How to Listen Keys in JScript.Net

Question

What I wish is to catch the keypress using JScript .NET, and compile the code using that jsc.exe. So, is there any equivalent of "addEventListener("keyDown", keyCheck)" from FLASH actionscript. Or GetAsyncKeyState() from C++. And what library do I have to use? Please be kind enough to share a small, simple example.

Answer 1

Here's a simple solution if you're writing a console app.

import System;

Console.Write("Press the M key... ");

var key:ConsoleKeyInfo;

while (1) {
    while (!Console.KeyAvailable) {
        System.Threading.Thread.Sleep(1);
    }
    key = Console.ReadKey(1);
    if (key.Key == ConsoleKey.M) break;
}

Console.Write("Accepted.");

Read more about ConsoleKeyInfo.

---

If you need GetAsyncKeyState(), it is possible to access the method in JScript.NET. A couple days ago I came across a JScript.NET function that exposes Win32 API methods via P/Invoke. Here it is, slightly modified for simpler syntax (allowing pass-through of arguments from API function definitions).

import System;
import System.Reflection;
import System.Reflection.Emit;

// Invoke a Win32 P/Invoke call.
// credit: http://cx20.main.jp/blog/hello/2013/03/07/hello-win32-api-jscript-net-world/
function InvokeWin32(dllName:String, returnType:Type, methodName:String, params:Object[]) {

    var paramTypes:Type[] = new Type[params.length];
    for (var i:int in params) {
        paramTypes[i] = params[i].GetType();
    }

    // Begin to build the dynamic assembly
    var domain = AppDomain.CurrentDomain;
    var name = new System.Reflection.AssemblyName('PInvokeAssembly');
    var assembly = domain.DefineDynamicAssembly(name, AssemblyBuilderAccess.Run);
    var module = assembly.DefineDynamicModule('PInvokeModule');
    var type = module.DefineType('PInvokeType',TypeAttributes.Public
        + TypeAttributes.BeforeFieldInit);

    // Define the actual P/Invoke method
    var method = type.DefineMethod(methodName, MethodAttributes.Public
        + MethodAttributes.HideBySig + MethodAttributes.Static +
        MethodAttributes.PinvokeImpl, returnType, paramTypes);

    // Apply the P/Invoke constructor
    var ctor = System.Runtime.InteropServices.DllImportAttribute.GetConstructor(
        [System.String]
    );
    var attr = new System.Reflection.Emit.CustomAttributeBuilder(ctor, [dllName]);
    method.SetCustomAttribute(attr);

    // Create the temporary type, and invoke the method.
    var realType = type.CreateType();
    return realType.InvokeMember(methodName, BindingFlags.Public + BindingFlags.Static
        + BindingFlags.InvokeMethod, null, null, params);
}

With this function, you can expose Win32 DLL methods with the following syntax. (See? Told you it was simpler.)

// ShowWindowAsync(hWnd:IntPtr, nCmdShow:int);
function ShowWindowAsync(... args:Object[]):boolean {
   return InvokeWin32("user32.dll", System.Boolean, "ShowWindowAsync", args);
}

// GetWindowLong(hWnd:IntPtr, nIndex:int);
function GetWindowLong(... args:Object[]):int {
    return InvokeWin32("user32.dll", System.Int32, "GetWindowLong", args);
}

// FindWindowEx(parentHandle:IntPtr, childAfter:IntPtr,
//      lclassName:IntPtr, windowTitle:String);
function FindWindowEx(... args:Object[]):IntPtr {
    return InvokeWin32("user32.dll", System.IntPtr, "FindWindowEx", args);
}

And I've never used GetAsyncKeyState(); but since it's a user32.dll method, I'm guessing it'll work the same way. (Edit: It does.)

// GetAsyncKeyState(vKey:int);
function GetAsyncKeyState(... args:Object[]):short {
    return InvokeWin32("user32.dll", System.Int16, "GetAsyncKeyState", args);
}

Then for a trivial example:

import System;               // for Console methods
import System.Windows.Forms; // for Keys object constants

Console.Write("Press the M key... ");

// while the M key is not being pressed, sleep
while (!GetAsyncKeyState(Keys.M)) {
    System.Threading.Thread.Sleep(1);
}

// flush input buffer
while (Console.KeyAvailable) Console.ReadKey(1);

Console.WriteLine("Accepted.");