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This article will explain in detail how the key callback of the callback function in cocos2d-x is, and the content of the article is of high quality, so the editor will share it for you as a reference. I hope you will have some understanding of the relevant knowledge after reading this article.

Callback function is the key to interface interaction and access to a variety of third-party SDK, because the callback function C++ code can not be automatically generated, everything needs to be handwritten.

The good thing is that the Cocos2d-x engine provides a complete wrapper mechanism for callback functions. All we need to do is understand this mechanism and use it. Learn from the engine's own code examples, you can quickly and accurately use this mechanism.

First, we created a new cross-platform JS project in Cocos2d-x 3.0 beta using his own project creation tool. By convention, this is a helloworld project. While XCode is running, we can see the callback button in the lower right corner. Let's see how he did it. To do it in two processes:

1. Bind callback function process

First, we need to find the binding code of the callback function JS. In myApp.js, in the init function, you can see the following code:

12 3 4 5 6 7 8 9 10 11 12//

Add a "close" icon to exit the progress. It's an autorelease objectvar closeItem

= cc.MenuItemImage.create ("res/CloseNormal.png", "res/CloseSelected.png", function ()

{cc.log ("close

Button was clicked. ");}, this); closeItem.setAnchorPoint (cc.p (0.5)

0.5)); var menu

= cc.Menu.create (closeItem); menu.setPosition (cc.p (0)

0)); this.addChild (menu

1); closeItem.setPosition (cc.p (size.width

-20, 20)

The third argument to the cc.MenuItemImage.create function is bound to the anonymous callback function. The fourth parameter is the this when the callback function is called (if you don't understand the this mechanism of JS, please read some JS materials first). These are JS code with obvious intention and function, needless to say.

Then, we look at the underlying corresponding execution of the C++ code. In the cocos2d_specifics.cpp file, find the js_cocos2dx_CCMenuItemImage_create function.

12 34 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46//

"create" in JS//

Cc.MenuItemImage.create (normalImage, selectedImage, [disabledImage], callback_fn, [this] JSBool

Js_cocos2dx_CCMenuItemImage_create (JSContext * cx, uint32_t argc, jsval * vp) {if (argc)

> = 2 & & argc = 3) {thirdArgIsString

= argv [2] .isString (); if (thirdArgIsString)

{arg2.set (argv [2])

Cx); last

= 3;}} cocos2d::MenuItemImage*

Ret = cocos2d::MenuItemImage::create (arg0.get (), arg1.get (), std::string (arg2.get (); if (argc)

> = 3) {if (! thirdArgIsString)

{/ / cc.MenuItemImage.create (

NormalImage, selectedImage, callback_fn, [this]) jsCallback

= argv [last++]; if (argc

= = 4) {jsThis

= argv [last];}} else {/ / cc.MenuItemImage.create (

NormalImage, selectedImage, disabledImage, callback_fn, [this]) if (argc

> = 4) {jsCallback

= argv [last++]; if (argc

= = 5) {jsThis

= argv [last];} JSObject

* obj = bind_menu_item (cx, ret, jsCallback, jsThis); JS_SET_RVAL (cx

Vp, OBJECT_TO_JSVAL (obj); return JS_TRUE;} JS_ReportError (cx, "Invalid)

Number of arguments. Expecting: 2

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