更新方法是可以做到的:

Update method is where you can do it alright:

- (void)update:(NSTimeInterval)currentTime {
    //remove any nodes named "yourNode" that make it off screen
    [self enumerateChildNodesWithName:@"yourNode" usingBlock:^(SKNode *node, BOOL *stop) {

        if (node.position.x < 0){
            [node removeFromParent];
        }
    }];
}

请注意，删除节点并不能保证释放内存！！

Though note that removing nodes doesn't guarantee freeing up memory!!