Tutorial by Examples: v

DBContract.java //Define the tables and columns of your local database public final class DBContract { /*Content Authority its a name for the content provider, is convenient to use the package app name to be unique on the device */ public static final String CONTENT_AUTHORITY =...

In C#, types can define custom Conversion Operators, which allow values to be converted to and from other types using either explicit or implicit casts. For example, consider a class that is meant to represent a JavaScript expression: public class JsExpression { private readonly string expres...

Matplotlib supports both object-oriented and imperative syntax for plotting. The imperative syntax is intentionally designed to be very close to Matlab syntax. The imperative syntax (sometimes called 'state-machine' syntax) issues a string of commands all of which act on the most recent figure or a...

First, ensure you have imported sessions from flask from flask import session To use session, a Flask application needs a defined SECRET_KEY. app = Flask(__name__) app.secret_key = 'app secret key' Sessions are implemented by default using a cookie signed with the secret key. This ensures t...

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...

A word of caution: AsyncTask has many gotcha's apart from the memory leak described here. So be careful with this API, or avoid it altogether if you don't fully understand the implications. There are many alternatives (Thread, EventBus, RxAndroid, etc). One common mistake with AsyncTask is to c...

when the object is saved/updated, check the associations and save/update any object that require it (including save/update the associations in many-to-many scenario).

Add the following dependency to the build.gradle file: compile 'com.nostra13.universalimageloader:universal-image-loader:1.9.5' Add the following permissions to the AndroidManifest.xml file: <uses-permission android:name="android.permission.INTERNET" /> <uses-permiss...

Here is an example Picasso Circle Transform class based on the original, with the addition of a thin border, and also includes functionality for an optional separator for stacking: import android.graphics.Bitmap; import android.graphics.BitmapShader; import android.graphics.Canvas; import androi...

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...

for loop: arr=(a b c d e f) for i in "${arr[@]}";do echo "$i" done Or for ((i=0;i<${#arr[@]};i++));do echo "${arr[$i]}" done while loop: i=0 while [ $i -lt ${#arr[@]} ];do echo "${arr[$i]}" i=$(expr $i + 1) done Or i=0...

It is very rare that you'll ever want to use Select or Activate in your code, but some Excel methods do require a worksheet or workbook to be activated before they'll work as expected. If you're just starting to learn VBA, you'll often be suggested to record your actions using the macro recorder, t...

Symbol is a new primitive type in ES6. Symbols are used mainly as property keys, and one of its main characteristics is that they are unique, even if they have the same description. This means they will never have a name clash with any other property key that is a symbol or string. const MY_PROP_KE...

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:...

You need to create a new local copy of the repository with the command git svn clone SVN_REPO_ROOT_URL [DEST_FOLDER_PATH] -T TRUNK_REPO_PATH -t TAGS_REPO_PATH -b BRANCHES_REPO_PATH If your SVN repository follows the standard layout (trunk, branches, tags folders) you can save some typing: git svn...

The equivalent to git pull is the command git svn rebase This retrieves all the changes from the SVN repository and applies them on top of your local commits in your current branch. You can also use the command git svn fetch to retrieve the changes from the SVN repository and bring them to ...

The command git svn dcommit will create a SVN revision for each of your local git commits. As with SVN, your local git history must be in sync with the latest changes in the SVN repository, so if the command fails, try performing a git svn rebase first.

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...

static int Sum(int a, int b) { return a + b; } static int Multiplication(int a, int b) { return a * b; } static void Main(string[] args) { Func<int, int, int> method = Sum; // method points to the Sum method // that retuns 1 int variable and takes 2 int vari...