如何在我的“传入”类中生成随机的“传入障碍”？

Question

我试图每0.5秒使随机对象在屏幕上显示为障碍物。我该怎么做才能做到这一点？

我创建了一个“传入”类，以创建该类的不同对象，并每500毫秒将它们添加到“障碍”中。我向其中添加了draw方法，并尝试为每个对象调用它，以便它们向播放器移动。

进来的班级

package com.example.neonrace;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Rect;

class incoming {
    int top;
    int left;
    int right;
    int bttm;
    Rect carr;
    Bitmap incom;
    Context context;


    public incoming(int top, int left, int right, int bttm, Rect carr) 
{
        this.top = top;
        this.left = left;
        this.right = right;
        this.bttm = bttm;
        this.carr = carr;
        this.incom = incom;
        this.context = context;
}

    public void draw(Canvas canvas){
        incom = BitmapFactory.decodeResource(context.getResources(), 
R.drawable.inc);
        Rect carr = new Rect(this.left, this.top, this.right, 
this.bttm);
        canvas.drawBitmap(incom, null, carr, null);
        if (GameView.r == 0) {
            this.top = 0;
            this.left = GameView.RoadLeft;
            this.right = (GameView.DWidth * 4) / 10;
            this.bttm = (int) ((GameView.DHeight * 1.5) / 10);
            this.top = this.top + GameView.speed;
            this.bttm = this.bttm + GameView.speed;
        }
        else if (GameView.r == 1) {
            this.top = 0;
            this.left = GameView.DWidth * 4 / 10;
            this.right = GameView.DWidth * 5 / 10;
            this.bttm = (int) ((GameView.DHeight * 1.5) / 10);
            this.top = this.top + GameView.speed;
            this.bttm = this.bttm + GameView.speed;
        }
        else if (GameView.r == 2){
            this.top = 0;
            this.left = GameView.DWidth * 5 / 10;
            this.right = (GameView.DWidth * 6 / 10);
            this.bttm = (int) ((GameView.DHeight * 1.5) / 10);
            this.top = this.top + GameView.speed;
            this.bttm = this.bttm + GameView.speed;
        }
        else {
            this.top = 0;
            this.left = GameView.DWidth * 6 / 10;
            this.right = GameView.DWidth * 7 / 10;
            this.bttm = (int) ((GameView.DHeight * 1.5) / 10);
            this.top = this.top + GameView.speed;
            this.bttm = this.bttm + GameView.speed;
        }
    }

}

主GameView

package com.example.neonrace;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.Rect;
import android.os.Handler;
import android.view.Display;
import android.view.MotionEvent;
import android.view.View;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.Timer;
import java.util.TimerTask;

public class GameView extends View {

    public static int r;
    public static int RoadLeft;
    public static int DWidth;
    public static int DHeight;
    public static int speed;
    Handler handler;
    Runnable runnable;
    final int UpdateMS = 30;
    Bitmap background;
    Bitmap car;
    Display display;
    Point point;
    Rect rect;
    Rect road;
    Rect rcar;
    int  RoadRight;
    int Carleft, Carright, Carup;
    Paint paint;
    int topRoad = -1000000;
    int downRoad ;
    int score ;
    Random random;
    List obstacles = new ArrayList<incoming>();
    int NumOfObst;
    Timer timer = new Timer();
    int i;
    Canvas canvas;

    public GameView(Context context) {
        super(context);
        handler = new Handler();
        runnable = new Runnable() {
            @Override
            public void run() {
                invalidate();
            }
        };
        background = 
BitmapFactory.decodeResource(getResources(),R.drawable.grass);
        car = BitmapFactory.decodeResource(getResources(), 
R.drawable.enzo);
        display = 
((Activity)getContext()).getWindowManager().getDefaultDisplay();
        point = new Point();
        display.getSize(point);
        DWidth = point.x;
        DHeight = point.y;
        speed = 15;
        RoadLeft = point.x * 3 / 10;
        RoadRight = point.x * 7 / 10;
        Carleft = point.x * 5 / 10;
        Carright = point.x * 6 / 10;
        Carup = point.y * 7 / 10;
        rect = new Rect(0,0,DWidth,DHeight);
        paint  = new Paint();
        paint.setColor(Color.BLACK);
        Random random = new Random();
        int r = random.nextInt(5);


    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        canvas.drawBitmap(background, null, rect, null);

        topRoad = topRoad + speed;
        downRoad = downRoad + DHeight/2 + speed;

        road = new Rect(RoadLeft, topRoad, RoadRight,downRoad);
        canvas.drawRect(road, paint);

        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                obstacles.add(incoming);
            }
        },500);

        NumOfObst = obstacles.size();

        for (i = 0; i <= NumOfObst; i++){
            obstacles.get(i).draw(Canvas);
        }



        rcar = new Rect(Carleft, Carup, Carright, DHeight*9/10);
        canvas.drawBitmap(car,null,rcar,null);
        handler.postDelayed(runnable,UpdateMS);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        int tchx = (int) event.getX();
        if (action == MotionEvent.ACTION_DOWN){
            if (tchx < DWidth/2){
                Carleft = Carleft - (DWidth / 10);
                Carright = Carright - (DWidth / 10);
            }
            else {
                Carleft = Carleft + (DWidth / 10);
                Carright = Carright + (DWidth / 10);
            }
        }

        return true;
    }
    }

我希望随机物体会进入玩家的视野，但实际上我得到一个错误，我不知道如何解决。