动态加载与插件系统的初步实现（3）：WinForm示例

动态加载与插件系统的初步实现（三）：WinForm示例

代码文件在此Download，本文章围绕前文所述默认AppDomain、插件容器AppDomain两个域及IPlugin、PluginProvider、PluginProxy3个类的使用与变化进行。



添加WinForm项目Host、类库Plugin、引用System.Windows.Forms;的类库Plugin_A与Plugin_B，其中Plugin_A、Plugin_B的项目属性中，“生成”选项卡中“输出路径”设置为..\Host\bin\Debug\，即指向Host项目的Bin目录。



考虑到WinForm项目常常涉及多级菜单构建，这里以两级菜单示例。

Plugin项目中IPlugin代码：

public interface IPlugin
{
IList<String> GetMenus();
IList<String> GetMenus(String menu);
void Notify(Object userState);
}

其中无参方法GetMenus()提取一级菜单，有参重载GetMenus(String menu)提取二级菜单，Notify(Object userState)是两个应用程序域的通知调用。

PluginProxy继承MarshalByRefObject，代码长点：

public class PluginProxy : MarshalByRefObject, IDisposable
{
private readonly static PluginProxy instance = new PluginProxy();

public static PluginProxy Instance
{
get { return instance; }
}

private PluginProxy()
{
}

private AppDomain hostDomain = null;
private PluginProvider proxy = null;

public PluginProvider Proxy
{
get
{
if (hostDomain == null)
{
hostDomain = AppDomain.CreateDomain("PluginHost");
}
if (proxy == null)
{
Type proxyType = typeof(PluginProvider);
proxy = (PluginProvider)hostDomain.CreateInstanceAndUnwrap(proxyType.Assembly.FullName, proxyType.FullName);
}
return proxy;
}
}

public void Unload()
{
if (hostDomain != null)
{
proxy = null;
AppDomain.Unload(hostDomain);
hostDomain = null;
}
}

public void Dispose()
{
Unload();
}
}

PluginProvider除构造函数外，Notify(IPlugin plugin, Object userState)方法将调用IPlugin插件的Notify方法：

public class PluginProvider : MarshalByRefObject
{
[ImportMany]
public IEnumerable<Lazy<IPlugin>> Plugins { get; set; }

public PluginProvider()
{
AggregateCatalog catalog = new AggregateCatalog();
catalog.Catalogs.Add(new DirectoryCatalog("."));
CompositionContainer container = new CompositionContainer(catalog);
container.ComposeParts(this);
}

public void Notify(IPlugin plugin, Object userState)
{
plugin.Notify(userState);
}
}

然后是插件Plugin_A、Plugin_B的实现。添加Plugin类（类名与命名空间随意）引用System.ComponentModel.Composition，加入[Export(typeof(IPlugin))]修饰。这里使用了一份XML显示菜单目录，将在得到通知后将一个Form弹出来：

[Export(typeof(IPlugin))]
public class PluginA : MarshalByRefObject, IPlugin
{
private String menus =
@"<Component>
<Net>
<AuthenticationManager />
<Authorization />
<Cookie />
</Net>
<IO>
<ErrorEventArgs />
<FileSystemEventArgs />
</IO>
</Component>";

public IList<String> GetMenus()
{
return XElement.Parse(menus).Elements().Select(x => x.Name.LocalName).ToArray();
}

public IList<String> GetMenus(String menu)
{
return XElement.Parse(menus).Elements(menu).Elements().Select(x => x.Name.LocalName).ToArray();
}

public void Notify(Object userState)
{
String text = (String)userState;
Label label = new Label()
{
Text = text,
AutoSize = false,
Dock = DockStyle.Fill,
TextAlign = System.Drawing.ContentAlignment.MiddleCenter,
};
Form frm = new Form();
frm.Controls.Add(label);
frm.ShowDialog();
}
}

Plugin_B与Plugin_A类似，不再重复，然后是Host实现。Host使用了两个FlowLayoutPanel分别用于显示一级菜单与两级菜单。



Load按钮加载插件列表，将每个插件绑定到一个Button上：

private void button1_Click(object sender, EventArgs e)
{
flowLayoutPanel1.Controls.Clear();
textBox1.AppendText("PluginProvider loaded");
textBox1.AppendText(Environment.NewLine);

PluginProvider proxy = PluginProxy.Instance.Proxy;

IEnumerable<Lazy<IPlugin>> plugins = proxy.Plugins;
foreach (var plugin in plugins)
{
foreach (var menu in plugin.Value.GetMenus())
{
Button menuBtn = new Button();
menuBtn.Text = menu;
menuBtn.Tag = plugin.Value;
menuBtn.Click += menuBtn_Click;
flowLayoutPanel1.Controls.Add(menuBtn);
}
}
}

private void menuBtn_Click(object sender, EventArgs e)
{
flowLayoutPanel2.Controls.Clear();
Button menuBtn = (Button)sender;

try
{
IPlugin plugin = (IPlugin)menuBtn.Tag;
foreach (var item in plugin.GetMenus(menuBtn.Text))
{
Button itemBtn = new Button();
itemBtn.Text = item;
itemBtn.Tag = plugin;
itemBtn.Click += itemBtn_Click;
flowLayoutPanel2.Controls.Add(itemBtn);
}
}
catch (AppDomainUnloadedException)
{
textBox1.AppendText("Plugin domain have been uloaded");
textBox1.AppendText(Environment.NewLine);
}
}

private void itemBtn_Click(object sender, EventArgs e)
{
try
{
Button menuBtn = (Button)sender;
IPlugin plugin = (IPlugin)menuBtn.Tag;
PluginProvider proxy = PluginProxy.Instance.Proxy;
proxy.Notify(plugin, menuBtn.Text);
}
catch (AppDomainUnloadedException)
{
textBox1.AppendText("Plugin domain not loaded");
textBox1.AppendText(Environment.NewLine);
}
}

Unload按钮卸载插件AppDomain：

private void button2_Click(object sender, EventArgs e)
{
PluginProxy.Instance.Unload();
textBox1.AppendText("PluginProvider unloaded");
textBox1.AppendText(Environment.NewLine);
}

Delete按钮移除Plugin_A.dll、Plugin_B.dll：

private void button3_Click(object sender, EventArgs e)
{
try
{
String[] pluginPaths = new[] { "Plugin_A.dll", "Plugin_B.dll" };
foreach (var item in pluginPaths)
{
if (System.IO.File.Exists(item))
{
System.IO.File.Delete(item);
textBox1.AppendText(item + " deleted");
}
else
{
textBox1.AppendText(item + " not exist");
}
textBox1.AppendText(Environment.NewLine);
}
}
catch (Exception ex)
{
textBox1.AppendText(ex.Message);
textBox1.AppendText(Environment.NewLine);
}
}

运行结果如下：



我尝试比较IEnumerable<Lazy<IPlugin>>与IEnumerable<IPlugin>的进程内存占用，在一个额外的Button里进行100加载与卸载，统计内存变化图如下，有兴趣的可以下载EXCEL文件看看：