Delegates #1 - Introduction « Aliasing Games DevBlog

Delegates – introduction

Have you ever used delegates? If not, the time has come to learn what delegates are. In this quick post we will show you delegates’ basics. As the title says, it will be short introduction which presents only fundamental usage of delegates.

Let’s start with Microsoft’s MSDN C# documentation. There is a short delegate’s definition:

A delegate is a type that safely encapsulates a method, similar to a function pointer in C and C++. Unlike C function pointers, delegates are object-oriented, type safe, and secure. The type of a delegate is defined by the name of the delegate.

The most intuitive way is to treat delegates as pointers to lists of functions. It’s not a mistake – delegate can “have” more than one function! To create a simple delegate just declare:

private delegate float SimpleDelegate(int par0, string par1, bool par2);
private SimpleDelegate simpleDelegate;

1 2	private delegate float SimpleDelegate(int par0, string par1, bool par2); private SimpleDelegate simpleDelegate;

Short explanation: simpleDelegate can point at any function (or functions) which has three parameters (integer, string and boolean) and returns float as result. It can be also passed as argument into another function. To show delegate in action let’s look at this simple code snippet:

using UnityEngine;
using System.Collections;

public class DelegatesTest : MonoBehaviour {

	private delegate void MultiplyDelegate (float val);

	private MultiplyDelegate multiplyDelegate;

	void Awake() {
		// assign first method to delegate
		multiplyDelegate = DoubleVal;
		multiplyDelegate (5f); // execute

		// assing second method to delegate
		multiplyDelegate = TripleVal;
		multiplyDelegate (10f);

		// remove TripleVal method from delegate
		multiplyDelegate -= TripleVal;

		// add both methods
		multiplyDelegate += DoubleVal;
		multiplyDelegate += TripleVal;
		PassDelegateAsArgument (multiplyDelegate);
	}

	private void DoubleVal (float val) {
		Debug.Log (string.Format ("2 * {0} = {1}", val, 2f * val));
	}

	private void TripleVal (float val) {
		Debug.Log (string.Format ("3 * {0} = {1}", val, 3f * val));
	}

	private void PassDelegateAsArgument(MultiplyDelegate del) {
		del (20f);
	}
}

using UnityEngine;

using System.Collections;

public class DelegatesTest : MonoBehaviour {

private delegate void MultiplyDelegate (float val);

private MultiplyDelegate multiplyDelegate;

void Awake() {

// assign first method to delegate

multiplyDelegate = DoubleVal;

multiplyDelegate (5f); // execute

// assing second method to delegate

multiplyDelegate = TripleVal;

multiplyDelegate (10f);

// remove TripleVal method from delegate

multiplyDelegate -= TripleVal;

// add both methods

multiplyDelegate += DoubleVal;

multiplyDelegate += TripleVal;

PassDelegateAsArgument (multiplyDelegate);

}

private void DoubleVal (float val) {

Debug.Log (string.Format ("2 * {0} = {1}", val, 2f * val));

}

private void TripleVal (float val) {

Debug.Log (string.Format ("3 * {0} = {1}", val, 3f * val));

}

private void PassDelegateAsArgument(MultiplyDelegate del) {

del (20f);

}

To use this script in Unity just create new project, insert empty object into scene and attach script to it. Then press Play and check Console for results. What do you see? If everything is set up correctly you have to see four new lines with multiplications. That’s the power of delegates that you can fire many methods at once and also use them as well as other functions’ arguments.

That’s all for now. In next posts we will show you more practical use of delegates in Unity projects to create clean and robust pieces of code!

Cheers,
Aliasing Games Team!

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Delegates #1 – Introduction

Delegates – introduction

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