Make for loops wait before they loop again

[callum5558]

Hello,
I have been programming a small game for a while. It involves pictures to be constantly moving across the screen. One way to get something to move is to add a timer, and when it ticks add say 5 pixels to the distance between the pic box and the top of the form. Well, while I have been working on this game i have been adding in a fair few timers and different stuff happening when timers tick, and it all got a bit confusing and not working smoothly so I thought I'd try using a while loop.

This is just a test to see if it can work.

Public Class Form1

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        Dim x As Integer = 0

        Do While x = 0

            PictureBox1.Top += 10

        Loop

    End Sub
End Class

So as you can see i'm making the picturebox move downwards while x is equal to 0.

WHAT i want is before it does a loop, it waits a second or however long. If you try this code, you'd see the picturebox moves insanely fast down the form.

My goal is to have it moving down slower like a tetris piece xD

Does anyone know how I could just make it wait a bit?

Cheers, Callum

[Evil_Giraffe]

Nope, that's not going to work. The window isn't going to redraw until the Click event handler has finished running so you won't see it move gradually down the screen, it'll jump there. If you got your delay working then it would just wait longer before jumping to its final position. I would stick to the timer approach, but try and make it all work from a single timer that ticks quite frequently, and only performs the actions relevant at that time.

In fact, to stop a build up of Timer ticks with a small interval that is shorter than the processing time of the tick handler, I would actually have a timer that doesn't continually fire, and the very last thing in the tick event handler is to set the next tick up.

[chris128]

Yeah I agree you need to use a timer instead of a loop. You could use Thread.Sleep(1000) in the loop to pause it for a second but like Evil_Giraffe pointed out, the UI will just freeze and not redraw until it finishes the loop.

PS if in future you ever want a loop to run infinitely like it is in your example, you can just do this instead of using a Do While loop:

Do

  'do something here

Loop

[chad101]

Public Class Form1
    Private m_timer As Timer
    Const constSleepTime As Integer = 500

    Public Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
        m_timer = New Timer With {.Interval = 100}
        AddHandler m_timer.Tick, AddressOf timer_tick

    End Sub
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        m_timer.Enabled = True

        '...Start Loop logic
        .
        .
        .
        'Pause for 500 milliseconds
        System.Threading.Thread.Sleep(constSleepTime)
        .
        .
        '...End Loop logic

        m_timer.Enabled = False
    End Sub

    Private Sub timer_tick(sender As Object, e As System.EventArgs)
        Application.DoEvents()
    End Sub


End Class

[Evil_Giraffe]

No, that won't work chad101. Not only would using Application.DoEvents be a bad idea - if the OP is having difficulty handling multiple timers firing, throwing the problems of re-entrancy from a DoEvents call into the mix is going to cause even more problems.

However, aside from that, it won't work how you've coded it. The timer is started at the beginning of the button click event handler, and is quietly queuing up tick events while the button handler executes. When the button handler finishes executing, the screen can be redrawn, the picturebox jumps to its final position, and then all those tick events are handled and the Application.DoEvents calls are made.

The point of Application.DoEvents is to allow the processing of other messages in the queue whilst you are in the middle of processing a different one. By putting the call to Application.DoEvents inside the processing of a different message, you don't actually interrupt the processing of the blocking message to let that Application.DoEvents run.

[Shaggy Hiker]

While EG covered this indirectly, let me more explicitly point out that thread.Sleep does just that: It puts the thread to sleep for that duration. Since this is the UI thread, NOTHING will be happening during that interval, including responding to any user input, any events (such as timer ticks), or anything else. Sleep is sleep, and it happens at the OS level, so the app doesn't do any backgroud processing of events.

[callum5558]

Cheers guys

Well, thread.sleep was a solution, but as you guys said it freezes the whole program, if in that time i say pressed right to move a picturebox right it wouldn't happen.

I kinda have another query, if you don't mind me asking. I have sort of fixed up my timers problem, but it has made a new issue.
In my form I need to know when two pic boxes intersect, to which then a label in the corner of the form goes from it's current position of health which may be 5, and then 1 is taken away. It looks like this. (This part of code is in a sub that occurs every time a timer ticks)

    Private Sub Timer1_Tick(sender As System.Object, e As System.EventArgs) Handles Timer1.Tick

        If PictureBox1.Bounds.IntersectsWith(PictureBox2.Bounds) Then
            HealthValue -= 1
            Label1.Text = "Health: " & HealthValue.ToString()

        End If

    End Sub

The problem is, due to the timers rate of ticking which has to be high so it's always checking, means that when the picture boxes collide the health amount will go down like 5,4,3,2,1 because the timer is still ticking while the 2 picture boxes are still intersecting as both picture boxes are roughly 70 , 20 in size.

How can i make it so that the very pixel when they first collide, the health is equal to health minus 1 and then even tho the 2 pictureboxes are still intersecting the health doesn't go down by 1?

Help is much appreciated
Callum

[chris128]

Just as a side note, it looks like you're making a game - you might want to consider using the XNA framework which is specifically designed for making games (rather than trying to use WinForms to make a game, which really isn't designed to do that). http://msdn.microsoft.com/en-us/library/bb200104.aspx Although I think it only lets you use C#.NET rather than VB.NET

[ident]

C#.NET

c#.net whats that :O

[chris128]

Oh and as for your question, just use a Boolean variable (True/False) to determine whether or not the images have already intersected. Declare this variable at class level rather than inside your timer tick event, then it will keep its value in between timer ticks. The basic logic would be like this:

IF image 1 intersects with image 2 AND variable is False Then
set variable to true
take away health
End IF

IF they do not intersect Then
set variable to false
End If

[callum5558]

Chris, you've been really great help, cheers!

As this is a school project with a due by date, i'll stick to using vb.net for this project as I havn't learnt much off c#. I'll give XNA a go later.

So if I put the intersects bit of code at a class level, it will keep on checking it? That's pretty cool. When I get up to that part i'll give it a go

Thanks,
Callum

[chris128]

Don't put the entire thing at class level, I just meant the Boolean variable I was talking about. You still need everything else in your timer tick event.

e.g:

Public Class Form1

Dim HasIntersected As Boolean

Sub Timer_Tick
'Do work here and check/set HasIntersected value as described in my previous post
End Sub

End Class