如何将此矩形和图像置于y轴中心？

Question

到目前为止，我的图像从0,0开始并正确缩放。它下面有一个黑色的酒吧。如何对齐它以使其沿y居中，图像上方和下方有黑条？

编辑：同样，什么是“this.getWidth（），this.getHeight（）”指的是当我将对象设为“dest”时 - mBitmap的宽度？文档确实说它们代表了视图的宽度，我只是想确保我认为它是正确的mBitmap。

public class SpotGameActivity extends Activity {

private Bitmap mBitmap;

/** Called when the activity is first created. */


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.dpi2b);
    setContentView(new BitMapView(this, mBitmap));

}

class BitMapView extends View {
    Bitmap mBitmap = null;

    public BitMapView(Context context, Bitmap bm) {
        super(context);
        mBitmap = bm;
    }

    @Override
    protected void onDraw(Canvas canvas) {


        //DisplayMetrics metrics = new DisplayMetrics();
        //getWindowManager().getDefaultDisplay().getMetrics(metrics);

        // called when view is drawn
        Paint paint = new Paint();
        paint.setFilterBitmap(true);
        // The image will be scaled so it will fill the width, and the
        // height will preserve the image’s aspect ration
        float aspectRatio = ((float) mBitmap.getWidth()) / mBitmap.getHeight();
        Rect dest = new Rect(0, 0, this.getWidth(),(int) (this.getWidth() / aspectRatio));
        String AR = Double.toString(aspectRatio);
        canvas.drawBitmap(mBitmap, null, dest, paint);
        Toast.makeText(SpotGameActivity.this, AR, Toast.LENGTH_SHORT).show();   
    }

我现在已经看到了视图大小和图像大小之间的差异。我把差异除以2但是现在，我的图像对齐到屏幕的底部而不是y轴的中间。任何提示？：

@Override
    protected void onDraw(Canvas canvas) {


        DisplayMetrics metrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(metrics);
        int scrHeight = this.getHeight();
        String sH = Integer.toString(scrHeight);
        Log.v(TAG, "scrHeight =" + sH );
        int imgHeight= mBitmap.getHeight();
        String iH = Integer.toString(imgHeight);
        Log.v(TAG, "imgHeight =" + iH );

        int diff = scrHeight - imgHeight;
        String dif = Integer.toString(diff);
        Log.v(TAG, "diff =" + dif );


        int dvd= diff/2;

        // called when view is drawn
        Paint paint = new Paint();
        paint.setFilterBitmap(true);
        // The image will be scaled so it will fill the width, and the
        // height will preserve the image’s aspect ration
        float aspectRatio = ((float) mBitmap.getWidth()) / mBitmap.getHeight();

        Rect dest = new Rect(0, dvd, this.getWidth(),(int) (this.getWidth() / aspectRatio)+dvd);
        String AR = Double.toString(dvd);

        canvas.drawBitmap(mBitmap, null, dest, paint);

        Toast.makeText(SpotGameActivity.this, AR, Toast.LENGTH_SHORT).show();