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에서 재평가, 나는 MVVM 패턴 사용자 간의 공통의 문제를 보이는 없애려고 해요.WPF MVVM 명령 CanExecute는 만 WPF</strong><strong>에 <strong>MVVM</strong> 프로젝트를 리팩토링 포커스 변경
보기가 있는데 누가 입니다. DataContext은 입니다. MyViewModel입니다. 다음은 Execute와 CanExecute를 구현하는 Command로 묶인 버튼입니다.
XAML :
<Button Command="{Binding ConnectCommand}"/>
MyViewModel이 ConnectCommand를 노출 :
public ICommand ConnectCommand
{
get { return new DelegateCommand(() => Connect(),() => IsConnectEnabled); }
}
MyViewMo을 (끝 DelegateCommand의 정의는 내가 사용하고 있습니다) 클래스는 가의 인터페이스
public class MyViewModel : INotifyPropertyChanged
{
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
#region rest of the class
}
CanExecute 부분에서 INotifyPropertyChanged 구현
public bool IsConnectEnabled
{
get
{
return (isDisconnected && null!=selectedDevice && 0<selectedDevice.Length);
}
}
MyViewModel : 델는 명령의 CanExecute 부분에 사용 이을 IsConnectEnabled 속성을 노출합니다 명령은 응용 프로그램의 포커스 변경시에만 평가됩니다 (즉, 클릭 할 때마다). UpdateSourceTrigger은 기본적으로 으로 설정되어 있습니다. 따라서 PropertyChanged, 현재 해결책은 PropertyChanged 이벤트를 코드의 몇 군데에 수동으로 발생시키는 것입니다. 그러나 나는 더 잘하고 싶다. IsConnectEnabled 값이 변경 될 때마다이 작업을 자동으로 수행하고 싶다.
WPF와 MVVM 패턴이이 문제에 대한 해결책을 제공합니까?
/// <summary>
/// This class allows delegating the commanding logic to methods passed as parameters,
/// and enables a View to bind commands to objects that are not part of the element tree.
/// </summary>
public class DelegateCommand : ICommand
{
/// <summary>
/// Constructor
/// </summary>
public DelegateCommand(Action executeMethod)
: this(executeMethod, null, false)
{
}
/// <summary>
/// Constructor
/// </summary>
public DelegateCommand(Action executeMethod, Func<bool> canExecuteMethod)
: this(executeMethod, canExecuteMethod, false)
{
}
/// <summary>
/// Constructor
/// </summary>
public DelegateCommand(Action executeMethod, Func<bool> canExecuteMethod, bool isAutomaticRequeryDisabled)
{
if (executeMethod == null)
{
throw new ArgumentNullException("executeMethod");
}
_executeMethod = executeMethod;
_canExecuteMethod = canExecuteMethod;
_isAutomaticRequeryDisabled = isAutomaticRequeryDisabled;
}
#region Public Methods
/// <summary>
/// Method to determine if the command can be executed
/// </summary>
public bool CanExecute()
{
if (_canExecuteMethod != null)
{
return _canExecuteMethod();
}
return true;
}
/// <summary>
/// Execution of the command
/// </summary>
public void Execute()
{
if (_executeMethod != null)
{
_executeMethod();
}
}
/// <summary>
/// Property to enable or disable CommandManager's automatic requery on this command
/// </summary>
public bool IsAutomaticRequeryDisabled
{
get
{
return _isAutomaticRequeryDisabled;
}
set
{
if (_isAutomaticRequeryDisabled != value)
{
if (value)
{
CommandManagerHelper.RemoveHandlersFromRequerySuggested(_canExecuteChangedHandlers);
}
else
{
CommandManagerHelper.AddHandlersToRequerySuggested(_canExecuteChangedHandlers);
}
_isAutomaticRequeryDisabled = value;
}
}
}
/// <summary>
/// Raises the CanExecuteChaged event
/// </summary>
public void RaiseCanExecuteChanged()
{
OnCanExecuteChanged();
}
/// <summary>
/// Protected virtual method to raise CanExecuteChanged event
/// </summary>
protected virtual void OnCanExecuteChanged()
{
CommandManagerHelper.CallWeakReferenceHandlers(_canExecuteChangedHandlers);
}
#endregion
#region ICommand Members
/// <summary>
/// ICommand.CanExecuteChanged implementation
/// </summary>
public event EventHandler CanExecuteChanged
{
add
{
if (!_isAutomaticRequeryDisabled)
{
CommandManager.RequerySuggested += value;
}
CommandManagerHelper.AddWeakReferenceHandler(ref _canExecuteChangedHandlers, value, 2);
}
remove
{
if (!_isAutomaticRequeryDisabled)
{
CommandManager.RequerySuggested -= value;
}
CommandManagerHelper.RemoveWeakReferenceHandler(_canExecuteChangedHandlers, value);
}
}
bool ICommand.CanExecute(object parameter)
{
