2011.09.29（2）——— android 图片缩略图-优快云博客

本文介绍了Android中图片缩略图的实现方法，包括使用BitmapUtil工具类进行图片尺寸调整和查询图片缩略图等功能。
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2011.09.29（2）——— android 图片缩略图

参考：[url]http://www.eoeandroid.com/thread-101021-1-1.html[/url]

前面我们说过视频缩略图的做法今天看一下图片的缩略图获得直接上代码一个工具类
package com.lp;

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.provider.MediaStore;

public final class BitmapUtil {
	public static Bitmap decodeBitmap(String path, int displayWidth, int displayHeight) {
		BitmapFactory.Options op = new BitmapFactory.Options();
		op.inJustDecodeBounds = true;
		// op.inJustDecodeBounds = true;表示我们只读取Bitmap的宽高等信息，不读取像素。
		Bitmap bmp = BitmapFactory.decodeFile(path, op); // 获取尺寸信息
		// op.outWidth表示的是图像真实的宽度
		// op.inSamplySize 表示的是缩小的比例
		// op.inSamplySize = 4,表示缩小1/4的宽和高，1/16的像素，android认为设置为2是最快的。
		// 获取比例大小
		int wRatio = (int) Math.ceil(op.outWidth / (float) displayWidth);
		int hRatio = (int) Math.ceil(op.outHeight / (float) displayHeight);
		// 如果超出指定大小，则缩小相应的比例
		if (wRatio > 1 && hRatio > 1) {
			if (wRatio > hRatio) {
				// 如果太宽，我们就缩小宽度到需要的大小，注意，高度就会变得更加的小。
				op.inSampleSize = wRatio;
			} else {
				op.inSampleSize = hRatio;
			}
		}
		op.inJustDecodeBounds = false;
		bmp = BitmapFactory.decodeFile(path, op);
		return Bitmap.createScaledBitmap(bmp, displayWidth, displayHeight, true);
		// Bitmap.createScaledBitmap(Bitmap src,int detWidth,int detHeight,boolean filter)
		// 从原Bitmap创建一个给定宽高的Bitmap
	}

	/**
	 * * 采用复杂计算来决定缩放 *
	 * 
	 * @param path
	 *            *
	 * @param maxImageSize
	 *            *
	 * @return
	 */
	public static Bitmap decodeBitmap(String path, int maxImageSize) {
		BitmapFactory.Options op = new BitmapFactory.Options();
		op.inJustDecodeBounds = true;
		Bitmap bmp = BitmapFactory.decodeFile(path, op);
		// 获取尺寸信息
		int scale = 1;
		if (op.outWidth > maxImageSize || op.outHeight > maxImageSize) {
			// Math.pow(double a, double b)表示返回第一个参数的第二个参数的次幂
			// Math.log（double a）返回double的自然对数,底数是e
			// Math.round(double e)返回最接近double的值
			scale = (int) Math.pow(2, (int) Math.round(Math.log(maxImageSize / (double) Math.max(op.outWidth, op.outHeight)) / Math.log(0.5)));
		}
		op.inJustDecodeBounds = false;
		op.inSampleSize = scale;
		bmp = BitmapFactory.decodeFile(path, op);
		return bmp;
	}

	public static Cursor queryThumbnails(Activity context) {
		String[] columns = new String[] {
		// Thumbnails表示的缩略图的意思
				MediaStore.Images.Thumbnails.DATA, MediaStore.Images.Thumbnails._ID, MediaStore.Images.Thumbnails.IMAGE_ID };
		return context.managedQuery(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, columns, null, null, MediaStore.Images.Thumbnails.DEFAULT_SORT_ORDER);
	}

	public static Cursor queryThumbnails(Activity context, String selection, String[] selectionArgs) {
		String[] columns = new String[] { MediaStore.Images.Thumbnails.DATA, MediaStore.Images.Thumbnails._ID, MediaStore.Images.Thumbnails.IMAGE_ID };
		// public final Cursor managedQuery (Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder)
		// uri The URI of the content provider to query.
		// projection List of columns to return.
		// selection SQL WHERE clause.
		// selectionArgs The arguments to selection, if any ?s are pesent
		// sortOrder SQL ORDER BY clause.
		return context.managedQuery(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, columns, selection, selectionArgs, MediaStore.Images.Thumbnails.DEFAULT_SORT_ORDER);
	}

