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Ionic 4 HTTP CORS Issue

Ionic 4 is a major upgrade to previous version of Ionic. One of the primary differences between Ionic 4 and its previous incarnations is that Ionic 4 uses web components, which are custom HTML elements written using web standards (as opposed to using a slap-on framework such as Angular).
Ionic 4 also makes a fundamental change in how the created app is rendered (I use rendered as apps are essentially HTML which is rendered using the native WebView control of the device's UI framework) in a device. While earlier versions used to refer to the top level index.html using file:// URI scheme, Ionic 4 internally spins up an HTTP server on localhost (yes for each app) and then loads the index.html through a standard HTTP request such as http://localhost:port/index.html.
Problem I'm not sure what necessitated this change, but I reckon it probably had something to do with native API restrictions, which in turn was prompted by need for improved security. This, however, introduces a new (…

Notes of the day

A recent project requirement from a customer for a cross-platform solution prompted me to look into viable frameworks for this. Based on my knowledge of languages (C++, Python & Javascript), I narrowed the potential solutions to wxWidgets & Git Electron. Since I have been spending some time with Python over the last two years and given its ease of use, I through I'll look into wxPython, the Python projection of wxWidgets framework.

Here are my notes from this research today morning:
wxPython provides a genuine means to build cross platform GUI apps (installed through PyPi pip install wxpython).Python code can be compiled into distributable binaries using cx_Freeze, another cross-platform tool that can generate binaries for Windows, Mac & Linux. cx_Freeze can provide executable files as well as installable binaries such as MSI or DMG files.cx_Freeze source repo has sample code for various deployment scenarios. One of them is wxPython based application.Py2Exe is a popula…

Downloading & opening a file in an Ionic app

If you search the Internet for examples to achieve the above, you'll get a number of resources that suggest using the cordova-file-transfer plugin. However, with Ionic 3+ and its native API, you can do this directly using a mix of Angular and Ionic File API.

Essentially, you need to use Angular HttpClient to download a URL as a Blob using the responseType option and then save the resultant Blob to a file on the device using the File API. Finally, open the saved file using the Ionic native FileOpener API.

Here's the method in a provider that is used to download files from a website. Note that this.http is an instance of HttpClient.

/** * Download a file from the given url. * * Params: * url - the URL to download the file from * Returns: * A promise which upon resolution returns a dictionary * { * fileEntry: FileEntry, * type: The content-type string for the file * } */ download(url): Promise<{ fileEntry: FileEntry, type: s…

Cordova build errors

Had this unusual errors crop up when building a cordova app for android. This started appearing after I installed cordova-plugin-file-opener2.

ERROR: In <declare-styleable> FontFamilyFont, unable to find attribute android:fontVariationSettings ERROR: In <declare-styleable> FontFamilyFont, unable to find attribute android:ttcIndex
Going through platforms/android/project.properties file, I realized that there was something quite odd about it.

cordova.system.library.1=com.android.support:support-v13:26.+ cordova.system.library.2=me.leolin:ShortcutBadger:1.1.17@aar cordova.system.library.3=com.google.firebase:firebase-messaging:11.0.1 cordova.system.library.4=com.android.support:support-v4:27.1.0 cordova.system.library.5=com.android.support:support-v4:24.1.1+ cordova.system.library.6=com.android.support:support-v4:+
There were multiple versions of the same library being defined.

I removed the last three lines -- library.4, library.5 & library.6, ensuring that the the high…

Celery on Windows

Running celery on Windows, shows the following error when tasks are queued to be executed:
ValueError: not enough values to unpack (expected 3, got 0)
The way to fix this is to add --pool=solo to the celery daemon command line. This makes celery run as a solo process and without concurrency, which for development purposes shouldn't be a big deal.

So the entire daemon command would look something like this:
python -m celery -A config worker --pool=solo -l info
Taken from this Github thread.

