Programming

All languages have certain semantics for dealing with error cases. C deals with them by setting error codes. Java deals with them by throwing exceptions. JavaScript deals with them by throwing exceptions as well but unlike Java, it does have any concept of checked Exceptions. The JS interpreter just stops. And this has some interesting implications in hybrid scenarios like a Webview based app. Consider a simple Android app where most of the code is in JavaScript but is making a request to Java layer. ...

The core idea behind resumable upload is straightforward if you are uploading a big file, then you are going to encounter users in the network conditions where they cannot upload the file in a single network session. The client-side code, to avoid restarting the file upload from the beginning, must figure out what portion of the file was uploaded and “resume” the upload of the rest. How to do resumable upload Before starting the upload, send a unique ID generated from the file contents to the server like MD-5 or SHA-256. The server decides and declares what the format of that unique ID is. Next, the server responds with an offset which indicates how many bytes server already has. The client uploads rest of the bytes with a Content-Range header. ...

Some video streaming websites like YouTube provides an option for speeding up/slowing down videos; some don’t. The trick is simple, find out the Video object via Js 1 document.querySelector("video") and then set its playbackRate property to the desired value ...

This is a long post. It covers several decisions like API version, distribution beyond play store, UI & network performance, and minimizing RAM, disk, and battery usage.

Android development requires tons of disconnected approaches for development and testing. Consider some scenarios To test runtime permission - Go to Settings -> Applications -> Application info of the app you are looking for and disable that permission. To test a fresh install - adb shell pm clear-data com.example To test your app under the battery-saver mode - turn on the battery saver mode by expanding the notification bar To stop the execution of an app - kill it via activity manager, adb shell am kill com.example To test your app under doze mode - first, make the device believe that it is unplugged via “adb shell dumpsys battery unplug”, then, make it think that it is discharging via “adb shell dumpsys battery set status 3”, and then enable doze mode via “adb shell dumpsys deviceidle force-idle”. And don’t forget to execute a set of unrelated complementary commands once you are done to bring the device back to its normal state. To see the overdraw of the app - Go to the developer options and enable/disable it there. Over time, this became a significant mental burden that I first wrote some of these flows in a text file and then converted them to automated shell scripts. But when even that felt insufficient, I created a tool for myself called adb-enhanced. ...

It is impressive to see the amount of similarity which exists in Swift, Kotlin and Go, the three new languages for iOS, Android, and server-development respectively. Consider a simple, Hello World program. Swift Swift 1 2 3 4 5 func printHello() { // Type automatically inferred to string let name = "Ashish" // let declares a read-only variable print("Hello world from \(name)!") } Kotlin ...

Let’s say you are developing an Android app com.example.android and want to access its database file named “content” from the test device/emulator. To access this file, located in app’s database directory, on both rooted and unrooted device would be Bash 1 2 3 4 5 $ APP_NAME=com.example.android $ adb shell run-as $APP_NAME cp databases/content.db /sdcard/content.db && $ adb pull /sdcard/content.db content.db && $ adb shell rm /sdcard/content.db ... This seems to work but is incorrect. An SQLite database can have write-ahead logging (-wal) file, a journal (-journal), and shared memory (-shm) file. Anytime, you copy just the .db file; you might get an old copy of the database, the right way to copy is to copy all the four files, so that, the SQLite on the laptop displays the combined result. ...

Occasionally, my mac applications end up in a corrupt state where they won’t open. I recently encountered this with Deluge. The first step to diagnose is to open Terminal and open them in the terminal via Sh 1 2 $ open -a deluge # This name is same as the name of the app (minus the ".app" portion). LSOpenURLsWithRole() failed for the application /usr/local/Caskroom/deluge/1.3.12/Deluge.app with error -10810. Now, the error is more diagnosable but still cryptic. Deluge.app above is a directory and we can navigate to the binary located at Deluge.app/Contents/MacOS/Deluge and execute the actual binary to see a more actionable error ...

Java has fewer quirks compared to C++, but sometimes I do come across surprises. A code like following will fail to compile since you are trying to initialize a variable with an uninitialized variable. Java 1 2 3 4 5 6 7 8 9 public class Sample { private final String mField1; private final String mField2 = mField1 + " two"; private Sample(String field1) { mField1 = field1; } } But if instead of directly referencing mField1, you reference indirectly via a getter method code will compile, and mField2 will get “null” value for mField1. ...

Almost everyone developing an Android app has seen something like this in their device logs. Bash 1 I/Choreographer(1200): Skipped 60 frames! The application may be doing too much work on its main thread. On most devices, the Android platform tries to render a new frame every 16 milliseconds (60 fps). The rendering requires that whatever work is happening on the UI thread should finish in that timeframe (well, actually in less than that). Any unit of work (== Runnable) scheduled on the UI thread has to fit in that. When the work takes longer, then frames are skipped. One skipped frame is 16 ms of the hung screen. The UI looks janky and unresponsive and if the user interacts with the screen and the application does not respond in time ( 5 seconds) then Application Not Responding (ANR) shows up. ...