	// 通过缩略图的ID来查询
	public static Bitmap queryThumbnailById(Activity context, int thumbId) {
		String selection = MediaStore.Images.Thumbnails._ID + " = ?";
		String[] selectionArgs = new String[] { thumbId + "" };
		Cursor cursor = BitmapUtil.queryThumbnails(context, selection, selectionArgs);
		if (cursor.moveToFirst()) {
			String path = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails.DATA));
			cursor.close();
			return BitmapUtil.decodeBitmap(path, 100, 100);
		} else {
			cursor.close();
			return null;
		}
	}

	public static Bitmap[] queryThumbnailsByIds(Activity context, Integer[] thumbIds) {
		Bitmap[] bitmaps = new Bitmap[thumbIds.length];
		for (int i = 0; i < bitmaps.length; i++) {
			bitmaps[i] = BitmapUtil.queryThumbnailById(context, thumbIds[i]);
		}
		return bitmaps;
	}

	/**
	 * * 获取全部
	 * 
	 * *
	 * 
	 * @param context
	 *            * @return
	 * 
	 * */
	public static List<Bitmap> queryThumbnailList(Activity context) {
		List<Bitmap> bitmaps = new ArrayList<Bitmap>();
		Cursor cursor = BitmapUtil.queryThumbnails(context);
		for (int i = 0; i < cursor.getCount(); i++) {
			cursor.moveToPosition(i);
			String path = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails.DATA));
			Bitmap b = BitmapUtil.decodeBitmap(path, 100, 100);
			bitmaps.add(b);
		}
		cursor.close();
		return bitmaps;
	}

	public static List<Bitmap> queryThumbnailListByIds(Activity context, int[] thumbIds) {
		List<Bitmap> bitmaps = new ArrayList<Bitmap>();
		for (int i = 0; i < thumbIds.length; i++) {
			Bitmap b = BitmapUtil.queryThumbnailById(context, thumbIds[i]);
			bitmaps.add(b);
		}
		return bitmaps;
	}

	public static Cursor queryImages(Activity context) {
		String[] columns = new String[] { MediaStore.Images.Media._ID, MediaStore.Images.Media.DATA, MediaStore.Images.Media.DISPLAY_NAME };
		return context.managedQuery(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, columns, null, null, MediaStore.Images.Media.DEFAULT_SORT_ORDER);
	}

	public static Cursor queryImages(Activity context, String selection, String[] selectionArgs) {
		String[] columns = new String[] { MediaStore.Images.Media._ID, MediaStore.Images.Media.DATA, MediaStore.Images.Media.DISPLAY_NAME };
		return context.managedQuery(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, columns, selection, selectionArgs, MediaStore.Images.Media.DEFAULT_SORT_ORDER);
	}

	public static Bitmap queryImageById(Activity context, int imageId) {
		String selection = MediaStore.Images.Media._ID + "=?";
		String[] selectionArgs = new String[] { imageId + "" };
		Cursor cursor = BitmapUtil.queryImages(context, selection, selectionArgs);
		if (cursor.moveToFirst()) {
			String path = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA));
			cursor.close();
			// return BitmapUtills.decodeBitmap(path, 260, 260);
			return BitmapUtil.decodeBitmap(path, 220);
			// 看看和上面这种方式的差别,看了，差不多
		} else {
			cursor.close();
			return null;
		}
	}

	/**
	 * * 根据缩略图的Id获取对应的大图 *
	 * 
	 * @param context
	 *            *
	 * @param thumbId
	 *            *
	 * @return
	 * */
	public static Bitmap queryImageByThumbnailId(Activity context, Integer thumbId) {
		String selection = MediaStore.Images.Thumbnails._ID + " = ?";
		String[] selectionArgs = new String[] { thumbId + "" };
		Cursor cursor = BitmapUtil.queryThumbnails(context, selection, selectionArgs);
		if (cursor.moveToFirst()) {
			int imageId = cursor.getInt(cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails.IMAGE_ID));
			cursor.close();
			return BitmapUtil.queryImageById(context, imageId);
		} else {
			cursor.close();
			return null;
		}
	}

}