Add helper package to easier use of Cocoa API with Go (#163)

helper/helper.go

@@ -0,0 +1,46 @@
+package helper
+
+import "runtime"
+import "reflect"
+import "strings"
+import "fmt"
+import "github.com/progrium/macdriver/objc"
+import "github.com/progrium/macdriver/cocoa"
+
+
+// Adds the ActionHelper class to the objective-c system
+func init() {
+	newClass := objc.NewClass("ActionHelper", "NSObject")
+	objc.RegisterClass(newClass)
+}
+
+
+// Creates a unique method name using a control and a Go function
+func createActionName(control interface{}, callback func(sender interface{})) string {
+	actionName := runtime.FuncForPC(reflect.ValueOf(callback).Pointer()).Name()
+	actionName = fmt.Sprintf("%s%s", actionName, control)
+
+	// remove any characters that should not be in a method's name
+	actionName = strings.ReplaceAll(actionName, " ", "") // remove space
+	actionName = strings.ReplaceAll(actionName, ":", "") // remove middle colon
+	actionName = strings.ReplaceAll(actionName, "<", "") // remove <
+	actionName = strings.ReplaceAll(actionName, ">", "") // remove >
+	actionName = actionName + ":"						 // add colon at end
+	return actionName
+}
+
+
+// Sets a control's action and target for use with a Go function
+// Input 1: control - NSControl subclass
+// Input 2: callback - a Go function that has one argument of interface{}
+func SetAction(control cocoa.NSControlRef, callback func(sender interface{})) {
+	actionClass := objc.Get("ActionHelper")
+	actionName := createActionName(control, callback)
+	actionClass.AddMethod(actionName, func(sender objc.Object){
+		callback(control)
+	})
+	theControl := cocoa.NSControl_FromRef(control)
+	actionObj := actionClass.Alloc()
+	theControl.SetTarget(actionObj)
+	theControl.SetAction(objc.Sel(actionName))
+}