加载大图片

[android]代码库

import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

public class LoadBitmapUtils {

	public static Bitmap decodeSampledBitmapFromResource(Resources res,
			int resId, int reqWidth, int reqHeight) {

		// First decode with 'inJustDecodeBounds=true' to check dimensions
		final BitmapFactory.Options options = new BitmapFactory.Options();
		options.inJustDecodeBounds = true;
		BitmapFactory.decodeResource(res, resId, options);

		// Calculate inSampleSize
		options.inSampleSize = calculateInSampleSize(options, reqWidth,
				reqHeight);

		// Decode bitmap with inSampleSize set
		options.inJustDecodeBounds = false;
		return BitmapFactory.decodeResource(res, resId, options);
	}

	/**
	 * 计算需要缩放的比例
	 * 
	 * @param options
	 * @param reqWidth
	 * @param reqHeight
	 * @return int 算最大insamplesize值是2的幂
	 */
	public static int calculateInSampleSize(BitmapFactory.Options options,
			int reqWidth, int reqHeight) {
		// Raw height and width of image
		final int height = options.outHeight;
		final int width = options.outWidth;
		/***
		 * 缩放比例，默认值是1（不缩放）
		 */
		int inSampleSize = 1;

		if (height > reqHeight || width > reqWidth) {

			final int halfHeight = height / 2;
			final int halfWidth = width / 2;

			// Calculate the largest inSampleSize value that is a power of 2 and
			// keeps both
			// height and width larger than the requested height and width.
			// 计算最大insamplesize值是2的幂，同时保持高度和宽度大于所要求的高度和宽度。
			while ((halfHeight / inSampleSize) > reqHeight
					&& (halfWidth / inSampleSize) > reqWidth) {
				inSampleSize *= 2;
			}
		}

		return inSampleSize;
	}
}