问安卓游戏在启动MatheGame活动后崩溃

EN

import android.graphics.Point;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Display;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowManager;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.Timer;
import java.util.TimerTask;

public class MatheGame extends AppCompatActivity {

private TextView scoreLabel;
private TextView startLabel;
private ImageView box;
ImageView orange;

// Size
private int frameHeight;
private int boxSize;
private int screenWidth;
private int screenHeight;

// Position
private int boxY;
private int orangeX;
private int orangeY;

// Speed
private int boxSpeed;
private int orangeSpeed;


// Score
private int score = 0;


// Initialize Class
private Handler handler = new Handler();
private Timer timer = new Timer();


// Status Check
private boolean action_flg = false;
private boolean start_flg = false;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    scoreLabel = (TextView) findViewById(R.id.scoreLabel);
    startLabel = (TextView) findViewById(R.id.startLabel);
    box = (ImageView) findViewById(R.id.box);
    orange = (ImageView)findViewById(R.id.orange);


    // Get screen size.
    WindowManager wm = getWindowManager();
    Display disp = wm.getDefaultDisplay();
    Point size = new Point();
    disp.getSize(size);

    screenWidth = size.x;
    screenHeight = size.y;


    boxSpeed = Math.round(screenHeight / 60);
    orangeSpeed = Math.round(screenWidth / 60);

    orange.setX(-80);
    orange.setY(-80);


    scoreLabel.setText("Score : 0");

}


public void changePos() {

    hitCheck();

    // Orange
    orangeX -= orangeSpeed;
    if (orangeX < 0) {
        orangeX = screenWidth + 20;
        orangeY = (int) Math.floor(Math.random() * (frameHeight - orange.getHeight()));
    }
    orange.setX(orangeX);
    orange.setY(orangeY);


    // Move Box
    if (action_flg == true) {
        // Touching
        boxY -= boxSpeed;
    } else {
        // Releasing
        boxY += boxSpeed;
    }
    // Check box position.
    if (boxY < 0) boxY = 0;
    if (boxY > frameHeight - boxSize) boxY = frameHeight - boxSize;
    box.setY(boxY);
    scoreLabel.setText("Score : " + score);
}


public void hitCheck() {

    // Orange
    int orangeCenterX = orangeX + orange.getWidth() / 2;
    int orangeCenterY = orangeY + orange.getHeight() / 2;

    if (0 <= orangeCenterX && orangeCenterX <= boxSize &&
            boxY <= orangeCenterY && orangeCenterY <= boxY + boxSize) {
        score += 10;
        orangeX = -10;
    }

}

public boolean onTouchEvent(MotionEvent me) {


    if (start_flg == false) {
        start_flg = true;


        FrameLayout frame = (FrameLayout) findViewById(R.id.frame);
        frameHeight = frame.getHeight();
        boxY = (int)box.getY();
        boxSize = box.getHeight();



        startLabel.setVisibility(View.GONE);


        timer.schedule(new TimerTask() {

            @Override

            public void run() {

                handler.post(new Runnable() {
                    @Override
                    public void run() {
                        changePos();
                    }

                });

            }

        }, 0, 20);

    } else {

        if (me.getAction() == MotionEvent.ACTION_DOWN) {

            action_flg = true;

        } else if (me.getAction() == MotionEvent.ACTION_UP) {

            action_flg = false;
        }
    }
    return true;
}

@Override
public boolean dispatchKeyEvent(KeyEvent event) {

    if (event.getAction() == KeyEvent.ACTION_DOWN) {
        switch (event.getKeyCode()) {

            case KeyEvent.KEYCODE_BACK:
                return true;
        }
    }
    return super.dispatchKeyEvent(event);
}

}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.eitisoft.mathetrainer.MatheGame">

<TextView
    android:id="@+id/scoreLabel"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:text="Score : 300"
    android:textSize="18sp"
    android:paddingLeft="10dp"
    android:gravity="center_vertical"/>

<FrameLayout
    android:id="@+id/frame"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/startLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Tap to Start"
        android:textSize="30sp"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="130dp"/>

    <ImageView
        android:id="@+id/box"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:src="@drawable/box"
        android:layout_gravity="center_vertical"/>

    <ImageView
        android:id="@+id/orange"
        android:layout_width="20dp"
        android:layout_height="20dp"
        android:src="@drawable/punkt"/>


</FrameLayout>


</RelativeLayout>

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setX(float)' on a null object reference
                                                 at com.eitisoft.mathetrainer.MatheGame.onCreate(MatheGame.java:85)