Table of Contents

Class ReactiveCommandBase<TParam, TResult>

Namespace
ReactiveUI
Assembly
ReactiveUI.dll

A base class for generic reactive commands.

public abstract class ReactiveCommandBase<TParam, TResult> : IReactiveCommand<TParam, TResult>, IObservable<TResult>, IReactiveCommand, IDisposable, IHandleObservableErrors, ICommand

Type Parameters

TParam

The type of parameter values passed in during command execution.

TResult

The type of the values that are the result of command execution.

Inheritance
ReactiveCommandBase<TParam, TResult>
Implements
IReactiveCommand<TParam, TResult>
IObservable<TResult>
Derived
Extension Methods
WhenAnyMixin.WhenAny<TSender, TRet, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12>(TSender?, Expression<Func<TSender, T1>>, Expression<Func<TSender, T2>>, Expression<Func<TSender, T3>>, Expression<Func<TSender, T4>>, Expression<Func<TSender, T5>>, Expression<Func<TSender, T6>>, Expression<Func<TSender, T7>>, Expression<Func<TSender, T8>>, Expression<Func<TSender, T9>>, Expression<Func<TSender, T10>>, Expression<Func<TSender, T11>>, Expression<Func<TSender, T12>>, Func<IObservedChange<TSender, T1>, IObservedChange<TSender, T2>, IObservedChange<TSender, T3>, IObservedChange<TSender, T4>, IObservedChange<TSender, T5>, IObservedChange<TSender, T6>, IObservedChange<TSender, T7>, IObservedChange<TSender, T8>, IObservedChange<TSender, T9>, IObservedChange<TSender, T10>, IObservedChange<TSender, T11>, IObservedChange<TSender, T12>, TRet>)

Remarks

This class extends ReactiveCommand and adds generic type parameters for the parameter values passed into command execution, and the return values of command execution.

Because the result type is known by this class, it can implement IObservable<T>. However, the implementation is defined as abstract, so subclasses must provide it.

Reactive commands encapsulate the behavior of running some execution logic and then surfacing the results on the UI thread. Importantly, no scheduling is performed against input observables (the canExecute and execution pipelines).

To create an instance of ReactiveCommand, call one of the static creation methods defined by this class. Create(Action, IObservable<bool>?, IScheduler?) can be used when your execution logic is synchronous. ReactiveCommand.CreateFromObservable and ReactiveCommand.CreateFromTask (and overloads) can be used for asynchronous execution logic. Optionally, you can provide an observable that governs the availability of the command for execution, as well as a scheduler to which events will be delivered.

The CanExecute property provides an observable that can be used to determine whether the command is eligible for execution. The value of this observable is determined by both the canExecute observable provided during command creation, and the current execution status of the command. A command that is already executing will yield false from its CanExecute observable regardless of the canExecute observable provided during command creation.

The IsExecuting property provides an observable whose value indicates whether the command is currently executing. This can be a useful means of triggering UI, such as displaying an activity indicator whilst a command is executing.

As discussed above, you are under no obligation to somehow incorporate this into your canExecute observable because that is taken care of for you. That is, if the value of IsExecuting is true, the value of CanExecute will be false. However, if the value of CanExecute is false, that does not imply the value of IsExecuting is true.

Any errors in your command's execution logic (including any canExecute observable you choose to provide) will be surfaced via the ThrownExceptions observable. This gives you the opportunity to handle the error before it triggers a default handler that tears down the application. For example, you might use this as a means of alerting the user that something has gone wrong executing the command.

For the sake of convenience, all ReactiveCommand instances are also implementations of ICommand. This allows you to easily integrate instances of ReactiveCommand into platforms that understands ICommand natively (such as WPF and UWP).

Constructors

ReactiveCommandBase()

protected ReactiveCommandBase()

Properties

CanExecute

Gets an observable whose value indicates whether the command can currently execute.

public abstract IObservable<bool> CanExecute { get; }

Property Value

IObservable<bool>

The can execute.

Remarks

The value provided by this observable is governed both by any canExecute observable provided during command creation, as well as the current execution status of the command. A command that is currently executing will always yield false from this observable, even if the canExecute pipeline is currently true.

IsExecuting

Gets an observable whose value indicates whether the command is currently executing.

public abstract IObservable<bool> IsExecuting { get; }

Property Value

IObservable<bool>

The is executing.

Remarks

This observable can be particularly useful for updating UI, such as showing an activity indicator whilst a command is executing.

ThrownExceptions

Gets a observable which will fire whenever an exception would normally terminate ReactiveUI internal state.

public abstract IObservable<Exception> ThrownExceptions { get; }

Property Value

IObservable<Exception>

Methods

Dispose()

public void Dispose()

Dispose(bool)

Disposes of the managed resources.

protected abstract void Dispose(bool disposing)

Parameters

disposing bool

If its getting called by the Dispose() method.

Execute()

Gets an observable that, when subscribed, executes this command.

public abstract IObservable<TResult> Execute()

Returns

IObservable<TResult>

An observable that will tick the single result value if and when it becomes available.

Remarks

Invoking this method will return a cold (lazy) observable that, when subscribed, will execute the logic encapsulated by the command. It is worth restating that the returned observable is lazy. Nothing will happen if you call Execute and neglect to subscribe (directly or indirectly) to the returned observable.

If no parameter value is provided, a default value of type TParam will be passed into the execution logic.

Any number of subscribers can subscribe to a given execution observable and the execution logic will only run once. That is, the result is broadcast to those subscribers.

In those cases where execution fails, there will be no result value. Instead, the failure will tick through the ThrownExceptions observable.

Execute(TParam)

Gets an observable that, when subscribed, executes this command.

public abstract IObservable<TResult> Execute(TParam parameter)

Parameters

parameter TParam

The parameter to pass into command execution.

Returns

IObservable<TResult>

An observable that will tick the single result value if and when it becomes available.

Remarks

Invoking this method will return a cold (lazy) observable that, when subscribed, will execute the logic encapsulated by the command. It is worth restating that the returned observable is lazy. Nothing will happen if you call Execute and neglect to subscribe (directly or indirectly) to the returned observable.

If no parameter value is provided, a default value of type TParam will be passed into the execution logic.

Any number of subscribers can subscribe to a given execution observable and the execution logic will only run once. That is, the result is broadcast to those subscribers.

In those cases where execution fails, there will be no result value. Instead, the failure will tick through the ThrownExceptions observable.

ICommandCanExecute(object?)

Will be called by the methods from the ICommand interface. This method is called when the Command should evaluate if it can execute.

protected virtual bool ICommandCanExecute(object? parameter)

Parameters

parameter object

The parameter being passed to the ICommand.

Returns

bool

If the command can be executed.

ICommandExecute(object?)

Will be called by the methods from the ICommand interface. This method is called when the Command should execute.

protected virtual void ICommandExecute(object? parameter)

Parameters

parameter object

The parameter being passed to the ICommand.

OnCanExecuteChanged(bool)

Will trigger a event when the CanExecute condition has changed.

protected void OnCanExecuteChanged(bool newValue)

Parameters

newValue bool

The new value of the execute.

Subscribe(IObserver<TResult>)

Subscribes to execution results from this command.

public abstract IDisposable Subscribe(IObserver<TResult> observer)

Parameters

observer IObserver<TResult>

The observer.

Returns

IDisposable

An IDisposable that, when disposed, will unsubscribe the observer.