碰撞检测/从 ArrayList 中删除对象 [英] Collision Detection/Remove object from ArrayList
问题描述
我目前正在尝试测试下落物体和盒子之间的碰撞.我了解基本的碰撞检测，但我的问题是我必须测试它是否有无限数量的坠落物体.当这些对象(花)被创建时，它们被存储在一个 ArrayList 中.ArrayList 处理画布上对象的绘制(使用 for each 来更新位置).当一朵花被抓住"在盒子里时，我的问题就出现了.如何让它从屏幕上消失/从数组列表中删除而不发生空引用?我可以向你展示我到目前为止的逻辑......请让我知道你的想法.我真的被困住了，但感觉我离搞清楚这件事很近了.
I am currently trying to test collision between a falling object and a box. I understand basic collision detection, but my problem here is that I have to test it for an indefinite number of falling objects. When these objects(blossoms) are created, they are stored in an ArrayList. The ArrayList handles the drawing of the object on the canvas (using a for each to update the position). My problem comes when a blossom is "caught" in the box. How do I make it disappear from the screen/removed from the array list without a null reference happening? I can show you the logic I have so far...please let me know what you think. I am REALLY stuck, but feel like I'm so close to figuring this out.
开花班
public class Blossom{
private Bitmap blossom;
private int blossom_x = 0;
private int blossom_y = 0;
private int blossomWidth = 0;
private int blossomHeight = 0;
private boolean hit = false;
private Random generator = new Random();
RectF blossomRect;
private static final String TAG = "Debug";
public Blossom(Bitmap bitmap)
{
blossom = bitmap;
blossomWidth = blossom.getWidth();
blossomHeight = blossom.getHeight();
blossom_x = generator.nextInt(320-blossom.getWidth());
blossomRect = new RectF(blossom_x,blossom_y, blossom_x + blossomWidth, blossom_y + blossomHeight);
}
public Bitmap getBitmap()
{
return blossom;
}
public Boolean hit(int boxLeft, int boxTop, int boxRight,int boxBottom)
{
if(blossom_x > boxLeft & blossom_y > boxTop
& blossom_x + blossom.getWidth() < boxRight
& blossom_y + blossom.getHeight() < boxBottom)
{
Log.v(TAG, "Collision Detected");
return true;
}
else
{
return false;
}
}
public float getBlossomX()
{
return blossom_x;
}
public float getBlossomY()
{
return blossom_y;
}
public float getBlossomWidth()
{
return blossomWidth;
}
public float getBlossomHeight()
{
return blossomHeight;
}
public void Draw(Canvas canvas)
{
//draws the flower falling
if (hit == false)
{
canvas.drawBitmap(blossom, blossom_x,
blossom_y = blossom_y+5 , null);
}
}
public void UpdatePosition()
{
blossomRect.set(blossom_x, blossom_y, blossom_x + 25, blossom_y + 25);
}
}
板视图
public class BoardView extends SurfaceView implements SurfaceHolder.Callback{
Context mContext;
Bitmap box =
(BitmapFactory.decodeResource
(getResources(), R.drawable.box));
private BoardThread thread;
private int box_x = 140;
private int box_y = 378;
private int boxWidth = box.getWidth();
private int boxHeight = box.getHeight();
private ArrayList<Blossom> blossomArrayList = new ArrayList<Blossom>();
private int blossomNum = 0;
private String score;
private int currentScore = 0;
Thread timer;
boolean mode = false;
boolean game = false;
private static final String TAG = "Debug";
final Paint scorePaint = new Paint();
public BoardView(Context context){
super(context);
scorePaint.setColor(Color.BLACK);
scorePaint.setTextSize(12);
scorePaint.setTypeface(Typeface.MONOSPACE);
//surfaceHolder provides canvas that we draw on
getHolder().addCallback(this);
// controls drawings
thread = new BoardThread(getHolder(),this, blossomArrayList, box_x, box_y,
boxWidth, boxHeight);
timer = new Thread(){
public void run(){
//makes sure the player still has 3 lives left
while(game == false){
uiCallback.sendEmptyMessage(0);
try {
Thread.sleep(2000); // wait two seconds before drawing the next flower
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} //sleep for 2 seconds
}
}
};
timer.start();
//intercepts touch events
setFocusable(true);
}
@Override
public void onDraw(Canvas canvas){
canvas.drawColor(Color.WHITE);
score = "SCORE: " + currentScore;
//note: pay attention to order you draw things
//don't change order or else blossoms will fall
//on top of box, not "into" it.