return CanExecute();
}
void ICommand.Execute(object parameter)
{
Execute();
}
#endregion
#region Data
private readonly Action _executeMethod = null;
private readonly Func<bool> _canExecuteMethod = null;
private bool _isAutomaticRequeryDisabled = false;
private List<WeakReference> _canExecuteChangedHandlers;
#endregion
}
/// <summary>
/// This class allows delegating the commanding logic to methods passed as parameters,
/// and enables a View to bind commands to objects that are not part of the element tree.
/// </summary>
/// <typeparam name="T">Type of the parameter passed to the delegates</typeparam>
public class DelegateCommand<T> : ICommand
{
#region Constructors
/// <summary>
/// Constructor
/// </summary>
public DelegateCommand(Action<T> executeMethod)
: this(executeMethod, null, false)
{
}
/// <summary>
/// Constructor
/// </summary>
public DelegateCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod)
: this(executeMethod, canExecuteMethod, false)
{
}
/// <summary>
/// Constructor
/// </summary>
public DelegateCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod, bool isAutomaticRequeryDisabled)
{
if (executeMethod == null)
{
throw new ArgumentNullException("executeMethod");
}
_executeMethod = executeMethod;
_canExecuteMethod = canExecuteMethod;
_isAutomaticRequeryDisabled = isAutomaticRequeryDisabled;
}
#endregion
#region Public Methods
/// <summary>
/// Method to determine if the command can be executed
/// </summary>
public bool CanExecute(T parameter)
{
if (_canExecuteMethod != null)
{
return _canExecuteMethod(parameter);
}
return true;
}
/// <summary>
/// Execution of the command
/// </summary>
public void Execute(T parameter)
{
if (_executeMethod != null)
{
_executeMethod(parameter);
}
}
/// <summary>
/// Raises the CanExecuteChaged event
/// </summary>
public void RaiseCanExecuteChanged()
{
OnCanExecuteChanged();
}
/// <summary>
/// Protected virtual method to raise CanExecuteChanged event
/// </summary>
protected virtual void OnCanExecuteChanged()
{
CommandManagerHelper.CallWeakReferenceHandlers(_canExecuteChangedHandlers);
}
/// <summary>
/// Property to enable or disable CommandManager's automatic requery on this command
/// </summary>
public bool IsAutomaticRequeryDisabled
{
get
{
return _isAutomaticRequeryDisabled;
}
set
{
if (_isAutomaticRequeryDisabled != value)
{
if (value)
{
CommandManagerHelper.RemoveHandlersFromRequerySuggested(_canExecuteChangedHandlers);
}
else
{
CommandManagerHelper.AddHandlersToRequerySuggested(_canExecuteChangedHandlers);
}
_isAutomaticRequeryDisabled = value;
}
}
}
#endregion
#region ICommand Members
/// <summary>
/// ICommand.CanExecuteChanged implementation
/// </summary>
public event EventHandler CanExecuteChanged
{
add
{
if (!_isAutomaticRequeryDisabled)
{
CommandManager.RequerySuggested += value;
}
CommandManagerHelper.AddWeakReferenceHandler(ref _canExecuteChangedHandlers, value, 2);
}
remove
{
if (!_isAutomaticRequeryDisabled)
{
CommandManager.RequerySuggested -= value;
}
CommandManagerHelper.RemoveWeakReferenceHandler(_canExecuteChangedHandlers, value);
}
}
bool ICommand.CanExecute(object parameter)
{
// if T is of value type and the parameter is not
// set yet, then return false if CanExecute delegate
// exists, else return true
if (parameter == null &&
typeof(T).IsValueType)
{
return (_canExecuteMethod == null);
}
return CanExecute((T)parameter);
}
void ICommand.Execute(object parameter)
{
Execute((T)parameter);
}
#endregion
#region Data
private readonly Action<T> _executeMethod = null;
private readonly Func<T, bool> _canExecuteMethod = null;
private bool _isAutomaticRequeryDisabled = false;
private List<WeakReference> _canExecuteChangedHandlers;
#endregion
}
/// <summary>
/// This class contains methods for the CommandManager that help avoid memory leaks by
/// using weak references.
