arrays - 将一个数组选项取出一个周期

Question

好吧，我有这样的代码，其中将生成位置放入数组中，然后使用以下代码随机选择其中一个位置:

let randx = spawnLocations[Int(arc4random_uniform(UInt32(spawnLocations.count)))]
            obstacle.position = CGPoint(x: randx, y: 0)

对象生成代码:

var spawnLocations:[CGFloat] = [] 

func getObjectSpawnLocation() {

//Create 5 possible spawn locations
let numberOfNodes = 5

    // Spacing between nodes will change if: 1) number of nodes is changed, 2) screen width is changed, 3) node's size is changed.
    for i in 0...numberOfNodes - 1 {

        // spacing used to space out the nodes according to frame (which changes with screen width)
        var xPosition = (frame.maxX /*- thePlayer.size.width*/) / CGFloat((numberOfNodes - 1)) * CGFloat(i)

        //add a half of a player's width because node's anchor point is (0.5, 0.5) by default
        xPosition += thePlayer.size.width/2

        //I have no idea what this does but it works.
        xPosition -= frame.maxX/1.6
        spawnLocations.append( xPosition )

    }
  ()
}

但我有一个问题，因为有时游戏会生成如下图所示的对象，并且它不会让我的玩家在不死亡的情况下进一步前进，所以我的问题是:

我有办法阻止它这样做吗？

也许可以暂时从数组中取出一个生成位置？

我还应该注意到，每个对象(头骨)都是一个接一个地生成的，而不是同时生成，并且头骨可以在 5 个水平位置中的任何一个位置生成。

Answer 1

玩家只能被困在头骨和屏幕边缘之间。您应该跟踪当前是否正在“楔入”玩家，例如:

//Keep instance variables to track your current state
BOOL lineFromEdge; //YES if you're currently drawing a "line" of skulls from an edge
BOOL leftEdge; //YES if the line originates from the left edge, NO if from the right
int previousIndex;

然后按如下方式确定该值:

- (int) randomIndex {

    int randIndex = Int(arc4random_uniform(UInt32(spawnLocations.count)));

    // This expression tells you if your current index is at an edge
    if (randIndex == 0 || randIndex == (spawnLocations.count - 1)) {
        lineFromEdge = YES;
        leftEdge = randIndex == 0;
    }

    //Check if you left a gap
    BOOL didLeaveGap = abs(randIndex - previousIndex) > 1
    if (didLeaveGap) lineFromEdge = NO;

    if ((lineFromEdge && leftEdge && randomIndex == spawnLocations.count) ||
        (lineFromEdge && !leftEdge && randomIndex == 0)) {

        //You have drawn a line from one edge to the other without leaving a gap;
        //Calculate another index and perform the same checks again
        return [self randomIndex];

    }

    //Your index is valid
    previousIndex = randIndex;
    return randIndex;
}

Note: Your algorithm must return 0 or spawnLocations.count as very first index for this to work. Else your skulls may start at the center and still wedge the player in without you realizing it.