Wednesday, 21 June 2017

Alchemy app released (in beta)

I've finally published the beta version of Alchemy on the play store. It's still in beta, but it seems to be working well. Give it a shot if you're looking for a different way to donate to charity!

Tuesday, 20 June 2017

Memory leak with android linearlayout and Picasso

I recently ran into an issue using Picasso with Android's linearlayout. I was using Picasso to load images from a url into a linearlayout, handling errors with Picasso's build object as follows:

Picasso.Builder builder = new Picasso.Builder(this.mContext);
builder.listener(new Picasso.Listener()
{
    @Override
    public void onImageLoadFailed(Picasso picasso, Uri uri, Exception exception)
    {
      picasso.load(mThumbIds[0]).into(imageView); // on failure just load the default image
    }
});
Picasso picasso= builder.build();


I was recycling the images correctly with convertView (using a viewholder class), but I couldn't track down the source of a memory leak which occured every time a new image was loaded - eventually causing the app to crash. The leak however when away when I stopped using Picasso's builder, instead just using a simple try catch setup.

try{
    Picasso.with(mContext).load(logo_url).placeholder(R.drawable.alchemy).into(holder.imageView);
}
catch (Throwable e){
     Picasso.with(mContext).load(R.drawable.alchemy).into(holder.imageView);
}

Sunday, 28 May 2017

Installing OpenCV3 for Python 3 on Windows

I need to use python for face recognition as part of the server for a charity app I'm working on. The app is supposed to show charity logos, but in the case of smaller charities, sometimes the google custom search I use to search for the logos returns instead a picture with a person in it. I need to identify cases where this happens and use a placeholder image instead.

My first attempt to install opencv was through pip from anaconda:

pip install opencv-python

However this gave me the following error when I tried to import cv2:

ImportError: DLL load failed: The specified module could not be found.

I uninstalled the anaconda version and found a 64 bit wheel of opencv for python 3.6 at http://www.lfd.uci.edu/~gohlke/pythonlibs/#opencv. Downloading this and installing it with pip worked perfectly. I don't know why the original error occured, but it looks like python 3 support might not be great with opencv at the moment.

Thursday, 18 May 2017

Using Python 3 to extract files from an encrypted archive with a password

Recently I needed to use python to extract the contents of a password-protected zip archive and I came across a few issues I thought would be good to document.

Python has a build in zipfile library that is really good at handling zip files, but unfortunately has a few limitations when it comes to encrypted zip files. This is how Python3 can be used to extract a file from an encrypted zip archive:


The first issue that I came across was some unclear documentation for the "open" method of zipfile in Python 3. The open method uses the "pwd" argument to pass the password for the file, but in Python 3 you need to convert this to bytes before calling open. Unfortunately, the library only seems to support CRC-32 based encryption  - meaning that the default linux zip encryption will work, but AES will not. I was also unable to get this to work with 7zip and WinZip.

Saturday, 22 April 2017

New website design

It had been a while since I updated my website so I found a new template from http://themes.3rdwavemedia.com and redesigned the whole site. I particularly like the github and blog integration with the new theme - hopefully that will encourage me to write more here too, especially as I'm working on the new Alchemy app.

Sending an SMS via Intent in Android

Alchemy allows users to donate to their chose charities via text message, which it used to do automatically using Android's SmsManager ...