Steps to Install Redis server

Few steps necessary to build and install Redis on a server. There are no pre-built packages available for you to apt-get install it. So you have to grab the source, compile and install the generated binaries. Fortunately it all goes pretty smooth. $ wget http://download.redis.io/releases/redis-4.0.2.tar.gz $ tar xzf redis-4.0.2.tar.gz $ cd redis-4.0.2 $ make $ make test # install compiled binaries to /ur/lib/bin $ sudo make install # setup redis-server as daemon $ cd utils $ sudo ./install_server.sh # setup redis-server to autostart $ sudo update-rc.d redis_6379 defaults
That ought to do it!

Volvo Door Mirror Mismatched Folding

One of the problems that I encountered with the S80 is that when I unlocked the car and pressed the button to unfold the door mirrors, they would be out of sync with each other. That is one would open and at the same time the other would close. You can open the closed mirror manually, but when you press the button to fold then mirrors, one would close and the the other would remain open.

After some research online, I figured out the problem -- the mirror's folded/open position is stored in memory and the car uses this position to instruct the mirror motors on what action to perform (fold/unfold) when you press the button to unfold the mirrors again. Now if you're in a hurry and happen to switch off the vehicle before the mirror folding operation could be completed, storing of the mirror position in memory cannot be completed accurately.

The solution to the problem turns out to be very simple.
Turn off the car.Locate the fuse box in the passenger compartment. Locate fuses for l…

How to Integrate Sphinx with a Django Project for Automatic Documentation Generation

A few points on integrating Sphinx with a Django redistributable project for generating documentation embedded in the source files.
Project directory structure should look like this:
django-redistributable/ demo/ demo/ settings.py urls.py wsgi.py templates/ manage.py docs/ conf.py index.rst Makefile make.bat redistributable/ models.py views.py templates/ static/ tests/ setup.py MANIFEST.in README.rst LICENSE requirements.txt Install sphinx and sphinx-autobuild using pip.Run sphinx-quickstart from the docs folder. Provide default answers for all prompts.Edit docs/conf.py such that the redistributable package and the demo project's apps are importable from the docs folder. At the top of the conf.py file:import os import sys import django sys.path.insert(0, os.path.dirname(os.path.dirname(__file__))) sys.path.append(os.path.join(os.path.dirname(os.path.dirname(__file__)), 'demo')) Setup sphinx such…

Volvo Engine Service Required Message

This is a message that my Volvo (S80 2004 2.0T) started showing yesterday. The message was accompanied with a yellow/orange warning light, (image on the right) in the car dash.

This freaked me out when it first appeared as I was worried that the car could shutdown anytime while on the move. But apparently the color of the light, yellow, is an indicator that the issue is not major and therefore such a shutdown is not an immediate possibility. On the other hand, if the color of the indicator is red, then it is indeed cause for concern and the best option is to stop the car and seek professional help immediately.

In the past whenever I had issues with my car, my first reaction is to reach out to my mechanic for help. But with the Volvo, what I have learned is that with the amount of electronics and computer control that is embedded into it, it's best to first to research online, narrow down the possible causes to a select few and then approach the mechanic appraising him of your res…

Volvo Service Reminder Message

This is a message that appears on my Volvo S80 after driving for a period of time. Interestingly, this message appears even though I have not driven the car for the recommended service interval - 7500 miles, or about 12000km.

Did some research and it turns out that this message is displayed as a function of hours the engine has been running, duration since last service and distance covered.  Essentially, this light will come on at 7,500 mile (12,000 km) intervals, after 750 hours of driving or after 12 months, whichever occurs first, to remind the driver that the service interval has been exceeded.

The light will stay on for 2 minutes after start until reset.

Here's how to reset this message without using a professional interface equipment:
Put the key in and turn it to ignition position IPress and hold in the reset button for the trip odometerTurn the key to ignition position II. Note! Turn the key to position II within 2 seconds.Hold the reset button for the trip meter pressed i…