Android开发之大位图二次採样压缩处理（源码分享）

图片有各种形状和大小。在很多情况下这些图片是远远大于我们的用户界面(UI)且占领着极大的内存空间，假设我们不正确位图进行压缩处理，我们的程序会发生内存泄露的错误。

MainActivity的代码

package com.example.g08_bitmap;

import android.os.Bundle;
import android.app.Activity;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.widget.ImageView;

public class MainActivity extends Activity {
	private ImageView imageView;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		imageView = (ImageView) this.findViewById(R.id.imageView1);
		imageView.setImageBitmap(decodeSampledBitmapFromResource(
				getResources(), R.drawable.a, 300, 300));
	}

	public static Bitmap decodeSampledBitmapFromResource(Resources res,
			int resId, int reqWidth, int reqHeight) {
		final BitmapFactory.Options options = new BitmapFactory.Options();
		//先将inJustDecodeBounds属性设置为true,解码避免内存分配
		options.inJustDecodeBounds = true;
		// 将图片传入选择器中
		BitmapFactory.decodeResource(res, resId, options);
		// 对图片进行指定比例的压缩
		options.inSampleSize = calculateInSampleSize(options, reqWidth,
				reqHeight);
		//待图片处理完毕后再进行内存的分配，避免内存泄露的发生
		options.inJustDecodeBounds = false;
		return BitmapFactory.decodeResource(res, resId, options);
	}

	// 计算图片的压缩比例
	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;
		int inSampleSize = 1;

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

			final int heightRatio = Math.round((float) height
					/ (float) reqHeight);
			final int widthRatio = Math.round((float) width / (float) reqWidth);
			// 选择长宽高较小的比例，成为压缩比例
			inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
		}
		return inSampleSize;
	}

}