Tutorial by Examples: re

How to add Swipe-to-Refresh To your app

Make sure the following dependency is added to your app's build.gradle file under dependencies: compile 'com.android.support:support-core-ui:24.2.0' Then add the SwipeRefreshLayout in your layout: <android.support.v4.widget.SwipeRefreshLayout android:id="@+id/swipe_refresh_layo...

Android • Swipe to Refresh

if()...else Ladder Chaining two or more if () ... else statements

While the if ()... else statement allows to define only one (default) behaviour which occurs when the condition within the if () is not met, chaining two or more if () ... else statements allow to define a couple more behaviours before going to the last else branch acting as a "default", i...

C Language • Selection Statements

Weak References

In .NET, the GC allocates objects when there are no references left to them. Therefore, while an object can still be reached from code (there is a strong reference to it), the GC will not allocate this object. This can become a problem if there are a lot of large objects. A weak reference is a ref...

C# Language • Garbage Collector in .Net

Global Interpreter Lock (GIL) and blocking threads

Plenty has been written about Python's GIL. It can sometimes cause confusion when dealing with multi-threaded (not to be confused with multiprocess) applications. Here's an example: import math from threading import Thread def calc_fact(num): math.factorial(num) num = 600000 t = Threa...

Python Language • Common Pitfalls

Difference between allocation and initialization

In most object oriented languages, allocating memory for an object and initializing it is an atomic operation: // Both allocates memory and calls the constructor MyClass object = new MyClass(); In Objective-C, these are separate operations. The class methods alloc (and its historic sibling allo...

Objective-C Language • Classes and Objects

Reading and writing data frames

Data frames are R's tabular data structure. They can be written to or read from in a variety of ways. This example illustrates a couple common situations. See the links at the end for other resources. Writing Before making the example data below, make sure you're in a folder you want to write to....

R Language • Input and output

Type erasing type erasure with std::any

This example uses C++14 and boost::any. In C++17 you can swap in std::any instead. The syntax we end up with is: const auto print = make_any_method<void(std::ostream&)>([](auto&& p, std::ostream& t){ t << p << "\n"; }); super_any<decltype(print...

C++ • Type Erasure

Drawing two rectangles on a

<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8" /> <title>Draw two rectangles on the canvas</title> <style> canvas{ border:1px solid gray; } </style> <script async...

HTML • Canvas

Remote module RMI

The remote module allows simple RMI (remote method invocation) of main process objects from renderer process. First create the main process in index.js const {app, BrowserWindow} = require('electron') let win = null app.on('ready', () => { win = new BrowserWindow() win.loadURL(`file://...

electron • Main and renderer process.

Default compositing: New shapes are drawn over Existing shapes

context.globalCompositeOperation = "source-over" "source-over" compositing [default], places all new drawings over any existing drawings. context.globalCompositeOperation='source-over'; // the default context.drawImage(background,0,0); context.drawImage(parachuter,0,0); ...

html5-canvas • Compositing

Using Resolvers and Guards

We're using a toplevel guard in our route config to catch the current user on first page load, and a resolver to store the value of the currentUser, which is our authenticated user from the backend. A simplified version of our implementation looks as follows: Here is our top level route: export c...

Angular 2 • Routing (3.0.0+)

Create a Bluetooth LE Advertisement

This example shows how to advertise a custom payload from a Windows 10 device in the foreground. The payload uses a made up company (identified as 0xFFFE) and advertises the string Hello World in the advertisement. BluetoothLEAdvertisementPublisher publisher = new BluetoothLEAdvertisementPublisher(...

bluetooth • Get Started With Bluetooth LE on Windows

Count the number of foreign relations

class Category(models.Model): name = models.CharField(max_length=20) class Product(models.Model): name = models.CharField(max_length=64) category = models.ForeignKey(Category, on_delete=models.PROTECT) To get the number products for each category: >>> categories = Ca...

Django • Model Aggregations

A column is computed from an expression

A computed column is computed from an expression that can use other columns in the same table. The expression can be a noncomputed column name, constant, function, and any combination of these connected by one or more operators. Create table with a computed column Create table NetProfit ( Sa...

Microsoft SQL Server • Computed Columns

Run once before testing condition

Sometimes, one wants to run some initialization code once before testing a condition. In certain other languages, this kind of loop has special do-while syntax. However, this syntax can be replaced with a regular while loop and break statement, so Julia does not have specialized do-while syntax. Ins...

Julia Language • while Loops

Breadth-first search

0.5.0 (Although this example is written using syntax introduced in version v0.5, it can work with few modifications on older versions also.) This implementation of breadth-first search (BFS) on a graph represented with adjacency lists uses while loops and the return statement. The task we will sol...

Julia Language • while Loops

Pitfall - Extending 'java.lang.Thread'

The javadoc for the Thread class shows two ways to define and use a thread: Using a custom thread class: class PrimeThread extends Thread { long minPrime; PrimeThread(long minPrime) { this.minPrime = minPrime; } public void run() { // compute primes l...

Java Language • Java Pitfalls - Threads and Concurrency

Pitfall - Too many threads makes an application slower.

A lot of people who are new to multi-threading think that using threads automatically make an application go faster. In fact, it is a lot more complicated than that. But one thing that we can state with certainty is that for any computer there is a limit on the number of threads that can be run at ...

Java Language • Java Pitfalls - Threads and Concurrency

Using return

Returning a value One commonly used case: returning from main() #include <stdlib.h> /* for EXIT_xxx macros */ int main(int argc, char ** argv) { if (2 < argc) { return EXIT_FAILURE; /* The code expects one argument: leave immediately skipping t...

C Language • Jump Statements

Using break and continue

Immediately continue reading on invalid input or break on user request or end-of-file: #include <stdlib.h> /* for EXIT_xxx macros */ #include <stdio.h> /* for printf() and getchar() */ #include <ctype.h> /* for isdigit() */ void flush_input_stream(FILE * fp); int main(v...

C Language • Jump Statements