abonament net upc Getting Player Input in Visual Basic .NET

Create UPC A in Visual Basic .NET Getting Player Input

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Figure 3-1

This class contains some variables on the desk (in this case the background color intensities) and two methods, which we have called Mr. Draw and Mrs. Update. Each method has a corresponding telephone. Programs can place calls to the telephones to request that the method perform the required task. The Great Programmer Speaks: Classes Are Not Really Offices Our Great Programmer has been reading these notes and finds them quite amusing. She reckons that classes are not exactly like offices, but she thinks that for the purpose of getting an understanding of how programs are constructed, it s okay to regard them as such. When an XNA game starts, the XNA system makes an instance of the Game1 class that it can then ask to Draw and Update. When an instance of a class is created, the statements for the methods it contains are loaded into memory, and space is set aside for the data variables that the instance holds. The class files that you write give the plans for the class so when the program runs instances of each class can be created. In real life you would make a game office by building a room, putting a desk and some telephones in, and then hiring a Mr. Draw and a Mrs. Update. The process of making an instance of a class is similar. However, to save memory, the running program will only use one copy of the method code that is shared between all the instances of a class. Note

It s important to remember that this happens when a program runs. The process of creating instances of classes is not performed by the compiler. The job of the compiler is to convert your C# source code into instructions that the computer or Xbox can run. By the time that your program has control, the compiler has done its job, and the computer or Xbox is just running the machine language output that the compiler produced.

XNA also looks after a lot of other things when a game is running, and one of these is the GamePad class connected to all the gamepads. You don t have to know how the gamepad is actually connected; for all you know, it might use tiny pixies traveling up and down the wires carrying pixie notes written on pixie paper saying Master has pressed the Red Button, but then again it might not. Figure 3-2 shows how the GamePad class would look if it were an office.

Figure 3-2

The GamePad class contains a method called GetState that will get the state of one of the gamepads. When GetState is called, it looks at one of the gamepads, reads its settings, and then sends information back. The GetState method is supplied with a parameter that identifies the gamepad to be read. A parameter is a way that a call can give information to a method. You have seen these before; in your very first programs, you were passing Color parameters into the Clear method to select the color of the screen that you wanted. In the case of the GetState method, the parameter identifies the gamepad that you want to read. If you re thinking in terms of offices, you can think of a parameter as part of the instructions that come down the telephone. When the phone rings and Mr. GetState answers it, he is

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asked to get me the state of gamepad 1. The information about the state of the gamepad is sent back in a GamePadState structure, which is shown in Figure 3-3.

GamePadState Buttons A B X Y Start Back ButtonState.Pressed ButtonState.Released ButtonState.Released ButtonState.Released ButtonState.Released ButtonState.Released

Figure 3-3