Friday, February 28, 2014

CSS inheritance sequence

    Starting today, I will also write about a few things CSS apart from Google Maps Javascript API and Jquery Mobile. I will cover some really interesting things in CSS and keep updating this blog as and when I learn something new and think its worth sharing with you all.

    Today we will look at a very common mostly known thing in CSS - the inheritance sequence of CSS. Most of you reading this post must be aware that there are 3 ways in which you can include CSS into your web application.

  • External Stylesheet
  • Internal Stylesheet
  • Inline Styles

External Style Sheet
    An external style sheet is ideal when you are writing a style that would be applied across multiple pages. The external style sheet gives the developer lot of control over the look and feel of the entire website or web application. The external style sheet is included using the the "link" tag which is included in the head section.

<link rel="stylesheet" href="styles/default.css" />

Internal Style Sheet
    An internal style sheet is used usually when a single document has unique style. The internal styles are written as part of the "style" tag which is again included in the "head" section.

<style>
    p{
        font-size: 20px;
        color: #a123bb;
    }
</style>

Inline Style
    An inline style loses many of the advantages of style sheets by mixing the content with the presentation. Inline styles should generally be avoided and be used when absolutely necessary and unavoidable!

<p style="font-size: 20px; color: #a123bb;"></p>

    As we know and/or have learned from experience, that these styles cascade into one, let's say a "virtual" style sheet which gets applied on the entire web site/application. This cascade follows the following sequence to override each other and create one final style sheet. Number #4 in the following list has the highest priority in the cascade.
  1. Browser default styles
  2. External style sheet
  3. Internal style sheet
  4. Inline styles
    So an inline styles has the highest priority, meaning that it will override a style defined inside the "head" tag, or in an external style sheet or the default browser styles. However, there are a few cases where this sequence of cascade can change!

Case #1: Usage of the !important keyword
    In case there is the "!important" keyword associated with an of the styles, then that style would get applied irrespective of whether it is part of the internal or the external style sheet.

Case #2: Javascript
    When styles are applied through javascript, these styles will override all styles included as part of the internal or external style sheet or even the inline styles.

Case #3: Sequence of inclusion of stylesheets
    If the link to the external style sheet is placed after the internal style sheet in the "head" tag, the external style sheet will override the internal stye sheet!

    Hope you have enjoyed this post and learned a few new things. Do let me know in case you want me to include a topic as part of the blog and I would be happy to write about it! Till then keep reading and keep sharing.

If this post has helped you, leave a comment or show your love by liking the Spatial Unlimited Facebook page. You could even consider buying me a coffe! Till next time; happy coding!

Thursday, February 20, 2014

Mobile web application - Remote debugging

    How many times have you come across issues on your web project which are specific to your Android devices, some particular version of it and on the Android stock browser or the installed webkit browser or the Chrome browser. Most of you must have been in this situation - "Things are working fine everywhere except on some Android version" - how many times do you see such issues/bugs raised by the QA team and you feel, if only I could debug on the mobile browser just like we do on the desktop browser using our developer tools.

    You can now heave a sigh of relief, you can now debug your mobile web application for any mobile specific issues if you have the issue on the Android Chrome browser. The chrome developer tools now allow the user to remotely debug a web application on Android devices. The experience of web content on mobile operates very differently than what users experience on the desktop. The Chrome DevTools allow you to inspect, debug and analyze the on-device experience with the full suite of tools you're used to, meaning you can use the tools in your desktop Chrome to debug a page on mobile Chrome.



    Debugging occurs over USB and as long as your mobile device is connected to your development machine, you can view and change HTML, scripts and styles until you get a bug-free page that behaves perfectly on all devices.


    To start debugging, you need to have:

  • An Android phone or tablet with Google Chrome for Android 32 or later installed from Google Play.
  • A USB cable to plug in your device. (Windows users will also need to install an appropriate USB device driver.)
  • Google Chrome 32 or later installed on the system you wish to use as your debugging host.

Step #1: Setting up your device

    In order to debug over USB, you need to setup your Android device for development.
    To enable USB debugging:
  • On Android 4.2 and newer, Developer options is hidden by default. To make it available, go to Settings > About phone and tap Build number seven times. Yup, just tap it 7 times, even if it seems crazy. Then, return to the previous screen to find Developer options.
  • On Android 4.0 and 4.1, it's in Settings > Developer options.
  • On most devices running Android 3.2 or older, you can find the option under Settings > Applications > Development


Step #2: Connecting directly over USB

    DevTools now supports native USB debugging of connected devices. You no longer need to configure ADB or the ADB plugin to see all instances of Chrome and the Chrome-powered WebView. on devices connected to your system. This functionality works on all OS's: Windows, Mac, Linux and Chrome OS. Just visit "about:inspect" and verify Discover USB Devices is checked. This direct USB connection between Chrome and the device may interrupt an `adb` connection that you may be trying to establish. If you need to use the `adb` binary for other reasons, uncheck the "Discover USB Devices" checkbox, unplug the device, and plug it back in, before establishing your connection via `adb devices`.


    If you encounter problems with the above technique, or are using an older version of Chrome, you can try the legacy workflow for connectivity which uses the adb binary from the Android SDK.
  • Connect your mobile device to the host using a USB cable.
  • Ensure your device is listed as available, by issuing the adb devices command. If not, please check that you have USB debugging enabled on your device.
  • On the mobile device, launch Chrome. Open Settings > Advanced > DevTools and check the Enable USB Web debugging option.
  • Issue the following command in the terminal or console on your host machine to enable port forwarding:
adb forward tcp:9222 localabstract:chrome_devtools_remote

  • If you get a "device not found" error, run the adb kill-server command to resolve.
  • Now open desktop Chrome and navigate to localhost:9222.
  • You will be presented with the set of thumbnails for pages currently open in tabs on your mobile Chrome. Choose the page you would like to debug.


Step #3: Connect your device
  • Connect your mobile device to the development machine using a USB cable.
  • When connecting your device to your development machine, you may see an alert on the device requesting permission for USB debugging from this computer. To avoid seeing this alert each time you debug, check Always allow from this computer and click OK.


    Now, to see all connected devices, go to the Chrome menu > Tools > Inspect Devices:


  • You can have multiple devices simultaneously connected as well as multiple versions of Chrome open on each device.
  • You will be presented with the set of thumbnails for pages currently open in tabs on your mobile Chrome. Choose the page you would like to debug. Find the tab you're interested in and click the inspect link to open DevTools on it. You may also reload the page, bring it to the front, or close it. Lastly, you can open new links on the device through a text input field.
Step #4: Debug your Application
    You can now start debugging and profiling mobile content in the DevTools on your desktop.



    For example, inspect an element in the page you have selected and you will notice the element highlight in Chrome mobile on your device in real time.


    Similarly, editing scripts or executing commands from the Dev Tools console will also apply to the page being inspected on your device, as seen below.


    Hope this article helps you resolve the device specific issues better and hope this has saved you some time and loads of frustration. Till next time, keep reading, keep developing, keep deploying! =)

If this post has helped you, leave a comment or show your love by liking the Spatial Unlimited Facebook page. You could even consider buying me a coffe! Till next time; happy coding!