//display the scoreboard
canvas.drawText(score,240,420,scorePaint);
//draw box and set start location
for(Blossom blossom: blossomArrayList) // getting errors here
{
blossom.Draw(canvas);
blossom.hit(box_x,box_y, box_x + boxWidth, box_y + boxHeight);
}
canvas.drawBitmap(box, box_x, box_y, null);
}
@Override
public boolean onTouchEvent(MotionEvent event){
//handles movement of box
if(event.getAction() == MotionEvent.ACTION_DOWN){
if(event.getX() > box_x & event.getY() > box_y &
event.getX() < box_x + boxWidth & event.getY() < box_y + boxHeight)
{
mode = true;
}
}
if(event.getAction() == MotionEvent.ACTION_MOVE) {
if(event.getX() > box_x & event.getY() > box_y &
event.getX() < box_x + boxWidth & event.getY() < box_y + boxHeight)
{
mode = true;
}
if(mode == true){
box_x = (int)event.getX();
}
}
if(event.getAction() == MotionEvent.ACTION_UP){
mode = false;
}
invalidate();
return true;
}
@Override
public void surfaceChanged(SurfaceHolder holder,
int format, int width, int height ){
Log.v(TAG, "Surface Changed");
//somehow these don't seem to be working
}
@Override
public void surfaceCreated(SurfaceHolder holder){
thread.startRunning(true);
thread.start();
}
@Override
public void surfaceDestroyed(SurfaceHolder holder){
Log.v(TAG, "Surface Destroyed");
//somehow these don't seem to be working
thread.startRunning(false);
thread.stop();
timer.interrupt();
timer.stop();
}
private Handler uiCallback = new Handler(){
public void handleMessage(Message msg){
//add a new blossom to the blossom ArrayList!!
blossomArrayList.add(new Blossom(
(BitmapFactory.decodeResource
(getResources(), R.drawable.blossom))));
blossomNum++;
//remove neccesary blossoms from list
Log.v(TAG, "Number of Blossoms =" + blossomNum);
}
};
}
板线
public class BoardThread extends Thread {
private SurfaceHolder surfaceHolder;
private BoardView boardView;
private ArrayList<Blossom> blossomArrayList;
private int boxX;
private int boxY;
private int boxWidth;
private int boxHeight;
private boolean mrun =false;
public BoardThread(SurfaceHolder holder, BoardView boardView2,
ArrayList<Blossom> blossomArrayList1,
int box_x, int box_y, int boxW, int boxH) {
surfaceHolder = holder;
boardView=boardView2;
blossomArrayList = blossomArrayList1;
boxX = box_x;
boxY = box_y;
boxW = boxWidth;
boxH = boxHeight;
}
public void startRunning(boolean run) {
mrun=run;
}
@Override
public void run() {
super.run();
Canvas canvas;
while (mrun) {
canvas=null;
try {
canvas = surfaceHolder.lockCanvas(null);
synchronized (surfaceHolder) {
//test for collision
Collision(blossomArrayList, boxX, boxY, boxWidth, boxHeight);
// draw flowers
boardView.onDraw(canvas); // and getting errors here - concurrent
}
} finally {
if (canvas != null) {
surfaceHolder.unlockCanvasAndPost(canvas);
}
}
}
}
public void Collision(ArrayList<Blossom> blossomArrayList, int box_x, int box_y,
int boxWidth, int boxHeight)
{
for(Blossom blossom: blossomArrayList)
{
blossom.UpdatePosition();
if(blossom.hit(box_x,box_y, box_x + boxWidth, box_y + boxHeight) == true)
{
///if flower is caught, add to score
//currentScore += 100;
}
}
}
}
推荐答案
设置可见性标志是一种方法，但是我建议不要这样做，因为您要向 ArrayList 添加不确定数量的位图...会发现自己很快就会耗尽内存.将您的碰撞检测迭代器从 foreach 更改为手写循环，这将避免您在上面列出的代码中可能遇到的并发问题.
Setting a visibility flag is one way to go, however I'd recommend against it since you are adding an indeterminate amount of Bitmaps to an ArrayList...you'll find yourself running out of memory pretty quickly. Change your collision detection iterator from a foreach to a handwritten loop, this will avoid concurrency issues you may run to in the code you have listed above.
for (int i = 0; i < blossomArrayList.size(); i++)
{
if(blossom.hit(box_x,box_y, box_x + boxWidth, box_y + boxHeight)) {
blossomArrayList.remove(i);
}
}
此外，我建议您将所有 ArrayList foreach 迭代器更改为手写 for 循环，因为在 Android 上迭代 ArrayLists(但不是任何其他对象)相对较慢，并且可能导致意外的并发问题.
Additionally, I'd recommend changing all your ArrayList foreach iterators to hand written for loops, as iterating ArrayLists (but not any other object) is relatively slow on Android and can lead to unexpected concurrency issues.
第三，似乎您只需要在 UpdatePositions 循环完成后运行一次 Collision() 方法，因为您已经检查了 Collision() 方法中的每个 Blossom.
Thirdly, it seems as though you only need to run your Collision() method once after your UpdatePositions loop has completed since you're already checking every Blossom in your Collision() method.
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