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Is Using Custom Delegates in an ICommand Implementation the Best Approach for Avoiding Repeated Instantiation?
Is Using Custom Delegates in an ICommand Implementation the Best Approach for Avoiding Repeated Instantiation?
Jan 20, 2025 pm 05:21 PM
ICommand implementation in MVVM: avoid repeated instantiation
Question:
To avoid repeatedly creating ICommand instances, I tried to implement an ICommand class using a custom delegate. This class contains two delegates: OnExecute (void delegate, accepts object parameters) and OnCanExecute (bool delegate, accepts object parameters).
The code is as follows:
public class TestCommand : ICommand
{
public delegate void ICommandOnExecute(object parameter);
public delegate bool ICommandOnCanExecute(object parameter);
private ICommandOnExecute _execute;
private ICommandOnCanExecute _canExecute;
public TestCommand(ICommandOnExecute onExecuteMethod, ICommandOnCanExecute onCanExecuteMethod)
{
_execute = onExecuteMethod;
_canExecute = onCanExecuteMethod;
}
//...
}
This approach works, but I have doubts about the plausibility of its implementation and whether there is a better way.
Solution:
This approach is very similar to the commonly used RelayCommand pattern, RelayCommand is a more mature and optimized solution.
RelayCommand implementation:
public class RelayCommand : ICommand
{
private readonly Predicate<object> _canExecute;
private readonly Action<object> _execute;
public RelayCommand(Predicate<object> canExecute, Action<object> execute)
{
_canExecute = canExecute;
_execute = execute;
}
//...
}
Usage:
public class MyViewModel
{
private RelayCommand _doSomething;
public ICommand DoSomethingCommand
{
get
{
return _doSomething ??= new RelayCommand(
p => this.CanDoSomething(),
p => this.DoSomeImportantMethod());
}
}
}
Use null-coalescing assignment (??=) to ensure that RelayCommand instances are only created once.
Reference:
By using RelayCommand or a similar pre-built implementation, you can avoid the additional complexity of custom delegates and get cleaner, more reliable code.
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