Question

I want to download an image from server, save it on the SD card, and show it.
I wrote that code, but it doesn’t work – there are no bugs, but I see only a black screen instead of the image.

public class Main extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    MyTask mt = new MyTask();
    mt.execute();

    Intent intent = new Intent();  
    intent.setAction(android.content.Intent.ACTION_VIEW);  
    File file = new File("/sdcard/askeroid/logos/1_mobile.png");  
    intent.setDataAndType(Uri.fromFile(file), "image/*");  
    startActivity(intent); 
}  

}
class MyTask extends AsyncTask {

@Override
protected Void doInBackground(Void... params) {
    try{
        URL url = new URL("http://ed.sadko.mobi/logo/logo_1mobile.png");
        URLConnection connection = url.openConnection();
        connection.connect();

        InputStream input = new BufferedInputStream(url.openStream());
        OutputStream output = new FileOutputStream("/sdcard/askeroid/logos/1_mobile.png");

        output.flush();
        output.close();
        input.close();

    } catch(Exception e){e.printStackTrace();}
  return null;
}

}

Answer 1

You don’t wait for the end of the download before moving to next activity.

I suggest you use AsyncTask – download the image using in doInBackground and start next activity in onPostExecute.

Something like:

AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {
    @Override protected Long doInBackground(Void ... urls) {
        // download the image
    }

    @Override protected void onPostExecute(Void result) {
        // start new activity...
    }
};
task.execute();

Also, please note that the path to the SD card may vary between different devices. Take a look here to see how to access it properly.