Android 獲得圖片並解碼成縮圖以減少記憶體消耗

標籤：android   des   style   blog   http   color   

本文內容

• 環境
• 示範

下載 Demo

環境

• Windows 2008 R2 64 位元
• Eclipse ADT V22.6.2，Android 4.4.3
• SAMSUNG GT-I9008L，Android OS 2.2.2

 

示範

縮圖能減少手機記憶體的消耗。網路上的資源一般對手機來說，大了點，把圖片解碼，減少其尺寸，從而減少手機記憶體的消耗。

本文採用的歌曲列表是 Android_Music_Demo_json_h_array.xml 檔案，雖然檔案尾碼名是 .xml，但內部其實是 JSON 格式，因為 cnblog 不讓上傳 .json 格式的檔案，該檔案裡的縮圖都較大，是 .jpg 格式，而與之對應的 Android_Music_Demo_json_array.xml 檔案裡的縮圖，都很小，都是才不到10k的 .png 格式。

圖 1

假設給定一個圖片連結地址，想獲得圖片縮圖，核心代碼如下所示，點擊此處下載：

private Bitmap getBitmap(String url) {

        File f = fileCache.getFile(url);

        // from SD cache

        Bitmap b = decodeFile(f);

        if (b != null)

            return b;

        // from web

        try {

            Bitmap bitmap = null;

            URL imageUrl = new URL(url);

            HttpURLConnection conn = (HttpURLConnection) imageUrl

                    .openConnection();

            conn.setRequestMethod("GET");

            // Sets the flag indicating whether this URLConnection allows input.

            // conn.setDoInput(true);

            conn.setConnectTimeout(3000);

            conn.setReadTimeout(3000);

            // Flag to define whether the protocol will automatically follow

            // redirects or not.

            conn.setInstanceFollowRedirects(true);

            int response_code = conn.getResponseCode();

            if (response_code == 200) {

                InputStream is = conn.getInputStream();

                OutputStream os = new FileOutputStream(f);

                StreamUtils.CopyStream(is, os);

                os.close();

                conn.disconnect();

                bitmap = decodeFile(f);

                return bitmap;

            } else {

                conn.disconnect();

                return null;

            }

        } catch (Throwable ex) {

            ex.printStackTrace();

            if (ex instanceof OutOfMemoryError)

                memoryCache.clear();

            return null;

        }

    }

private Bitmap decodeFile(File f) {

        try {

            // decode image size

            BitmapFactory.Options o = new BitmapFactory.Options();

            o.inJustDecodeBounds = true;

            FileInputStream stream1 = new FileInputStream(f);

            BitmapFactory.decodeStream(stream1, null, o);

            stream1.close();

            // Find the correct scale value. It should be the power of 2.

            final int REQUIRED_SIZE = 70;

            int width_tmp = o.outWidth, height_tmp = o.outHeight;

            int scale = 1;

            while (true) {

                if (width_tmp / 2 < REQUIRED_SIZE

                        || height_tmp / 2 < REQUIRED_SIZE)

                    break;

                width_tmp /= 2;

                height_tmp /= 2;

                scale *= 2;

            }

            // decode with inSampleSize

            BitmapFactory.Options o2 = new BitmapFactory.Options();

            o2.inSampleSize = scale;

            FileInputStream stream2 = new FileInputStream(f);

            Bitmap bitmap = BitmapFactory.decodeStream(stream2, null, o2);

            stream2.close();

            return bitmap;

        } catch (FileNotFoundException e) {

        } catch (IOException e) {

            e.printStackTrace();

        }

        return null;

    }

 

下載 Demo