Tutorial by Examples: co

componentWillReceiveProps(nextProps) This is the first function called on properties changes. When component's properties change, React will call this function with the new properties. You can access to the old props with this.props and to the new props with nextProps. With these variables, you c...

componentWillUnmount() This method is called before a component is unmounted from the DOM. It is a good place to perform cleaning operations like: Removing event listeners. Clearing timers. Stopping sockets. Cleaning up redux states. componentWillUnmount(){ ... } An example of remo...

With automatic reference counting (ARC), the compiler inserts retain, release, and autorelease statements where they are needed, so you don't have to write them yourself. It also writes dealloc methods for you. The sample program from Manual Memory Management looks like this with ARC: @interface M...

The isEqual: method is the only reliable way to determine whether two images contain the same image data. The image objects you create may be different from each other, even when you initialize them with the same cached image data. The only way to determine their equality is to use the isEqual...

Haskell has list comprehensions, which are a lot like set comprehensions in math and similar implementations in imperative languages such as Python and JavaScript. At their most basic, list comprehensions take the following form. [ x | x <- someList ] For example [ x | x <- [1..4] ] -...

Using the Story Board: Select the tab bar item from the corresponding view controller and go to the attributes inspector If you want a built-in icon and title, set the 'System Item' to the corresponding value. For a custom icon, add the required images to the assets folder and set the 'System It...

If you need an ActiveRecord method to raise an exception instead of a false value in case of failure, you can add ! to them. This is very important. As some exceptions/failures are hard to catch if you don't use ! on them. I recommended doing this in your development cycle to write all your ActiveRe...

Sometimes you may want to apply styling to a column or group of columns. Or for semantic purposes, you may want to group columns together. To do this, use <colgroup> and <col> elements. The optional <colgroup> tag allows you to group columns together. <colgroup> elements ...

See this Q&A question if you don't know what race conditions are. The following code may be subject to race conditions : article = Article.objects.get(pk=69) article.views_count += 1 article.save() If views_count is equal to 1337, this will result in such query: UPDATE app_article SET vi...

Orders Table CustomerIdProductIdQuantityPrice12510013220014150021450356700 To check for customers who have ordered both - ProductID 2 and 3, HAVING can be used select customerId from orders where productID in (2,3) group by customerId having count(distinct productID) = 2 Return value:...

Go to File -> Settings -> Editor -> Colors & Fonts -> Android Logcat Change the colors as you need: Choose the appropriate color:

Some basic types and classes in Java are fundamentally mutable. For example, all array types are mutable, and so are classes like java.util.Data. This can be awkward in situations where an immutable type is mandated. One way to deal with this is to create an immutable wrapper for the mutable type...

Func also supports Covariant & Contravariant // Simple hierarchy of classes. public class Person { } public class Employee : Person { } class Program { static Employee FindByTitle(String title) { // This is a stub for a method that returns // an employee that h...

The double-colon syntax of names in the use statement looks similar to names used elsewhere in the code, but meaning of these paths is different. Names in the use statement by default are interpreted as absolute, starting at the crate root. Names elsewhere in the code are relative to the current mo...

Array.join(separator) can be used to output an array as a string, with a configurable separator. Default (separator = ","): ["a", "b", "c"].join() === "a,b,c" With a string separator: [1, 2, 3, 4].join(" + ") === "1 + 2 + 3 + 4&q...

To convert decimal number to binary format use base 2 Int32 Number = 15; Console.WriteLine(Convert.ToString(Number, 2)); //OUTPUT : 1111 To convert decimal number to octal format use base 8 int Number = 15; Console.WriteLine(Convert.ToString(Number, 8)); //OUTPUT : 17 To conv...

Highchart by default puts a credits label in the lower right corner of the chart. This can be removed using credits option in your chart settings. credits: { enabled: false } Or credits: false will remove the highcharts.com logo.

GetLastError returns a numerical error code. To obtain a descriptive error message (e.g., to display to a user), you can call FormatMessage: // This functions fills a caller-defined character buffer (pBuffer) // of max length (cchBufferLength) with the human-readable error message // for a Win32 ...

Object oriented style Connect to Server $conn = new mysqli("localhost","my_user","my_password"); Set the default database: $conn->select_db("my_db"); Connect to Database $conn = new mysqli("localhost","my_user","my_password&q...

When we are finished querying the database, it is recommended to close the connection to free up resources. Object oriented style $conn->close(); Procedural style mysqli_close($conn); Note: The connection to the server will be closed as soon as the execution of the script ends, unless it...