Category Archives: Uncategorized

Ok, the headline sounds a little bit funny, because first of all, dynamic objects have no properties. Also you can not use reflection on a dynamic type, because it’s dynamic. What I actually want to do, is to access values of a dynamic object by its name – but I don’t know the name of the property on compile time, but during execution.

I want to do something like that:

dynamic obj = GetDynamicObject();
string myPropertyValue = DynamicExtension.GetValue(obj, "MyProperty");
DynamicExtension.SetValue(obj, "MyProperty", "some cool value");

So how can we do this? Reflection is not possible, and not all dynamic types impement IDictionary like ExpandoObject.

But how can we achieve this? By looking at the disassembled code, of a dynamic class, and the way it is accessed, we can find out, how we can access it ourself…

dynamic dynObj = new TestClass
{
  TestProperty = "Hello World",
  TestInt = 20
};
var val = dynObj.TestProperty;
dynObj.TestProperty = "Hello C#";

Because I don’t want to flood this post, I just copied the essentials from the IL. Basically there are 2 parts:
1. create a Binder
2. create a CallSite to execute the getter/setter.

// the getter
            var binder = Binder.GetMember(
                CSharpBinderFlags.None,
                "TestProperty",
                typeof(object),
                new CSharpArgumentInfo[] { 

 CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.NamedArgument, null)
                });

            var getter = CallSite<Func<CallSite,object,object>>.Create(binder);
            var val = getter.Target(getter,  dynObj);

// the setter
var setterBinder = Binder.SetMember(
    CSharpBinderFlags.None,
    "TestProperty",
    typeof(object),
    new CSharpArgumentInfo[] {
        CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null),
        CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.UseCompileTimeType, null) });
// the IL actually uses string as value type, but we use object here, to be more flexible
var setter = CallSite<Func<CallSite,object,object,object>>.Create(setterBinder);
setter.Target(setter, dynObj, "Hello C#");

So now just wrap it up to our two functions:

    public static class DynamicHelper
    {
        public static object GetValue(object obj, string name)
        {
            var binder = Binder.GetMember(
                        CSharpBinderFlags.None,
                        name,
                        typeof(object),
                        new CSharpArgumentInfo[] {
                            CSharpArgumentInfo.Create(
                                CSharpArgumentInfoFlags.NamedArgument,
                                null)
                        });

            var getter = CallSite<Func<CallSite,object,object>>.Create(binder);
            return getter.Target(getter, obj);
        }

        public static void SetValue(object obj, string name, object value)
        {
            var setterBinder = Binder.SetMember(
                CSharpBinderFlags.None,
                name,
                typeof(object),
                new CSharpArgumentInfo[] {
                  CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null),
                  CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.UseCompileTimeType, null) });
            // the IL actually uses string as value type, but we use object here, to be more dynamic
            var setter = CallSite<Func<CallSite,object,object,object>>.Create(setterBinder);
            setter.Target(setter, obj, value);
        }
    }

Arduino Object-oriented

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It has been more than a decade, that I switched over to programming in C# and even longer I am developing object-oriented code. But when it comes to Arduino, I can not count on C#. (Actually, there is an Arduino-like microcontroller, which can be programmed with C#. It is called Netduino) But we can still produce object-oriented code with Arduino.

Let’s first have a look at a simple Blink-App (from the Arduino tutorial).

// the setup function runs once when you press reset or power the board
void setup() {
// initialize digital pin LED_BUILTIN as an output.
pinMode(LED_BUILTIN, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
delay(1000); // wait for a second
digitalWrite(LED_BUILTIN, LOW); // turn the LED off by making the voltage LOW
delay(1000); // wait for a second
}

As you can see, there are two standard functions, that get called, when the code is deployed on the device. setup() when the device starts, and loop(), which is something like a while(true)-loop after the setup finished. The code does that, what it is meant to do, make a LED blink every second. But let’s assume we have a button, that shall turn the blinking on and off. My OOP-brain always keeps saying:

“There should be a LED-object and a Button-object”

I can imagine, that there are other solutions, but that was the first thing, that comes in mind when I think about it. So let’s draw something…

When we now come to the point to include those objects in the Standard setup-loop-pattern, we also need a loop and setup-function in each of the classes. These could be called from the main functions.

Here comes the code:

enum SwitchState
{
On,
Off
};
//---------- Light
class Light
{
SwitchState _currentState = Off;
byte _pin;

public:
Light(byte pin)
{
_pin = pin;
}
SwitchState GetCurrentState()
{
return _currentState;
}
// turns on the light
void TurnOn()
{
_currentState = On;
}

// turns off the light
void TurnOff()
{
_currentState = Off;
}

void Setup()
{
pinMode(_pin, OUTPUT);
}

void Loop()
{
if (_currentState == On)
{
digitalWrite(_pin, HIGH);
}
else
{
digitalWrite(_pin, LOW);
}
}
};
//---------- Button
class Button
{
SwitchState _currentState = Off;
byte _pin;

void OnSwitchChanged()
{
SwitchChangedEvent();
}

public:
void(* SwitchChangedEvent)();

Button(byte pin)
{
_pin = pin;
}

SwitchState GetCurrentState()
{
return _currentState;
}

void Setup()
{
pinMode(_pin, INPUT);
}

void Loop()
{
byte val = digitalRead(_pin);
if (val == HIGH && _currentState == Off)
{
_currentState = On;
OnSwitchChanged();
}
else if (val == LOW && _currentState == On)
{
_currentState = Off;
OnSwitchChanged();
}
}
};

//-------------------------- MAIN
Light led1(1);
Button button1(2);

void InvertLight()
{
if (led1.GetCurrentState()==Off)
{
led1.TurnOn();
}
else
{
led1.TurnOff();
}
}

void setup() {
led1.Setup();
button1.Setup();
button1.SwitchChangedEvent = InvertLight;
}

void loop() {
led1.Loop();
button1.Loop();
}

From this starting point, you can do a lot of fancy stuff. First of all, you could implement a base class, to actually wrap up those functions, that tend to produce code doubles. Also you may not want to trigger (and write) the digital pins on every loop. You can simply introduce something like a timestamp, skipping the loop for an amount of time. Everything can be made in a base class, so there will be no need to implement it every time again.

Tom's Tech Blog

www.kison.info

Category Archives: Uncategorized

CSC : error CS1703: Multiple assemblies with equivalent identity have been imported (iOS)

read and write properties on dynamic objects in .NET/C#

Arduino Object-oriented