Tutorial by Examples: an

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

Adding dependencies from another project

project('projectA') { task A(dependsOn: ':projectB:B') << { println 'Hello from A' } } project('projectB') { task B << { println 'Hello from B' } } To refer to a task in another project, you prefix the name of the task with the path of the pr...

gradle • Task dependencies

Installation and Setup

To install React Router, just run the npm command npm install --save react-router And you're done. This is literally all you have to do to install react router. Please Note : react-router is dependent on react, So make sure you install react as well. To set up: using an ES6 transpiler, like bab...

React Router • Getting started with React Router

Detect errors when writing a value on Android

There are many reasons a write operation may fail. A frequent one is because your security rules reject the operation, for example because you're not authenticated (by default a database can only be accessed by an authenticated user). You can see these security rule violations in the logcat output....

firebase • How do I listen for errors when accessing the database?

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+)

Atomic transactions

Problem By default, Django immediately commits changes to the database. When exceptions occur during a series of commits, this can leave your database in an unwanted state: def create_category(name, products): category = Category.objects.create(name=name) product_api.add_products_to_cate...

Django • Database transactions

Finding all branches with no merged changes

Sometimes you might have branches lying around that have already had their changes merged into master. This finds all branches that are not master that have no unique commits as compared to master. This is very useful for finding branches that were not deleted after the PR was merged into master. ...

Git • Merging

Showing additional information when an exception occurs

It's important to handle exceptions in your service. When developing the service, you can set the WCF to provide more detailed information, adding this tag to configuration file, usually Web.config: <serviceDebug includeExceptionDetailInFaults="true"/> This tag must be placed w...

wcf • Handling exceptions

Getters and Setters

void main() { var cat = new Cat(); print("Is cat hungry? ${cat.isHungry}"); // Is cat hungry? true print("Is cat cuddly? ${cat.isCuddly}"); // Is cat cuddly? false print("Feed cat."); cat.isHungry = false; print("Is cat ...

dart • Getting started with dart

implement View.OnLayoutChangeListener in Nativescript

let playerLayoutChangeListener = new android.view.View.OnLayoutChangeListener( { onLayoutChange : function ( v:View, left:number, top:number, right:number, bottom:number, oldLeft:number, oldTop:number, oldRight:number, oldBottom:number):any { if (left != oldLeft || top != oldTop ...

nativescript • implement Interface

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

Standard Operators

Julia supports a very large set of comparison operators. These include All of the following unicode sequences: > < >= ≥ <= ≤ == === ≡ != ≠ !== ≢ ∈ ∉ ∋ ∌ ⊆ ⊈ ⊂ ⊄ ⊊ ∝ ∊ ∍ ∥ ∦ ∷ ∺ ∻ ∽ ∾ ≁ ≃ ≄ ≅ ≆ ≇ ≈ ≉ ≊ ≋ ≌ ≍ ≎ ≐ ≑ ≒ ≓ ≔ ≕ ≖ ≗ ≘ ≙ ≚ ≛ ≜ ≝ ≞ ≟ ≣ ≦ ≧ ≨ ≩ ≪ ≫ ≬ ≭ ≮ ≯ ≰ ≱ ≲ ≳ ≴ ≵ ≶ ≷ ≸ ≹ ≺ ...

Julia Language • Comparisons

Error cleanup

In languages such as C, the @goto statement is often used to ensure a function cleans up necessary resources, even in the event of an error. This is less important in Julia, because exceptions and try-finally blocks are often used instead. However, it is possible for Julia code to interface with C ...

Julia Language • @goto and @label

Working with pathnames and filenames

% set mypath /home/tcluser/sources/tcl/myproject/test.tcl /home/tcluser/sources/tcl/myproject/test.tcl % set dir [file dirname $mypath] /home/tcluser/sources/tcl/myproject % set filename [file tail $mypath] test.tcl % set basefilename [file rootname $filename] test % set extension [file exte...

tcl • Pathnames and filenames

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 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

Change selected tab programatically from child Page

You can take a look at the full code in this working Plunker. In this example I use a shared service to handle the communication between the pages inside the tab (child pages) and the tab container (the component that holds the tabs). Even though you probably could do it with Events I like the shar...

ionic2 • Using Tabs

Pitfall - Declaring classes with the same names as standard classes

Sometimes, programmers who are new to Java make the mistake of defining a class with a name that is the same as a widely used class. For example: package com.example; /** * My string utilities */ public class String { .... } Then they wonder why they get unexpected errors. For ex...

Java Language • Java Pitfalls - Language syntax

Pulling changes to a local repository

Simple pull When you are working on a remote repository (say, GitHub) with someone else, you will at some point want to share your changes with them. Once they have pushed their changes to a remote repository, you can retrieve those changes by pulling from this repository. git pull Will do it, ...

Git • Pulling