Android启发式寻路

实现的效果图

Screenshot_20181213-143828.jpeg

思路分析

根据启发算法理论 f(n) = g(n)+h(n); 其中，g(n)表示实际代价（即已经走过的路程），h(n)代表预估代价，由于使用的网格构造，所以使用曼哈顿距离公式，表示h(n)。

代码实现

数据结构（采用单向链表）

  public class Node implements Comparable {
Coord coord;
Node parent;
int g; // G：是个准确的值，是起点到当前结点的代价
int h; // H：是个估值，当前结点到目的结点的估计代价

public Node(int x, int y) {
    this.coord = new Coord(x,y);
}

public Node(int x, int y, Node parent, int h, int g) {
    this.coord = new Coord(x,y);
    this.parent = parent;
    this.h = h;
    this.g = g;
}

public Node getParent() {
    return parent;
}

public void setParent(Node parent) {
    this.parent = parent;
}

public int getH() {
    return h;
}

public void setH(int h) {
    this.h = h;
}

public int getG() {
    return g;
}

public void setG(int g) {
    this.g = g;
}

@Override
public int compareTo(@NonNull Node o) {
    return g+h - (o.g+o.h);
}

@Override
public boolean equals(Object obj) {
    Node node = (Node) obj;
    return coord.x == node.coord.x && coord.y == node.coord.y;
}

}

说明：

由于寻路需要通过一个点找附近最近的点，最终形成一条多段的线段，在数据结构中与单向链表吻合，故选择单向链表存储。compareTo方法是按f(n)大小排序。

核心代码思路

1.将起点加入开放列表
2.从开放列表中移除掉其中f(n)最小的一个Node，并将该节点加入到关闭列表
3.从该节点向周围扩展，如果符合条件，则加入到开放列表
4.重复23步骤直至终点与2步骤的节点重合

代码：

 public class Astart {
   private int[][] map;
   private int width;
   private int height;
    private Node start;
   private Node end;
   private PriorityQueue openList = new PriorityQueue<>();
   private List closeList = new ArrayList<>();

   public Astart(@NonNull int[][] map, @NonNull Node start, @NonNull Node end)     
    {
    this.map = map;
    this.start = start;
    this.end = end;
    height = map.length;
    width = map[0].length;
  }

public Stack start() {
    //将起点放入开放列表
    openList.add(start);
    while (!openList.isEmpty()) {
        //将曼哈顿距离最近的点取出
        Node node = openList.poll();
        //将节点放入关闭列表中
        System.out.println(node.coord);
        closeList.add(node);
        //如果取出来的最近的点为终点，结束循环
        if (end.equals(node)) {
            end = node;
            break;
        }
        //将扩展的节点加入开放列表(朝八個方向)
        addNeighborNode(node);

    }
    //把关闭列表选中
    Node node = end;
    //将数据依次放入栈实现链表倒序
    Stack pathStack = new Stack<>();
    while (node != null) {
        pathStack.push(node);
        node = node.parent;
    }
    return pathStack;
}

/**
 * 向八个方向扩展添加节点
 *
 * @param node
 */
private void addNeighborNode(Node node) {
    Node left = new Node(node.coord.x - 1, node.coord.y);
    left.setParent(node);
    left.setG(generateG(left));
    left.setH(generateH(left));
    Node right = new Node(node.coord.x + 1, node.coord.y);
    right.setParent(node);
    right.setG(generateG(right));
    right.setH(generateH(right));
    Node top = new Node(node.coord.x, node.coord.y - 1);
    top.setParent(node);
    top.setG(generateG(top));
    top.setH(generateH(top));
    Node bottom = new Node(node.coord.x, node.coord.y + 1);
    bottom.setParent(node);
    bottom.setG(generateG(bottom));
    bottom.setH(generateH(bottom));
    Node leftTop = new Node(node.coord.x - 1, node.coord.y - 1);
    leftTop.setParent(node);
    leftTop.setG(generateG(leftTop));
    leftTop.setH(generateH(leftTop));
    Node leftBottom = new Node(node.coord.x - 1, node.coord.y +1);
    leftBottom.setParent(node);
    leftBottom.setG(generateG(leftBottom));
    leftBottom.setH(generateH(leftBottom));
    Node rightTop = new Node(node.coord.x + 1, node.coord.y - 1);
    rightTop.setParent(node);
    rightTop.setG(generateG(rightTop));
    rightTop.setH(generateH(rightTop));
    Node rightBottom = new Node(node.coord.x + 1, node.coord.y + 1);
    rightBottom.setParent(node);
    rightBottom.setG(generateG(rightBottom));
    rightBottom.setH(generateH(rightBottom));
    addNeighborSingleNode(left);
    addNeighborSingleNode(right);
    addNeighborSingleNode(top);
    addNeighborSingleNode(bottom);
    //        addNeighborSingleNode(leftTop);
    //        addNeighborSingleNode(leftBottom);
    //        addNeighborSingleNode(rightTop);
    //        addNeighborSingleNode(rightBottom);
}

