问题
I'm trying to make the classic Snake game in VB.NET, but if I hold a key (any key) during the game, after a few seconds the game freezes until I release the key. I've tried lots to fix this, but nothing works, maybe because I don't understand the problem.
I'm assuming that when I hold down a key, the Form1_KeyDown function gets called, and when, after a few seconds, the key goes into "I'm being held down" mode, that function is constantly called, so the timers don't get a chance to update. But like I said, I'm probably wrong.
Any help at all would be appreciated, I've been struggling with this for a while. I think this is all the necessary code, please let me know if it isn't.
Code for key down event:
Private Sub Form1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown
' Sorts out all the key presses: movement, resetting, pausing
' Change direction, unless the player tries to travel backwards into themself
Select Case e.KeyCode
Case upKey
If previousDirection <> "D" Then
nextDirection = "U"
End If
Case leftKey
If previousDirection <> "R" Then
nextDirection = "L"
End If
Case rightKey
If previousDirection <> "L" Then
nextDirection = "R"
End If
Case downKey
If previousDirection <> "U" Then
nextDirection = "D"
End If
Case resetKey
resetGame()
Case pauseKey
paused = Not paused
If paused Then
lblPaused.Visible = True
tmrTime.Stop()
tmrFruit.Stop()
tmrMove.Stop()
Else
lblPaused.Visible = False
tmrTime.Start()
tmrFruit.Start()
tmrMove.Start()
End If
End Select
End Sub
Code for the timer that updates/moves the snake (I'm aware this is really inefficient):
Private Sub tmrMove_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tmrMove.Tick
' Adds a new head in direction of travel, and removes the tail, giving the illusion of snake movement
Dim head As Object = bodyParts(bodyParts.Count - 1)
Dim tail As Object = bodyParts(0)
Dim newHead As Object
head.Text = ""
' Add new head
Select Case nextDirection
Case "R"
' If snake goes out of bounds
If head.Tag(0) + 1 >= numberOfColumns Then
newHead = grid(0, head.Tag(1))
If newHead.BackColor = snakeColor Then
killSnake()
End If
Else
' If snake overlaps itself
If bodyParts.Contains(grid(head.Tag(0) + 1, head.Tag(1))) Then
killSnake()
Exit Sub
Else
' If snake is fine
newHead = grid(head.Tag(0) + 1, head.Tag(1))
End If
End If
' If fruit taken
If newHead.BackColor = fruitColor Then
eatFruit(newHead, tail)
End If
Case "L"
If head.Tag(0) - 1 < 0 Then
newHead = grid(numberOfColumns - 1, head.Tag(1))
If newHead.BackColor = snakeColor Then
killSnake()
End If
Else
If bodyParts.Contains(grid(head.Tag(0) - 1, head.Tag(1))) Then
killSnake()
Exit Sub
Else
newHead = grid(head.Tag(0) - 1, head.Tag(1))
End If
End If
If newHead.BackColor = fruitColor Then
eatFruit(newHead, tail)
End If
Case "U"
If head.Tag(1) - 1 < 0 Then
newHead = grid(head.Tag(0), numberOfRows - 1)
If newHead.BackColor = snakeColor Then
killSnake()
End If
Else
If bodyParts.Contains(grid(head.Tag(0), head.Tag(1) - 1)) Then
killSnake()
Exit Sub
Else
newHead = grid(head.Tag(0), head.Tag(1) - 1)
End If
End If
If newHead.BackColor = fruitColor Then
eatFruit(newHead, tail)
End If
Case "D"
If head.Tag(1) + 1 >= numberOfRows Then
newHead = grid(head.Tag(0), 0)
Else
If bodyParts.Contains(grid(head.Tag(0), head.Tag(1) + 1)) Then
killSnake()
Exit Sub
Else
newHead = grid(head.Tag(0), head.Tag(1) + 1)
End If
End If
If newHead.BackColor = fruitColor Then
eatFruit(newHead, tail)
End If
Case Else
newHead = grid(head.Tag(0), head.Tag(1))
End Select
bodyParts.Add(newHead)
newHead.BackColor = snakeColor
newHead.Font = headFont
newHead.Text = headText
' Remove tail
tail.BackColor = gridColor
bodyParts.RemoveAt(0)
previousDirection = nextDirection
End Sub
回答1:
I'm assuming that when I hold down a key, the Form1_KeyDown function gets called, and when, after a few seconds, the key goes into "I'm being held down" mode, that function is constantly called, so the timers don't get a chance to update. But like I said, I'm probably wrong.
In fact, you are right.
In Windows you'll get a WM_KEYDOWN message as soon as the key is pressed, and then, after a certain interval, you'll be getting lots of WM_KEYDOWN messages with another certain interval between them.
You can find these intervals if you go to Control Panel - Keyboard.
The easiest way of fixing it is adding a call to DoEvents in the end of the key handler.
Try removing the keydown handler completely. Instead, figure nextDirection in the beginnig of tmrMove_Tick by examining Keyboard.IsKeyDown.
Try removing the keydown handler completely. Instead, figure nextDirection in the beginning of tmrMove_Tick by examining GetAsyncKeyState, which you can declare as follows:
Private Declare Function GetAsyncKeyState Lib "user32" Alias "GetAsyncKeyState" (ByVal vKey As Keys) As Short
Private Shared Function IsKeyDown(ByVal Key As Keys) As Boolean
Return (GetAsyncKeyState(Key) And &H8000S) = &H8000S
End Function
回答2:
I would recommend trying the keyup event instead. It won't spam like the keypress nor keydown events
回答3:
You are correct with the problem being with the key repeating. I have in the past used a variable to hold the previous keystate and exit the keypressed event if it is the same. I am reseting this with a timer that should get you enough of a delay.
If oldKeyData = e.KeyCode Then
e.Handled = True
Exit Sub
End If
oldKeyData = e.KeyCode
tmrKeyReset.Enabled = True
Edit: @SpectralGhosts answer will work if you want to move with individual key presses.
来源：https://stackoverflow.com/questions/8626110/why-does-my-vb-net-snake-game-freeze-when-i-hold-a-key-down