Question

我希望如果我的应用程序第一次启动它应该从网上下载图像并将该图像存储在Device/Emulator，Device/Emulator中应该显示在ImageView中。我试过这样的方式：

ImageView myImgView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);     

    myImgView = (ImageView) findViewById(R.id.imageView1);      

    new MyAsnyc();
     Log.d(MY_TAGT, "AsyncTask Executed.....");

}
private class MyAsnyc extends AsyncTask<Void, Void,Void>{
    public File file ;
    InputStream is;
    private Bitmap bitmap;
    protected void doInBackground() throws IOException{

        File path = Environment.getExternalStoragePublicDirectory(
                Environment.DIRECTORY_PICTURES);
        file = new File(path, "DemoPicture.jpg");
        try{
            // Make sure the Pictures directory exists.
            path.mkdirs();

            URL url = new      URL(BASE_URL);
            /* Open a connection to that URL. */
            URLConnection ucon = url.openConnection();

            /*
             * Define InputStreams to read from the URLConnection.
             */
            is = ucon.getInputStream();

            OutputStream os = new FileOutputStream(file);
            byte[] data = new byte[is.available()];
            is.read(data);
            Log.i(MY_TAGT, "Picture is readable........");
            os.write(data);
            Log.i(MY_TAGT, "Picture is Saved........");
            is.close();
            os.close();

        }
        catch (IOException e) {
            Log.d("ImageManager", "Error: " + e);
        }
    }
    @Override
    protected Void doInBackground(Void... params) {
        // TODO Auto-generated method stub

        try {
            doInBackground();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return null;
    }
    protected void onPostExecute(){

        try{
            // Tell the media scanner about the new file so that it is
            // immediately available to the user.

            MediaScannerConnection.scanFile(null,
                    new String[] { file.toString() }, null,
                    new MediaScannerConnection.OnScanCompletedListener() {
                public void onScanCompleted(String path, Uri uri) {
                    Log.i("ExternalStorage", "Scanned " + path + ":");
                    Log.i("ExternalStorage", "-> uri=" + uri);
                }
            });
        }
        catch (Exception e) {
            // TODO: handle exception

        }

        /*Here I want to set this image in ImageView*/

        bitmap = BitmapFactory.decodeFile(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).toString()+"/DemoPicture.jpg");
        myImgView.setImageBitmap(bitmap);
    }
}

但是这样MyAsync类没有被执行，请告诉我们如何做到这一点。

EDIT这是我的日志

enter image description here

Answer 1

使用execute来调用它。

new MyAsnyc().execute();

Answer 2

使用

new MyAsnyc().execute();

而不是

new MyAsnyc();

因为用于执行AsyncTask的AsyncTask.execute(Params... params)方法

编辑：

使用While或for循环将文件中的数据写为：

OutputStream os = new FileOutputStream(file);
            byte[] data = new byte[is.available()];

            Log.i(MY_TAGT, "Picture is readable........");
            int count;
            while ( (count = is.read(data)) >= 0 ) {
              os.write(data,0,count)
             }

            Log.i(MY_TAGT, "Picture is Saved........");
            is.close();
            os.close();

Answer 3

您忘了执行AsyncTask：

(new MyAsnyc()).execute();

Answer 4

在行Log.d之前（MY_TAGT，＆＃34; AsyncTask执行.....＆＃34;）; 你只需构造新的AsyncTask对象，但你没有用execute（）方法调用它的执行。

编辑：第二个问题是它不是那么清楚WHICH图片实际上你想在那个ImageView中显示..导致bitmap = BitmapFactory.decodeFile（.. blahblahblah ..）在此之后可能会为null ..它似乎我给你文件夹名称，你想解码那个＆＃34;文件＆＃34; to bitmap ..制作一些关于这个解码和位图值的日志并向我们展示..

EDIT2：

File path = Environment.getExternalStoragePublicDirectory（Environment.DIRECTORY_PICTURES）; 文件文件=新文件（路径，＆＃34; DemoPicture.jpg＆＃34;）; bitmap = BitmapFactory.decodeFile（file）;

应该会好一点..

Answer 5

你必须试试这个：

public class DownloadImage {    
public static File getImage(String imageUrl, String fileName){
File file = null;
try {
    //set the download URL, a url that points to a file on the internet
    //this is the file to be downloaded         
    URL url = new URL(imageUrl);
    Log.d("INFORMATION..", "FILE FOUNDED....");
    //create the new connection
    HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

    //set up some things on the connection
    urlConnection.setRequestMethod("GET");
    urlConnection.setDoOutput(true);

    //and connect!
    urlConnection.connect();
    Log.d("INFORMATION..", "FILE CONECTED....");
    //set the path where we want to save the file
    //in this case, going to save it on the root directory of the
    //sd card.
    File SDCardRoot = Environment.getExternalStorageDirectory();
    //create a new file, specifying the path, and the filename
    //which we want to save the file as.
    file = new File(SDCardRoot, fileName);

    //this will be used to write the downloaded data into the file we created
    FileOutputStream fileOutput = new FileOutputStream(file);
    Log.d("INFORMATION..", "WRINTING TO FILE DOWNLOADED...." + file);
    //this will be used in reading the data from the internet
    InputStream inputStream = urlConnection.getInputStream();

    //this is the total size of the file
    int totalSize = urlConnection.getContentLength();
    //variable to store total downloaded bytes
    int downloadedSize = 0;

    //create a buffer...
    byte[] buffer = new byte[1024];
    int bufferLength = 0; //used to store a temporary size of the buffer

    //now, read through the input buffer and write the contents to the file
    while ( (bufferLength = inputStream.read(buffer)) > 0 ) {
        //add the data in the buffer to the file in the file output stream (the file on the sd card
        fileOutput.write(buffer, 0, bufferLength);
        //add up the size so we know how much is downloaded
        downloadedSize += bufferLength;
        Log.d("INFORMATION..", "FILE DOWNLOADED....");
        //this is where you would do something to report the prgress, like this maybe
        //updateProgress(downloadedSize, totalSize);

    }
    //close the output stream when done
    fileOutput.close();
    Log.d("INFORMATION..", "FILE DOWNLOADING COMPLETED....");
    //catch some possible errors...
} catch (MalformedURLException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}
return file;


 }
}

在DownloadImage.getImage(String imageUrl, String fileName)中拨打此MainActivity.java，如下所示：

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

ImageView imageView = (ImageView) findViewById(R.id.imageView1);

String url = "http://4.bp.blogspot.com/-8v_k_fOcfP8/UQIL4ufghBI/AAAAAAAAEDo/9ffRRTM9AnA/s1600/android-robog-alone.png"; 

String file = DownloadImage.getImage(url, "My Image.jpg").toString();

// Get file path on device and set it to imageView
Bitmap bitmap = BitmapFactory.decodeFile(file);
imageView.setImageBitmap(bitmap);
}
}

我认为这就是你要找的！希望这会对你有所帮助

AsyncTask不在onCreate（）中执行

5 个答案: