XNA 4.0 Game Development by Example Beginner's Guide（Visual Basic Edition）

上QQ阅读APP看书，第一时间看更新

Time for action – GamePiece class methods – part 3 – connection methods

Add the GetOtherEnds() method to the GamePiece class:

Public Function GetOtherEnds(startingEnd As String) As String()
  Dim Opposites As List(Of String) = New List(Of String)()

    For Each pipeEnd As String In _pieceType.Split(CChar(","))
      If pipeEnd <> startingEnd Then
        Opposites.Add(pipeEnd)
      End If
    Next

  Return Opposites.ToArray()
End Function

Add the HasConnector() method to the GamePiece class:

Public Function HasConnector(direction As String) As Boolean
  Return _pieceType.Contains(direction)
End Function

What just happened?

The GetOtherEnds() method creates an empty List object for holding the ends we want to return to the calling code. It then uses the Split() method of the String class to get each end listed in the _pieceType. For example, the Top,Bottom piece will return an array with two elements. The first element will contain Top, and the second will contain Bottom. The comma delimiter will not be returned with either string.

If the end in question is not the same as the startingEnd parameter that was passed to the method, it is added to the list. After all of the items in the string have been examined, the list is converted to an array and returned to the calling code.

Tip

Type conversion

The Split() method of the String class accepts a Char value, but if we simply supply the comma that we use within quotes (Split(","), for example), the result is itself a String value. This would produce a compiler warning, informing us that we have an implicit conversion from string to char. We need to be careful that we are passing the right types of values to methods, so we are specifically casting the string to a char value using the CChar built-in function. There are a number of these type-conversion functions in Visual Basic that support conversion to various data types, including a CType method that accepts the type you wish to convert to as a parameter.

In the previous example, requesting GetOtherEnds("Top") from a GamePiece with a _pieceType value of Top,Bottom will return a string array with a single element containing Bottom.

We will need this information in a few moments when we have to figure out which pipes are filled with water and which are empty.

The second function, HasConnector(), simply returns true if the _pieceType string contains the string value passed in as the direction parameter. This will allow code outside the GamePiece class to determine if the piece has a connector facing in any particular direction.

Sprite sheet coordinates

Because we set up the PieceTypes array listing the pieces in the same order they exist on the sprite sheet texture, we can calculate the position of the rectangle to draw from based on the _pieceType.