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Dates and times are presented in many different ways across the globe, making them a difficult challenge for developers Although Qt provides classes to handle the complexity, there is a risk of misinterpreting user input and confusing the user through output Let s start by having a look at time and how it is presented to the user Time expressed as text is often presented as a digital clock, with two digits for hours and two digits for minutes The hours and minutes are separated by a colon or a simple dot The issue here is that the clock can be of the 24-hour type, where the hours run from zero to 23 The clock can also be of the 12-hour type, where the hours run from zero to 11 twice.

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First, as Example 3-36 shows, we ll delete the special constructor from Plane, and then make Identifier an ordinary read/write property. We can also remove the _identifier backing field we added earlier, because we ve gone back to using an auto property.

class Plane { // Remove the constructor that we no longer require // public Plane(string newIdentifier) // { // Identifier = newIdentifier; // } public string Identifier { get; // remove the access modifier // to make it public set; } } // ...

We can now use the object initializer syntax for all the properties we want to set. As Example 3-37 shows, this makes our code look somewhat neater we only need one style of code to initialize the object.

In the latter case, the minutes are followed by AM or PM, indicating whether the time indicates a time in the morning or in the evening You can handle both input and output in the way that the user expects with the QTime methods toString and fromString (in combination with the timeFormat method of the QLocale class) or by using the toString method from QLocale directly Just make sure that you do not interpret a PM time from a 12-hour clock as a time for a 24-hour clock followed by some nonsense characters Listing 10-15 shows a function that prints times using given locales The resulting output is shown in Listing 10-16 The locales are QLocale( QLocale::Swedish, QLocale::Sweden ) and QLocale( QLocale::English, QLocale::UnitedStates ) Listing 10-15.

Plane someBoeing777 = new Plane { Identifier = "BA0049", Direction = DirectionOfApproach.Approaching, SpeedInMilesPerHour = 150 };

Object initializer syntax provides one big advantage over offering lots of specialized constructors: people using your class can provide any combination of properties they want. They might decide to set the Position property inline in this object initializer too, as Example 3-38 does if we d been relying on constructors, default or named arguments wouldn t have helped if there was no constructor available that accepted a Position. We ve not had to provide an additional constructor overload to make this possible developers using our class have a great deal of flexibility. Of course, this approach only makes sense if our type is able to work sensibly with default values for the properties in question. If you absolutely need certain values to be provided on initialization, you re better off with constructors.

Plane someBoeing777 = new Plane { Identifier = "BA0049", Direction = DirectionOfApproach.Approaching, SpeedInMilesPerHour = 150, Position = new PolarPoint3D(20, 180, 14500) };

In the following sections, you ll learn how to use JavaScript in Atlas by creating your first Atlas application.

So, we ve addressed the data part of our Plane; but the whole point of a class is that it can encapsulate both state and operations. What methods are we going to define in our class

Printing times using different locales void printTimes( QLocale loc ) { QLocale::setDefault( loc ); QTime t1( 6, 15, 45 ); QTime t2( 12, 00, 00 ); QTime t3( 18, 20, 25 ); qDebug() qDebug() qDebug() qDebug() << << << << "short"; loctoString( t1, QLocale::ShortFormat ); loctoString( t2, QLocale::ShortFormat ); loctoString( t3, QLocale::ShortFormat );.

When deciding what methods a class might need, we generally scan our specifications or scenarios for verbs that relate to the object of that class. If we look back at the ATC system description at the beginning of this chapter, we can see several plane-related actions, to do with granting permissions to land and permissions to take off. But do we need functions on the Plane class to deal with that Possibly not. It might be better to deal with that in another part of the model, to do with our ground control, runways, and runway management (that, you ll be pleased to hear, we won t be building). But we will periodically need to update the position of all the planes. This involves changing the state of the plane we will need to modify its Position. And it s a change of state whose details depend on the existing state we need to take the direction and

speed into account. This sounds like a good candidate for a method that the Plane class should offer. Example 3-39 shows the code to add inside the class.