After some years of coding, I found myself watching code with callbacks, and although I practiced several times and watched several videos, I couldn’t understand it well. Today I’ll write this blog in the hope of being useful for others
First, we need to see a common example
Piece of cake: First
GetS3List is called, and later
ActivatePanel. Common case.
Now, a callback, as I understood (If it’s not correct, please let me know), executes a whole line of code before continuing the program execution
If you see above, the code execution is:
As you can see, we are executing 1 step, and after it’s done, we continue with the second step.
Now, let’s say I want the whole code (both steps,
ActivatePanel) to be executed before continuing the program execution flow.
Normally, a method allow parameters as int, string, etc. and later it executes some code
And for instance, this won’t be allowed
AddValue declaration only allows primitive type parameters as said before (int, string)
AddValue, Increase value is not declaring its type, and below, it’s declaring itself as a method, that is not allowed in this case
For these cases, the Delegates are the solution
Delegates is a special type of variables that allow you to assign a method to them. For example
It assigns the
MethodA to delegate variable
Or use a lambda expression to execute the code immediately
Example of implementing a Delegate
Now, we will use an Action
What is an Action? It’s a special type Delegate
An Action can get a method as its value and execute it, without declaring a Delegate and later assigning a new variable
Another example with less code but harder to read
Let’s say that in this example shown before, it executes one line and later the other one
Let’s say we do need to execute the WHOLE code snippet before continuing the program execution. Here is where the Action, well, takes Action…
First, we need to modify the
GetS3List method signature
The only way to verify if Action is not null is when the
GetS3List method is called
The method execution (method call):
- Starts in the orange line
- Gets the caseNumberInput.text value
- Executes the whole code contained in the Action (green area, strange but it’s the anonymous way)
- Finishes after the second orange line
The objective is to execute the whole line of code and later continue the program execution, but maybe we want to execute the whole code but without stopping the program execution. That is why this Action execution (also called as a callback) is executed as a Asynchronous operation.
It means that the Action code will be executed in the background while the program continues its execution flow
That’s all !