Android编程实现只显示图片一部分的方法

package com.iwin.zzs;import android.app.Activity;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Matrix;import android.os.Bundle;import android.util.DisplayMetrics;import android.view.WindowManager;public class ShowPoritionPictureActivity extends Activity {  /** Called when the activity is first created. */  Bitmap picRes;  Bitmap showPic;  //获取原图片的宽和高  int picWidth;  int picHeight;  private PoritionView poritonView = null;  @Override  public void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.main);    // 不显示状态栏    this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);    DisplayMetrics dm = new DisplayMetrics();    this.getWindowManager().getDefaultDisplay().getMetrics(dm);    // 得到屏幕的长和宽    int screenWidth = dm.widthPixels; //水平分辨率    int screenHeight = dm.heightPixels; //垂直分辨率    picRes = BitmapFactory.decodeResource(this.getResources(), R.drawable.girl);    // 得到图片的长和宽    picWidth = picRes.getWidth();    picHeight = picRes.getHeight();    // 计算缩放率，新尺寸除原始尺寸    float scaleWidth = ((float) screenWidth ) / picWidth;    float scaleHeight = ((float) screenHeight ) / picHeight;    // 创建操作图片用的matrix对象    Matrix matrix = new Matrix();    // 缩放图片动作    matrix.postScale(scaleWidth, scaleHeight);    // 新得到的图片是原图片经过变换填充到整个屏幕的图片    Bitmap picNewRes = Bitmap.createBitmap(picRes, 0, 0,picWidth, picHeight, matrix, true);    // bitmap = Bitmap.createBitmap(400, 480, Bitmap.Config.ARGB_8888);    // canvas=new Canvas();    // canvas.setBitmap(bitmap);    showPic = Bitmap.createBitmap(picNewRes, screenWidth/2-50, screenHeight/2-50, 100, 100);    poritonView = new PoritionView(this);    poritonView.setBitmapShow(showPic, screenWidth/2-50, screenHeight/2-50);    setContentView(poritonView);}

package com.iwin.zzs;import android.content.Context;import android.graphics.Bitmap;import android.graphics.Canvas;import android.view.View;public class PoritionView extends View {  private Bitmap showPic = null;  private int startX = 0;  private int startY = 0;  public PoritionView(Context context) {    super(context);    // TODO Auto-generated constructor stub  }  @Override  protected void onDraw(Canvas canvas) {    // TODO Auto-generated method stub    super.onDraw(canvas);    canvas.drawBitmap(showPic, startX, startY, null);  }  public void setBitmapShow(Bitmap b, int x, int y)  {    showPic = b;    startX = x;    startY = y;  }}