浅析issuevision中的command模式
浅析issuevision中的command模式
在issuevision中有个command设计模式，就像一个指挥官，一声令下，他的士兵们都得听他的命令。
在issuevision中，
Commander又分为ToolbarButtonCommander和MenuItemCommander，即有两个指挥官，一个管toolbar，一个管menu
public class Command
{
// The EnableChanged event is raised when the IsEnabled value of the command
// changes. This is handled in the Commander objects to set the Enabled property
// of the managed controls.命令类，指挥官要下达的命令.这里用代表的方式来解决
public delegate void EnableChangedEventHandler(object sender, Command.EnableChangedEventArgs e);
public virtual event EnableChangedEventHandler EnableChanged;
public delegate void Action();
private Action m_action;
private bool m_isEnabled = true;
// The IsEnabled property is used to set/retrieve the enabled state of all UI
// controls that the command manages 是否可用
public bool IsEnabled
{
get
{
return m_isEnabled;
}
set
{
if (m_isEnabled != value)
{
m_isEnabled = value;
if (EnableChanged != null) //设置是否可用时，触发该事件 {
EnableChanged(this, new EnableChangedEventArgs(IsEnabled));
}
}
}
}
public Command(Action action)
{
m_action = action;
}
// Invokes the method assigned to this command.执行命令
public void Execute()
{
m_action();
}
// Arguments passed to the EnableChanged event.
public class EnableChangedEventArgs : EventArgs
{
private bool m_isEnabled = false;
public bool IsEnabled
{
get
{
return m_isEnabled;
}
}
public EnableChangedEventArgs(bool isEnabled)
{
m_isEnabled = isEnabled;
}
}
}
public abstract class Commander //总指挥官
{
protected Command m_command;
protected abstract void HandleEnableChangedEvent(object sender, Command.EnableChangedEventArgs e);
protected Commander(Command command)
{
m_command = command;
m_command.EnableChanged += new Command.EnableChangedEventHandler(this.HandleEnableChangedEvent);
}
}
// MenuItemCommander类 下属指挥官
public class MenuItemCommander : Commander
{
private MenuItem m_item;
protected MenuItemCommander(MenuItem item, Command command) : base(command)
{
m_item = item;
m_item.Click += new EventHandler(this.HandleUIEvent);
}
protected override void HandleEnableChangedEvent(object sender, Command.EnableChangedEventArgs e)
{
m_item.Enabled = e.IsEnabled;
}
private void HandleUIEvent(object sender, EventArgs e)
{
m_command.Execute();
}
// Connect is a shared (static) method that performs the task of adapting a menu
// item to a command. The commander exists only to wire up the two objects --
// it is not used further
public static void Connect(MenuItem item, Command command) //把士兵管理起来
{
MenuItemCommander unused = new MenuItemCommander(item, command);
}
}
public class ToolBarButtonCommander : Commander //下属指挥官
{
private ToolBarButton m_button;
protected ToolBarButtonCommander(ToolBarButton button, Command command) : base(command)
{
m_button = button;
button.Parent.ButtonClick += new ToolBarButtonClickEventHandler(this.HandleUIEvent);
}
protected override void HandleEnableChangedEvent(object sender, Command.EnableChangedEventArgs e)
{
m_button.Enabled = e.IsEnabled;
}
private void HandleUIEvent(object sender, ToolBarButtonClickEventArgs e)
{
if (m_button == e.Button)
{
m_command.Execute();
}
}
// Connect is a shared (static) method that performs the task of adapting a toolbar
// button to a command. The commander exists only to wire up the two objects --
// it is not used further
public static void Connect(ToolBarButton button, Command command)
{
ToolBarButtonCommander unused = new ToolBarButtonCommander(button, command);
}
}
然后指挥官又下达一系列的命令：
private void InitializeCommands()
{
// Wire up menus and toolbar buttons
//Command pattern: File | Send & Receive
m_sendReceiveCommand = new Command(new Command.Action(this.SendReceive_Action));
//菜单项需要执行这个命令
MenuItemCommander.Connect(menuSendReceive, m_sendReceiveCommand);
//工具栏项需要执行这个命令
ToolBarButtonCommander.Connect(tlbSendReceive, m_sendReceiveCommand);
}
例如这个命令就是让tlbSendRecieve这个士兵去执行m_sendReceiveCommand（发送/接收）的命令，这里命令是由ToolBarButtonCommander下达的
如果我们不用command模式，那么可能就应该这样写：
当菜单项点击时调用SendReceive_Action方法，当工具栏点击时调用SendReceive_Action方法
如果我们系统所有的工具栏改用双击事件了，那么我们再调用SendReceive_Action这个方法时，我们又要修改整个系统了，很麻烦。
而用命令模式，就能很好的解决这个问题，我们只需要改ToolbarButtonCommander中的一个方法就可以了。
只要总的指挥官可以对他下属下达命令，具体的执行就看他的下属怎么做了。这里toolbarButtonCommander和MenuItemCommander就是Commander这个总指挥官的下属。
