如何为重力设置不同的值？

Question

我在Xcode中使用Sprite Kit,我想更改在重力上设置的默认值.这是我的代码:

SKSpriteNode *sprite = [SKSpriteNode spriteNodeWithImageNamed:@"sprite1.png"];
        sprite.position = CGPointMake(-100+CGRectGetMidX(self.frame), 50 + CGRectGetMidY(self.frame));
        [self addChild:sprite];
        sprite.color = [SKColor blueColor];
        sprite.colorBlendFactor = 1.0;
        sprite.xScale = 0.2;
        sprite.yScale = 0.2;
        [SKPhysicsBody bodyWithCircleOfRadius:50];
        sprite.physicsBody.dynamic = YES;
        sprite.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:sprite.size.width * 0.5];

现在我知道使用这行代码应该提供默认设置但我现在无法运行项目:

//self.physicsWorld.gravity = CGPointMake(0.0, -9.8);

救命？

Answer 1

self.physicsWorld.gravity属性由CGVector表示.所以你应该使用CGVectorMake来改变引力:

        self.physicsWorld.gravity = CGVectorMake(0.0f, -9.8f);