从服务器下载图片并保存到SD卡，不使用BitmapFactory。

Question

从服务器下载图片并保存到SD卡，不使用BitmapFactory。

5

我正在创建一个应用程序，用于从服务器下载图像并在ListView中显示。我遇到的问题是内存泄漏，导致我的应用程序崩溃。我在 Android 博客中搜索了一些文章，例如此链接，它提供了一个很好的想法，但仍然不能够在多个线程中使用。一些 Android 设备可以处理它，但有些设备只能在单个线程中处理，有时根本无法工作。

我的应用程序有许多活动，每个活动都有一个需要尽可能快速地显示图像的 ListView。通过 Google IO 2012，他们使用缓冲区将原始图像保存到 SD 卡中，并解决了内存泄漏的问题，但由于需要下载的图像太大，加载速度太慢。

我的问题是：有没有办法将图像缩放并将其写入SD卡？我找到了一些可能的解决方案，如在 inputstream 对象中使用 Skip byte，我还能够找到需要下载的图像的宽度、高度和每像素位数。

以下代码在 Google IO 2012 中使用，可以很好地支持多线程，在我的情况下，我有四个线程在后台运行。

private void downloadAndWriteFile(final String url, final File file) throws OutOfMemoryError {
    BufferedOutputStream out = null;

    try {
        HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
        conn.setDoInput(true);
        conn.connect();

        final InputStream in = new BufferedInputStream(conn.getInputStream(), IO_BUFFER_SIZE_BYTES);    // buffer size 1KB
        out = new BufferedOutputStream(new FileOutputStream(file), IO_BUFFER_SIZE_BYTES);

        int b;
        while ((b = in.read()) != -1) {
            out.write(b);
        }
        out.close();
        conn.disconnect();
    }
    catch (Exception e) {
        Log.e(TAG, "!!downloadAndWriteFile " + e.getMessage());
        file.delete();
    }
}

- vsatkh

3个回答

0

你可以使用这个。

private void downloadImagesToSdCard(String downloadUrl,String imageName) {
try {
    URL url = new URL(downloadUrl); //you can write here any link

    File myDir =  new File("/sdcard"+"/"+Constants.imageFolder);
    //Something like ("/sdcard/file.mp3")


    if (!myDir.exists()) {
        myDir.mkdir();
        Log.v("", "inside mkdir");

    }

    Random generator = new Random();
    int n = 10000;
    n = generator.nextInt(n);
    String fname = imageName;
    File file = new File (myDir, fname);
    if (file.exists ()) file.delete (); 

         /* Open a connection to that URL. */
        URLConnection ucon = url.openConnection();
        InputStream inputStream = null;
       HttpURLConnection httpConn = (HttpURLConnection)ucon;
      httpConn.setRequestMethod("GET");
      httpConn.connect();

      if (httpConn.getResponseCode() == HttpURLConnection.HTTP_OK) {
       inputStream = httpConn.getInputStream();
      }

        /*
         * Define InputStreams to read from the URLConnection.
         */
       // InputStream is = ucon.getInputStream();
        /*
         * Read bytes to the Buffer until there is nothing more to read(-1).
         */

        FileOutputStream fos = new FileOutputStream(file);
        int size = 1024*1024;
        byte[] buf = new byte[size];
        int byteRead;
        while (((byteRead = inputStream.read(buf)) != -1)) {
            fos.write(buf, 0, byteRead);
            bytesDownloaded += byteRead;
        }
        /* Convert the Bytes read to a String. */

        fos.close();

} catch(IOException io) {
    networkException = true;
    continueRestore = false;
} catch(Exception e) {   
    continueRestore = false;
    e.printStackTrace();
}

}

- Chetan Urmaliya

0

这段代码可以在不使用位图工厂的情况下下载图片，但无法在模拟器中运行，请使用任何安卓手机。

package com.example.filedownload;


import org.apache.http.util.ByteArrayBuffer;

import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.content.*;
import android.app.*;
import android.net.*;
import android.app.DownloadManager.Request;
import android.os.Environment;
public class MainActivity extends Activity {
    public  long reference;
    BroadcastReceiver receiver;
    @Override
        protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        Button button=(Button)findViewById(R.id.button1);
                button.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {


                                String file = "http://tmacfitness.com/wp-content/uploads/2013/04/Beauty-of-nature-random-4884759-1280-800.jpg";
                                String serviceString = Context.DOWNLOAD_SERVICE; 
                                DownloadManager downloadManager;
                                downloadManager = (DownloadManager)getSystemService(serviceString);
                                Uri uri = Uri.parse(file);
                                DownloadManager.Request request ;
                                request =  new Request(uri);
                                request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS,  "accel.jpg");   
                                reference = downloadManager.enqueue(request);



                }

        });

        IntentFilter filter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE);
        receiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
        long ref = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
        if (reference == ref) {
        setContentView(R.layout.finalscreen);
        unregister();
        }
        }
        };
        registerReceiver(receiver, filter); 
    }
       public void unregister(){
           unregisterReceiver(receiver);

    }
}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <TableLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true" >

        <TableRow
            android:id="@+id/tableRow1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >
        </TableRow>

        <TableRow
            android:id="@+id/tableRow2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <CheckedTextView
                android:id="@+id/checkedTextView1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Accel" />

        </TableRow>

        <TableRow
            android:id="@+id/tableRow3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <Button
                android:id="@+id/button1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Button" />

        </TableRow>

        <TableRow
            android:id="@+id/tableRow4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >
        </TableRow>
    </TableLayout>

</RelativeLayout>

finalscreen.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="270dp"
        android:layout_height="wrap_content"
        android:layout_weight="2.12"
        android:text="DOWNLOAD COMPLETED" />

</LinearLayout>

- learner

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Bobs · Accepted Answer

1) 在设置图像之前，请使用以下代码释放与此位图关联的本机对象，并清除对像素数据的引用。如果没有其他引用，它只是允许垃圾回收。

BitmapDrawable drawable = (BitmapDrawable) myImage.getDrawable();
Bitmap bitmap = drawable.getBitmap();
if (bitmap != null)
{
    bitmap.recycle();
}

2) 使用此方法来减少内存中位图的大小：

/**
 * decodes image and scales it to reduce memory consumption
 * 
 * @param file
 * @param requiredSize
 * @return
 */
public static Bitmap decodeFile(File file, int requiredSize) {
    try {

        // Decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(new FileInputStream(file), null, o);

        // The new size we want to scale to

        // Find the correct scale value. It should be the power of 2.
        int width_tmp = o.outWidth, height_tmp = o.outHeight;
        int scale = 1;
        while (true) {
            if (width_tmp / 2 < requiredSize
                    || height_tmp / 2 < requiredSize)
                break;
            width_tmp /= 2;
            height_tmp /= 2;
            scale *= 2;
        }

        // Decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;

        Bitmap bmp = BitmapFactory.decodeStream(new FileInputStream(file),
                null, o2);

        return bmp;

    } catch (FileNotFoundException e) {
    } finally {
        System.gc();
    }
    return null;
}