Getting Keyboard Input (So You Can Get a Player's Name)

Input boxes

Getting keyboard input (so you can get a player's name)

It is easy to wait for the player to press a particular key. For example, if we are waiting for the user to press the Escape key, all we have to do is this:

if (kbd.IsKeyDown(Keys.Escape)

prevKbd.IsKeyUp(Keys.Escape) )

However, if we don't know which key the user is going to press next, the problem becomes much more difficult. We have to check ALL keys to see if a key has been pressed.

Using XNA to get string input

Create a new XNA project called InputBoxes. We can use XNA to get string input from a keyboard. Add the following variable declaration at the top of your program:

IAsyncResult keyboardAsyncResult = null;

GamePadState gamePad, prevGamePad;

KeyboardState kbd, prevKbd;

string currentPlayerName = "";

bool nameRequested = false;

enumGameStates

{

SplashScreen,

GetName,

Paused

}

GameStates gameState;

And we will need this statement in our Game1() method:

Components.Add(newGamerServicesComponent(this));

We will use this variable to determine if an input box has been displayed on the screen. If it has a value of null, then no input box has been displayed. If it has a value that is notnull, then the input box is currently being displayed.

XNA allows us to display input boxes that look like this:

Add to Update:

gamePad = GamePad.GetState(PlayerIndex.One);

kbd = Keyboard.GetState();

if (gameState == GameStates.GetName)

{

if (!nameRequested)

{

nameRequested = true;

RequestName();

}

}

UpdateState();

prevGamePad = gamePad;

prevKbd = kbd;

We need a way to determine if we should display an input box. This can be triggered by a key press from the keyboard or a button press on the game pad. The following example uses the space bar or the start button to signal that the input box should be displayed.

Write UpdateState:

void UpdateState()

{

if (!(prevGamePad.Buttons.Start == ButtonState.Released &

gamePad.Buttons.Start == ButtonState.Pressed ||

prevKbd.IsKeyUp(Keys.Space) &

kbd.IsKeyDown(Keys.Space))

)

return;

// We only get this far if space or start has been pressed

if (gameState ==GameStates.SplashScreen)

gameState = GameStates.GetName;

}

To display an input box, use the following command. This is the generic format for the command:

keyboardAsyncResult = Guide.BeginShowKeyboardInput(

PlayerIndex, "Title", "Description", "Default Text",

Callback, State);

Where:

• PlayerIndex is the index of the player providing the input, e.g. PlayerIndex.One
• "Title" is the title (a string) of the dialog box (appears at the top).
• "Description" is the message that is displayed (a string).
• "Default Text" is the text (a string) that is displayed in the user input area at the beginning.
• Callback is the name of the method to be called once the asynchronous method is completed.
• State is a variable we won't worry about. We will always provide the value null.

In our program, we will call BeginShowKeyBoardInput like this:

keyboardAsyncResult = Guide.BeginShowKeyboardInput(

PlayerIndex.One, "Name", "Please enter your name: ",

"", newAsyncCallback(GetName), null);

Now we can write RequestName:

void RequestName()

{

if (keyboardAsyncResult == null)

{

keyboardAsyncResult = Guide.BeginShowKeyboardInput(

PlayerIndex.One, "Name", "Please enter your name: ",

"", newAsyncCallback(GetName), null);

}

}

Write GetName:

void GetName(IAsyncResult result)

{// input box HAS been displayed

if (keyboardAsyncResult != null

& keyboardAsyncResult.IsCompleted)// user is done with input box

{

// Get what the user typed

currentPlayerName = Guide.EndShowKeyboardInput(keyboardAsyncResult);

if (currentPlayerName != null)

{

// Display what the user typed

//Console.WriteLine(message);

currentPlayerName = currentPlayerName.Trim();

Console.WriteLine(currentPlayerName);

keyboardAsyncResult = null;

gameState = GameStates.Paused;

}

}

}

Arguments:

• The first argument is the player providing the input.
• The "Title" is the title of the text box and will appear in its title bar.
• The "Description" is additional text providing instructions to the user and appears below the title box and above the input box's text input area.
• The "Default Text" is what will appear in the input box's text input area.
• The last two arguments are not important for what we are doing and can be left as null values.

2/27/2012Day18--Input-Boxes.docx1