Android绘制进阶之三：在位图上(Bitmap)绘制位图（Bitmap）

1，点击按钮，指定action和uri，设定结果码(ResultCode).到达手机默认相册的Gallery.

代码如下：

 

public void onClick(View v) {
        // TODO Auto-generated method stub
        Intent intent = new Intent(Intent.ACTION_PICK,
                android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);//启动照片Gallery
        startActivityForResult(intent, 0);
    }

2，选择图片，返回所选照片uri信息

代码如下：

 

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
        // TODO Auto-generated method stub
        super.onActivityResult(requestCode, resultCode, intent);

        if (resultCode == RESULT_OK) {//操作成功
            Uri imgFileUri = intent.getData();//获得所选照片的信息

 

3，处理图片，设定合适的尺寸（正好适应屏幕）

设定BitmapFactory.Options 参数inJustDecodeBounds = true，即不创建bitmap，但可获取bitmap的相关属性。以宽高比例差距 最大者为基准。

代码如下：

 

//由于返回的图像可能太大而无法完全加载到内存中。系统有限制，需要处理。
            Display currentDisplay = getWindowManager().getDefaultDisplay();
            int defaultHeight = currentDisplay.getHeight();
            int defaultWidth = currentDisplay.getWidth();

            BitmapFactory.Options bitmapFactoryOptions = new BitmapFactory.Options();
            bitmapFactoryOptions.inJustDecodeBounds = true;///只是为获取原始图片的尺寸，而不返回Bitmap对象
            //注上：If set to true, the decoder will return null (no bitmap), but the out... fields will still be set,
            //allowing the caller to query the bitmap without having to allocate the memory for its pixels
            try {
                Bitmap bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(imgFileUri), null, bitmapFactoryOptions);
                int outHeight = bitmapFactoryOptions.outHeight;
                int outWidth = bitmapFactoryOptions.outWidth;
                int heightRatio = (int) Math.ceil((float)outHeight/defaultHeight);
                int widthRatio = (int) Math.ceil((float)outWidth/defaultWidth);

                if (heightRatio > 1 || widthRatio >1) {
                    if (heightRatio > widthRatio) {
                        bitmapFactoryOptions.inSampleSize = heightRatio;
                    } else {
                        bitmapFactoryOptions.inSampleSize = widthRatio;
                    }
                }

4，inJustDecodeBounds = false，创建将此bitmap赋给第一个ImageView。

代码如下：

 

bitmapFactoryOptions.inJustDecodeBounds = false;
                bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(imgFileUri), null, bitmapFactoryOptions);

                mImageShow.setImageBitmap(bitmap);

5，绘制bitmap(选中的图片)，赋给第二个ImageView

代码如下：

 

/*
                 * 在位图上绘制位图
                 */

                Bitmap bitmapAltered = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());

                Canvas canvas = new Canvas(bitmapAltered);//bitmap提供了画布，只在此提供了大小尺寸，偏移后并未有背景显示出来


                Paint paint = new Paint();

                canvas.drawBitmap(bitmap, 0, 0, paint);//绘制的图片和之前的一模一样

                mImageAltered.setImageBitmap(bitmapAltered);