用canvas畫的圖片跟在圖片上寫字居中的問題？

package cn.kevinmoto.View;

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.Rect;

import android.os.Bundle;
import android.util.DisplayMetrics;

import android.view.View;

public class MainActivity extends Activity {
  private int displayWidth;
  private int displayHeight;

   
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new M(this));
      

       
    }
    public class M extends View {
     public M(Context context){
      super(context);
      
      
     }
   
      public void onDraw(Canvas canvas) {
      super.onDraw(canvas);
      Paint paint = new Paint();
      
      paint.setAntiAlias(true);
      canvas.drawColor(Color.BLUE);
         DisplayMetrics dm = new DisplayMetrics();
      getWindowManager().getDefaultDisplay().getMetrics(dm);
      displayWidth = dm.widthPixels;
      displayHeight = dm.heightPixels;
    
     
    Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.menubar);

    Bitmap btm = BitmapFactory.decodeResource(getResources(), R.drawable.menutitle);
    
    int bitmapWidth = bitmap.getWidth();
    int bitmapHeight = bitmap.getHeight();
    
    

       canvas.drawBitmap(bitmap, (displayWidth-bitmapWidth)/2  , (displayHeight-bitmapHeight)/2, paint);
    canvas.drawBitmap(bitmap, (displayWidth-bitmapWidth)/2, (displayHeight-bitmapHeight)/2-bitmapHeight, paint);
    canvas.drawBitmap(bitmap, (displayWidth-bitmapWidth)/2, (displayHeight-bitmapHeight)/2-bitmapHeight-bitmapHeight, paint);
    canvas.drawBitmap(bitmap, (displayWidth-bitmapWidth)/2, (displayHeight-bitmapHeight)/2-bitmapHeight-bitmapHeight-bitmapHeight, paint);
    
    canvas.drawBitmap(btm, (displayWidth-bitmapWidth)/2, (displayHeight-bitmapHeight)/2-bitmapHeight-bitmapHeight-bitmapHeight-bitmapHeight, paint);
   //字體設置
    paint.setTextSize(20);  
          paint.setColor(Color.BLACK);// 
         
          //得到字符串的長度
          String writestr = "bitmap解決了";
          int iWordWidth = (int) paint.measureText(writestr);
       //(左，上，右，底)
          Rect rect = new Rect((displayWidth-bitmapWidth)/2,(displayHeight-bitmapHeight)/2,
            (displayWidth-bitmapWidth)/2+bitmapWidth,(displayHeight-bitmapHeight)/2+bitmapHeight);
          Rect rect1 = new Rect((displayWidth-bitmapWidth)/2,(displayHeight-bitmapHeight)/2,
            (displayWidth-bitmapWidth)/2+bitmapWidth,(displayHeight-bitmapHeight)/2-bitmapHeight+bitmapHeight);
          Rect rect2 = new Rect((displayWidth-bitmapWidth)/2,(displayHeight-bitmapHeight)/2,
            (displayWidth-bitmapWidth)/2+bitmapWidth,(displayHeight-bitmapHeight)/2-bitmapHeight-bitmapHeight+bitmapHeight);
          Rect rect3 = new Rect((displayWidth-bitmapWidth)/2,(displayHeight-bitmapHeight)/2,
            (displayWidth-bitmapWidth)/2+bitmapWidth,(displayHeight-bitmapHeight)/2-bitmapHeight-bitmapHeight-bitmapHeight+bitmapHeight);
//字體居中
    canvas.drawText(writestr, (rect.left + rect.right) / 2 - (iWordWidth) / 2, (rect.top + rect.bottom) / 2 + 20 / 2 , paint);
    canvas.drawText(writestr, (rect1.left + rect1.right) / 2 - (iWordWidth) / 2, (rect1.top + rect1.bottom) / 2 -20 / 2, paint);
    canvas.drawText(writestr,  (rect2.left + rect2.right) / 2 - (iWordWidth) / 2, (rect2.top + rect2.bottom) / 2 -60 / 2 , paint);
    canvas.drawText(writestr,(rect3.left + rect3.right) / 2 - (iWordWidth) / 2, (rect3.top + rect3.bottom) / 2 -100 / 2 , paint);

  
      
     }
    }
   
}