Cocos2d-x development example: Using lambda expressions

The support for C ++ 11 standard [1] is provided after Cocos2d-x 3.0, where Lambda [2] expressions are very simple to use. We can use lambda expressions to refactor the instance in the previous section.

We can use the following code:

listener->onTouchBegan =CC_CALLBACK_2(HelloWorld::onTouchBegan, this);... ...bool HelloWorld::onTouchBegan(Touch*touch, Event* event) {    ......    returnfalse;}

 

Replace it with the following code:

listener->onTouchBegan = [](Touch*touch, Event* event){   ... ...   return false;};

The preceding statement [] (touch * touch, event * event ){...} It is a Lambda expression. Lambda expressions are anonymous functions in Javascript, while Java's anonymous internal classes are directly declared functions in expressions, rather than independent declarations.

The prompt [] in the lambda expression indicates that the lambda function is defined next. () after [] indicates the list of Lambda function parameters, and {} indicates the function body in the middle.

 

The modified code of helloworldscene. cpp after reconstruction is as follows:

Void helloworld: onenter () {layer: onenter (); log ("helloworldonenter"); Auto listener = eventlistenertouchonebyone: Create (); listener-> setswallowtouches (true ); listener-> ontouchbegan = [] (touch * touch, event * event) {① auto target = static_cast <sprite *> (Event-> getcurrenttarget ()); pointlocationinnode = target-> converttonodespace (touch-> getlocation (); Size S = target-> getcontentsize (); rect = rect (0, 0, S. width, S. height); If (rect. containspoint (locationinnode) {log ("Sprite x = % F, y = % F", locationinnode. x, locationinnode. y); log ("spritetag = % d", target-> gettag (); Target-> runaction (scaleby: Create (0.06f, 1.06f); Return true ;} return false ;}; listener-> ontouchmoved = [] (touch * touch, event * event) {② auto target = static_cast <sprite *> (Event-> getcurrenttarget ()); // move the Coordinate Position of the current button genie target-> setposition (Target-> getposition () + touch-> getdelta ());}; listener-> ontouchended = [] (touch * touch, event * event) {③ auto target = static_cast <sprite *> (Event-> getcurrenttarget ()); log ("Sprite ontouchesended .. "); pointlocationinnode = target-> converttonodespace (touch-> getlocation (); Size S = target-> getcontentsize (); rect = rect (0, 0, S. width, S. height); If (rect. containspoint (locationinnode) {log ("Sprite x = % F, y = % F", locationinnode. x, locationinnode. y); log ("Sprite tag = % d", target-> gettag (); Target-> runaction (scaleto: Create (0.06f, 1.0f ));}}; // Add the listener eventdispatcher * eventdispatcher = Director: getinstance ()-> geteventdispatcher (); eventdispatcher-> addeventlistenerwithscenegraphpriority (listener, getchildbytag (kboxtag )); eventdispatcher-> listener (listener-> clone (), getchildbytag (kboxb_tag); eventdispatcher-> listener (listener-> clone (), getchildbytag (kboxc_tag ));}

The above Code uses anonymous functions defined by lambda expressions in rows ①, ②, and ③. The specific code does not need to be explained. From the code above, the use of lambda expressions is very concise. Because callback functions do not need to be defined separately, the corresponding header file code is also concise. The main code of helloworldscene. H is as follows:

class HelloWorld : public cocos2d::Layer{public:   static cocos2d::Scene* createScene();  virtual bool init();     virtualvoid onEnter();    virtualvoid onExit();      CREATE_FUNC(HelloWorld);};

In addition to touch events, Keyboard Events, mouse events, acceleration events, and custom events, lambda expressions can also be used.

[1] C ++'s latest formal standards were published by the C ++ Standards Committee on August 12, 2011 and published on September 2011. The draft international standard (n3376) of February 28, 2012 was the most recent draft (revised) of the current standard ). This standard is the first major amendment to C ++ 98 in the 13 years after its release. -- From Baidu encyclopedia http://baike.baidu.com/view/7021472.htm

 

[2] [upper, λ], 11th of the Greek letters, and ['l? MD?].

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Cocos2d-x development example: Using lambda expressions