How to put a function in a constructor and call it later in the class

Programming Questions

Pershonkey

How to put a function in a constructor and call it later in the class

in Programming Questions • 7 months ago

Hi,

I'm trying to make a few class files that could be copy/pasted into one of my sketches (Or someone else's) that would quickly let me make a button with custom/existing functions that could be easily defined in the main sketch, with only minimal other work to the main sketch, and no other modifications to the copy/pasted files besides possibly extending the class besides extending the class with the list of functions to add custom ones.

So basically, I would have a class called Functions which would be defined in the sketch as, lets say, Functions function, which the Button class would grab functions from. It would have a long series of void ...(...,...,...)s, each of which would do a certain thing, lets say, void ChangeBackground( color c), which would be called on in the Button class.

I know how to make a list of functions using a variable in the constructor that would be strained through a series of conditionals to find the right function, but I'm trying to do it where someone could add new functions by simply extending the Functions class/adding new void ...s to the existing one, instead of modifying the Button. The best way I can think to do this would be putting a variable in the Button class that would be set to a function, which would then be used to call on part of the Functions class which the button of pressed.

Define the Functions class in the sketch (Functions function = new Functions()) --> Constructor (For example: test = new Button(...,...,...,function.ChangeBackground( color(...,...,...)))) --> Have a variable in the class be set to the function --> Call on the function using the variable in a part of the class

I'm not sure if this is possible, and what I've done so far hasn't resulted in anything more than constructor errors, function errors, and the occasional NPE. If anyone has any ideas to help, they would be much appreciated.

Main sketch:

Button test;
Functions function;
void setup() {
imageMode(CENTER);
size(500,500);
test = new Button(width/2,height/2,50,50,loadImage("Musketeer.png"),loadImage("Galleon.png"),"Hello!",function.ChangeBackground(color(255,0,0)));
function = new Functions();
}
void draw() {
test.Display();
}
void mousePressed() {
test.mousePressed();
}

Button class:

class Button {
PVector location; //Location of the button
int xSize,ySize; //Size ofthe button
PImage on,off; //Images for mosue overlap
String type; //Text to be displayed in the button
boolean mouseOver;
void callFuntion;
Button(float x, float y, int xs, int ys, PImage ion, PImage ioff, String t, void a) {
location = new PVector(x,y);
xSize = xs;
ySize = ys;
on = ion;
off = ioff;
type = t;
callFuntion = a;
}
boolean mouseOver(float x, float y, float sizeX, float sizeY) {
x-=sizeX/2;
y-=sizeY/2;
if(mouseX>x&&mouseX<x+sizeX&&mouseY>y&&mouseY<y+sizeY) {
return true;
} else {
return false;
}
}
void Display() {
if(mouseOver(location.x,location.y,xSize,ySize)) {
image(off,location.x,location.y,xSize,ySize);
}
else if(!mouseOver(location.x,location.y,xSize,ySize)) {
image(on,location.x,location.y,xSize,ySize);
}
text(type,location.x-(xSize/2),location.y);
}
void mousePressed() {
if(mouseOver(location.x,location.y,xSize,ySize)) {
}
}
}

Functions class:

class Functions {
Functions() {
}
void ChangeBackground(color c) {
background(c);
}
void ChangeFill(color c) {
fill(c);
}
void ChangeTint(color c) {
tint(c);
}
void ChangeStroke(color c) {
stroke(c);
}
void ChangeFont(PFont s) {
textFont(s);
}
void ChangeFontSize(int a) {
textSize(a);
}
void DrawShape(float x, float y) {
point(x,y);
}
void DrawShape(String s, float x, float y, float w, float h) {
if(s=="RECT") {
rect(x,y,w,h);
}
else if(s=="ELLIPSE") {
ellipse(x,y,w,h);
}
else if(s=="LINE") {
line(x,y,w,h);
}
}
void DrawShape(float x1, float y1, float x2, float y2, float x3, float y3) {
triangle(x1,y1,x2,y2,x3,y3);
}
void DrawText(String s, float x, float y) {
text(s,x,y);
}
}

Replies(5)

quarks

Re: How to put a function in a constructor and call it later in the class

7 months ago

The best way I can think to do this would be putting a variable in the Button class that would be set to a function, which would then be used to call on part of the Functions class which the button of pressed.

Yes this is probably the best way to do it. The variable in the Button class would be of type Method and would be 'invoked' when the button is pressed. It would involve learning to program using the Java reflection classes and that is going to take some effort to learn on your part.

If you want a ready built solution try G4P with the GUI builder tool, it allows you to design a GUI with buttons and then name the method (funtion) to call when the button is clicked.

PhiLho

Re: How to put a function in a constructor and call it later in the class

7 months ago

I admit I only skimmed through your description, a bit confusing.
But I feel you missed the main interest of making a class: it is a data structure that carries its own functions (generally called methods in the Java world), no need to put them in a separate class.
What's more with classes is that you can extend them: you can make a sub-class of your Button class, adding its own functions, or even redefining the existing ones. A method redefining the method of the super-class can also call this one, to keep the original behavior and to modify it.
It is quite flexible and powerful...

To address specifically your title: basically, in Java, you cannot put a function in a variable.
A way to emulate this is to make a class with only one function, then store an instance of this class in a variable. It is often done with interfaces and anonymous classes implementing them.

Pershonkey

Re: How to put a function in a constructor and call it later in the class

6 months ago

Thanks guys! I'm sorry the OP was very cluttered, I should have realized that...

The reason I wanted to store a list of functions methods in another class would simply be to keep the Button class less cluttered, and to just allow someone to extend the Functions class and add more methods instead of extending the Button class. It would be a pain to have to make an extension of the button class for each simple generic method I want available, Eg:

Class Button

Class ButtonChangeBackground extends Button

Class ButtonChangeFill extends Button

Class ButtonChangeStroke extends Button

Class ButtonChangeStrokeWeight extends Button...

And so forth.

I know its a little silly to make methods for each of these things, but I have my reasons, trust me.

PhiLho

Re: How to put a function in a constructor and call it later in the class

6 months ago

As usual, we get a description of a possible way to solve a problem (possibly a wrong way...) instead of a description of the problem itself, that might be solved by another way...

Why would you need a specialized sub-class per function?
The usual use case is to have a base class, which can store all the settings it need, and which provides accessors (at least setters) to read and write these settings.
If you need a specialized class to do something very special with some setting(s), you can do it on the fly, for one button or a series.

el_dippo

Re: How to put a function in a constructor and call it later in the class

6 months ago

I like the idea. I had/have the same question like you. The problem is very complicated and hard to describe. The solution lies (i think) in BeanShell, where you run your program and create a class within your program that act's like a function.
The problem with BeanShell, is that it's slow and light weight. How to make it fast?

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