试图制作一个寻宝游戏，但有一个问题与surview脚本

Question

一般的想法是允许用户点击字段并查找项目的应用程序。项目定义来自excel文件。物品将以随机位置散布在整个场地上。当用户点击屏幕时，它将创建漏洞。按下库存按钮时，找到的项目将显示在列表中。我在使用DrawSurface脚本时遇到问题。

xml：

    <android:layout_width="fill_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:id="@+id/mField" />

    <LinearLayout
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="50dp">

    <Button
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="0.5"
    android:text="View Inventory"
    android:id="@+id/btnInventory"/>

    <Button
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="0.5"
    android:text="Credits"
    android:id="@+id/btnCredits"/>

    </LinearLayout>

    </LinearLayout>

MainActivity：

    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.View;
    import android.app.AlertDialog;
    import android.content.DialogInterface;
    import java.io.BufferedReader;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.util.ArrayList;


    public class MainActivity extends AppCompatActivityimplementsView.OnClickListener {

    ArrayList<Item> inv = DrawSurface.getInventory();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    findViewById(R.id.btnInventory).setOnClickListener(this);
    findViewById(R.id.btnCredits).setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
    if (view.getId() == R.id.btnCredits) {
        AlertDialog.Builder dialog = new AlertDialog.Builder(this);
        dialog.setTitle("Made by");
        dialog.setMessage("DJon Archer" + "\nMGMS | CSE\n08/10/2017");
        dialog.setPositiveButton(" OK ", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int id) {
                dialog.dismiss();
            }

        });
        dialog.show();

    }
    else if (view.getId() == R.id.btnInventory)
    {
        loadItems();
    }

    }

    private ArrayList<Item> loadItems()
    {


    InputStream input = getResources().openRawResource(R.raw.items);
    BufferedReader reader = null;
    ArrayList<Item> items = new ArrayList<Item>();
    String line;

    try
    {
        reader = new BufferedReader(new InputStreamReader(input));
        while ((line = reader.readLine()) !=null)
        {
            items.add(new Item(line));
        }
    }
    catch (Exception e)
    {
        Log.e("MainActivity", "Reading list of Items failed!", e);
    }
    finally
    {
        try {
            if (reader != null) reader.close();
        }
        catch (Exception e)
        {
            Log.e("MainActivity", "Error closing file reader.", e);
        }
    }
    return items;
    }
    }

档案：

    public class Item {

    public String name;
    public int x;
    public int y;

    //constructor

    public Item(String n) {
     name = n;
    }
    }

DrawSurface：

    import android.content.Context;
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.graphics.Canvas;
    import android.util.AttributeSet;
    import android.util.Log;
    import android.view.MotionEvent;
    import android.view.SurfaceHolder;uu
    import android.view.SurfaceView;
    import android.view.View;
    import java.io.BufferedReader;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.util.ArrayList;


    abstract class DrawSurface extends SurfaceView implements SurfaceHolder.Callback, View.OnTouchListener
    {
    SurfaceHolder holder;
    Bitmap mBMPField;
    Bitmap mBMPHole;


    private static ArrayList<Item> mItems;

    public DrawSurface(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);

    // Getting the holder
    holder = getHolder();
    holder.addCallback(this);
    setOnTouchListener(this);
    findViewById(R.id.mField);
    }

    int radius = Math.max(mBMPHole.getHeight(),mBMPHole.getWidth()) / 2;

    public static ArrayList<Item> getInventory() {
    //called from MainActivity.java
    return mItems;
    }


    @Override
    public boolean onTouch(View v, MotionEvent event) {
    if(event.getAction()== MotionEvent.ACTION_DOWN)
    {
      for (int i=mItems.size()-1; i>0; i--)
         mItems.get(i);

        dx = mItems.x - center.x;
        dy = mItems.y - center.y;

        if((dx)*(dx) + (dy)*(dy) < radius*radius)
        {
            mItems.remove(i);

        }

     }

     setWillNotDraw(false);
     }

     //Surface holder allows to control and monitor the surface

     @Override
     public void surfaceCreated(SurfaceHolder holder)
     {

     Canvas c = holder.lockCanvas();

     if (c!=null) mField.Dim.set(0,0, c.getWidth(),c.getHeight());
     holder.unlockCanvasAndPost(c);
     invalidate();

     for (int i=0; i<mItems.size(); i++)
     {
        mItems.get(i).x = (int)(Math.random() * (float)mFieldDim.width());
        mItems.get(i).y = (int)(Math.random() * (float)mFieldDim.height());
     }

     }

     @Override
     public void onDraw(Canvas canvas)
     {
     drawBitmap();
     }

     void drawBitmap()
     {
     mBMPField = BitmapFactory.decodeResource(getResources(), R.drawable.field);
     mBMPHole = BitmapFactory.decodeResource(getResources(), R.drawable.hole);

     }
     }