormat("\n  {0}=\"{1}\"", pair.Key, pair.Value);
                }
                return sb.ToString();
            }

            // 替换掉内容中的名称空间
            private void ReplaceContent()
            {
                foreach (var pair in _xmlNamespaces)
                {
                    _content.Replace(pair.Key + "=\"" + pair.Value + "\"", "");
                }
            }

            /// <summary>
            /// 添加名称空间
            /// </summary>
            /// <returns></returns>
            public void AddNamespace(string key, string value)
            {
                // 不覆盖已有的名称
                if (_xmlNamespaces.ContainsKey(key))
                    return;
                _xmlNamespaces[key] = value;
            }

            public string GetXml()
            {
                string resourceDictionaryFormat =
@"<UserControl {0}>
  <UserControl.Resources>
{1}
  </UserControl.Resources>
</UserControl>";

                ReplaceContent();

                return String.Format(resourceDictionaryFormat,
                    GetNamespaceAttributes(),
                    _content.ToString());
            }
        }
    }
}

其中灰色部分是主要修改的代码。这样改过后，重新编译 Nikhil Kothari 的 Framework 项目，并把生成的 dll 引用到自己项目中即可支持第三方控件的换肤了。

修改过的 DLL [下载]