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書名： XNA 4.0 Game Development by Example Beginner's Guide（Visual Basic Edition）
作者名： Kurt Jaegers
本章字數： 194字
更新時間： 2021-08-20 15:50:42

Time for action – falling pieces

Add a new class to the Flood Control project called FallingPiece.
Add the Inherits line after the class declaration as follows:
```
Inherits GamePiece
```

Add the following declarations to the FallingPiece class:

Public VerticalOffset As Integer
Public Shared FallRate As Integer = 5

Add a constructor for the FallingPiece class:

Public Sub New(type As String, verticalOffset As Integer)
    MyBase.New(type)
    Me.VerticalOffset = verticalOffset
End Sub

Add a method to update the piece:

Public Sub UpdatePiece()
    VerticalOffset =
        CInt(MathHelper.Max(0, VerticalOffset - FallRate))
End Sub

What just happened?

Simpler than a RotatingPiece, a FallingPiece is also a child of the GamePiece class. A FallingPiece has an offset (how high above its final destination it is currently located) and a falling speed (the number of pixels it will move per update).

As with a RotatingPiece, the constructor passes the type parameter to its base class constructor, and uses the verticalOffset parameter to set the VerticalOffset member. Again, we use the Me. notation to differentiate the two identifiers of the same name.

Lastly, the UpdatePiece() method subtracts FallRate from VerticalOffset, again using the MathHelper.Max() method to ensure that the offset does not fall below zero.

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

Time for action – falling pieces

What just happened?