/**
 * 单独添加一个相邻节点
 *
 * @param node
 */
private void addNeighborSingleNode(Node node) {
    if (canAdd(node)) {
        openList.add(node);
    }
}


private int generateG(Node node) {
    if (node.parent != null) {
        Node parent = node.parent;
        int c = (Math.abs(start.coord.x - node.coord.x) + Math.abs(start.coord.y - node.coord.y))*100;
        return parent.h + c;
    }
    return 0;
}

private int generateH(Node node) {
    return Math.abs(end.coord.x - node.coord.x) + Math.abs(end.coord.y - node.coord.y)*100;
}

/**
 * 能否添加进开放列表
 *
 * @param node
 * @return
 */
private boolean canAdd(Node node) {
    if (node == null || node.coord == null) {
        return false;
    }
    int x = node.coord.x;
    int y = node.coord.y;
    //如果超过边界 false
    if (x < 0 || x > width - 1) {
        return false;
    }
    if (y < 0 || y > height - 1) {
        return false;
    }
    //如果节点在地图上位墙壁 false
    int mapPoint = map[y][x];
    if ( mapPoint == MapUtils.WALL) {
        return false;
    }
    //如果节点在开放列表或者关闭列表中 false
    if (openList.contains(node)) {
        return false;
    }
    if (closeList.contains(node)) {
        return false;
    }
    return true;
}

界面代码

public class MainActivity extends AppCompatActivity {

private Node start;
private Node end;
private ShowMapView showMapView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    showMapView = findViewById(R.id.show);
    showMapView.init(MapUtils.map, new ShowMapView.OnTouchListener() {
        @Override
        public void onTouchPoint(int type, int row, int col) {
            if (type == 1) {
                start = new Node(col, row);
            } else {
                end = new Node(col, row);
            }
        }
    });
}

private void findWayAndDraw() {
    if (start != null && end != null) {
        Stack pathList = new Astart(MapUtils.map, start, end).start();
        Path path = new Path();
        path.moveTo(start.coord.x * 80 + 40, start.coord.y * 80 + 40);
        while (!pathList.empty()) {
            Node node = pathList.pop();
            path.lineTo(node.coord.x * 80 + 40, node.coord.y * 80 + 40);
        }
        showMapView.setPath(path);
    }


}

public void cal(View view) {
    findWayAndDraw();
}

public void reset(View view) {
    showMapView.reset();
}
}

布局文件

说明

ShowMapView为地图控件

   public class ShowMapView extends View {
   private int touchFlag;
   private int[][] map;
   private Path path;
     private OnTouchListener listener;

  public ShowMapView(Context context) {
      super(context);
  }

public ShowMapView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
}

public ShowMapView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
}


public void init(int[][] map, OnTouchListener listener) {
    this.map = map;
    this.listener = listener;
    invalidate();
}

public void setPath(Path path) {
    this.path = path;
    invalidate();
}

public void reset() {
    touchFlag = 0;
    for (int i = 0; i < map.length; i++) {
        for (int j = 0; j < map[i].length; j++) {
            if (map[i][j] == 2) {
                map[i][j] = 0;
            }
        }
    }
    path.reset();
    invalidate();
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    if (touchFlag >= 2) {
        return super.onTouchEvent(event);
    }
    float x = event.getX();
    float y = event.getY();
    //每格地图大小为80*80,注意:数组和屏幕坐标X和Y相反
    int row = (int) y / 80;
    int col = (int) x / 80;
    if (map[row][col] == 0) {
        touchFlag++;
        if (listener != null) {
            listener.onTouchPoint(touchFlag, row, col);
        }
        map[row][col] = 2;
    }
    this.invalidate();
    return super.onTouchEvent(event);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    if (map == null) {
        return;
    }
    Paint paint = new Paint();
    paint.setAntiAlias(true);
    paint.setColor(Color.BLUE);
    paint.setStrokeWidth(5);
    paint.setStyle(Paint.Style.STROKE);
    for (int i = 0; i < map.length; i++) {
        for (int j = 0; j < map[i].length; j++) {
            if (map[i][j] == 0) {
                Bitmap bm = BitmapFactory.decodeResource(this.getResources(), R.drawable.route);
                canvas.drawBitmap(bm, j * 80, i * 80, paint);
            } else if (map[i][j] == 1) {
                Bitmap bm = BitmapFactory.decodeResource(this.getResources(), R.drawable.wall);
                canvas.drawBitmap(bm, j * 80, i * 80, paint);
            } else if (map[i][j] == 2) {
                Bitmap bm = BitmapFactory.decodeResource(this.getResources(), R.drawable.path);
                canvas.drawBitmap(bm, j * 80, i * 80, paint);
            }
        }
    }
    if (path != null) {
        canvas.drawPath(path, paint);
    }

}


public interface OnTouchListener {
    void onTouchPoint(int type, int row, int col);
}
}