測試如果對象是零或不

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{ 

UITouch *touch = [touches anyObject]; 
CGPoint location = [touch locationInNode:self]; 
SKNode *node = [self nodeAtPoint:location]; 

if ([node.name isEqualToString:@"play"]){ 

    NSLog(@"play was touched"); 

    SKScene *mainGameScene = [[MainGame alloc] initWithSize:self.size]; 
    if (!mainGameScene){ 
    SKTransition *transition = [SKTransition fadeWithColor:[UIColor blackColor] duration:0.5]; 
    [self.view presentScene:mainGameScene transition:transition]; 
    } 

}

}測試如果對象是零或不

從我的理解上面的檢查的代碼，如果mainGameScene是零，如果它再通過if語句去。

這樣做有益嗎？還是隻是浪費了代碼？因爲如果多次調用此代碼的方法不會創建新對象SKScene？

來源

2014-04-12 Mutch95

如果你在'if（！mainGameScene）'之前分配/ init'mainGameScene'，那麼......看起來if塊永遠不會是真的，因此不會執行。 – staticVoidMan

如何在alloc/init之前測試一個對象？ – Mutch95

它用於檢查mainGameScene是否已初始化，因爲如果它是nil，則不能presentScene。如果你想只檢查對象初始化，然後

SKScene *mainGameScene; 
//creates new variable - place it at the beginning of the code, before @implementation and @interface 
if(mainGameScene){ 
// it is already inited (you have already tapped once), it will be called always, since it is inited at else 
//it is called when you tap the second, the third time, etcetera 
SKTransition *transition = [SKTransition fadeWithColor:[UIColor blackColor] duration:0.5]; 
[self.view presentScene:mainGameScene transition:transition]; 
}else 
{ 
//Calls only once, when you first touching the screen, and initing mainGameScene. 
//It won't be called ANYMORE, since it is inited. 
mainGameScene = [[MainGame alloc] initWithSize:self.size]; 
}

你現在的代碼是無用的，因爲它試圖做一些與對象，未初始化。
就我而言，你的mainGameScene一旦被引用就不會被重新初始化。

來源

2014-04-12 09:42:34 AlieN

所以如果這被稱爲多次，它不會每次分配一個新的'mainGameScene'？ @AlieN – Mutch95

你的init方法被調用，直到你的場景被初始化。如果它已經被初始化，它將不會被再次調用，所以它不會每次都創建一個新的mainGameScene。 – AlieN

我已經更新了代碼，也許你會理解我的意思吧？ – Mutch95

測試如果對象是零或不

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