/// </summary>
internal class CommandManagerHelper
{
internal static void CallWeakReferenceHandlers(List<WeakReference> handlers)
{
if (handlers != null)
{
// Take a snapshot of the handlers before we call out to them since the handlers
// could cause the array to me modified while we are reading it.
EventHandler[] callees = new EventHandler[handlers.Count];
int count = 0;
for (int i = handlers.Count - 1; i >= 0; i--)
{
WeakReference reference = handlers[i];
EventHandler handler = reference.Target as EventHandler;
if (handler == null)
{
// Clean up old handlers that have been collected
handlers.RemoveAt(i);
}
else
{
callees[count] = handler;
count++;
}
}
// Call the handlers that we snapshotted
for (int i = 0; i < count; i++)
{
EventHandler handler = callees[i];
handler(null, EventArgs.Empty);
}
}
}
internal static void AddHandlersToRequerySuggested(List<WeakReference> handlers)
{
if (handlers != null)
{
foreach (WeakReference handlerRef in handlers)
{
EventHandler handler = handlerRef.Target as EventHandler;
if (handler != null)
{
CommandManager.RequerySuggested += handler;
}
}
}
}
internal static void RemoveHandlersFromRequerySuggested(List<WeakReference> handlers)
{
if (handlers != null)
{
foreach (WeakReference handlerRef in handlers)
{
EventHandler handler = handlerRef.Target as EventHandler;
if (handler != null)
{
CommandManager.RequerySuggested -= handler;
}
}
}
}
internal static void AddWeakReferenceHandler(ref List<WeakReference> handlers, EventHandler handler)
{
AddWeakReferenceHandler(ref handlers, handler, -1);
}
internal static void AddWeakReferenceHandler(ref List<WeakReference> handlers, EventHandler handler, int defaultListSize)
{
if (handlers == null)
{
handlers = (defaultListSize > 0 ? new List<WeakReference>(defaultListSize) : new List<WeakReference>());
}
handlers.Add(new WeakReference(handler));
}
internal static void RemoveWeakReferenceHandler(List<WeakReference> handlers, EventHandler handler)
{
if (handlers != null)
{
for (int i = handlers.Count - 1; i >= 0; i--)
{
WeakReference reference = handlers[i];
EventHandler existingHandler = reference.Target as EventHandler;
if ((existingHandler == null) || (existingHandler == handler))
{
// Clean up old handlers that have been collected
// in addition to the handler that is to be removed.
handlers.RemoveAt(i);
}
}
}
}
}
}
WPF 또는 Silverlight? – heltonbiker
@heltonbiker WPF. 감사합니다. 설명에서 더 명확하게했습니다. – Riccardo
"WPF와 MVVM 패턴이이 문제를 해결할 수 있습니까?" 아니. – Will