- .NET Core 1.0
- .NET Framework 4.5
- Mono 4.6
- Xamarin.iOS 10.0
- Xamarin.Mac 3.0
- Xamarin.Android 7.0
- Universal Windows Platform 10.0
- Unity 2018.1
Handlers should implement IHandler<TIn, TOut> interface
public interface IHandler<TIn, TOut>
{
TOut Handle(TIn input, Func<TIn, TOut> next);
}Example
/// <summary>
/// Parses work log to minutes.
/// E.g. "30m" => 30 minutes
/// </summary>
public class MinuteParser : IHandler<string, int>
{
private readonly Regex _pattern = new Regex("^(\\d+)m$");
// implement IHandler<TIn, TOut>.Handle method
public int Handle(string input, Func<string, int> next)
{
if (!_pattern.IsMatch(input))
{
// current handler cannot handle the input, so pass it to the next handler
return next.Invoke(input);
}
// parse and return number of minutes
// ...
return minutes;
}
}A composite handler then extends Handler<TIn, TOut> abstract class and add child handlers via its constructor
public class WorkLogParser : Handler<string, int>
{
public WorkLogParser(WorkLogValidator validator, IndividualUnitParser individualUnitParser)
{
AddHandler(validator);
AddHandler(individualUnitParser);
}
}A composite handler can have as many nested handlers as needed. Support for deeply nested handlers is a natural progression.
var parser = new WorkLogParser(
new WorkLogValidator(
new WorkLogMustNotBeNullOrEmptyRule(),
new ThereShouldBeNoUnitDuplicationRule(),
new UnitsMustBeInDescendingOrderRule()
),
new IndividualUnitParser(
new WeekParser(),
new DayParser(),
new HourParser(),
new MinuteParser()
)
);// work log in minutes
int workLog = parser.Handle("1w 2d 4h 30m");
Assert.Equal(3630, workLog);If the last handler in the chain cannot handle the input (and it passes the input to the next handler), the composite handler will throw an exception of type NotSupportedException by default. This can be made explicitly via chain's constructor
public class WorkLogParser : IHandler<string, int>
{
public WorkLogParser(
WorkLogValidator validator,
IndividualUnitParser individualUnitParser,
ThrowNotSupported<string, int> throwNotSupported)
{
AddHandler(validator);
AddHandler(individualUnitParser);
// explicitly tell the chain to use ThrowNotSupported as the last resort
AddHandler(throwNotSupported);
}
}or via method invocation
var workLog = parser.Handle("1w 2d 4h 30m", new ThrowNotSupported<string, int>().Handle);There are also other built-in last resort handlers
ReturnDefaultValueReturnCompletedTaskReturnCompletedTaskWithDefaultValue
For asynchronous operations, handlers should implement IAsyncHandler<TIn, TOut>
public interface IAsyncHandler<TIn, TOut> : IHandler
{
Task<TOut> HandleAsync(TIn input, Func<TIn, CancellationToken, Task<TOut>> next, CancellationToken cancellationToken);
}
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