I would like to use the following code in C# but I just can't seem to get out of it. I would like to terminate the application if the user presses a key or moves the rodent (aka mouse). Here is my code (no laughing!).
private void frmDots_KeyDown(object sender, KeyEventArgs e)
{
bgNotClicked = false;
Close();
}
private void frmDots_Click(object sender, EventArgs e)
{
bgNotClicked = false;
Close();
}
while (bgNotClicked)
{
// Clear the first element in our XY position. This is the reverse of the way I normally create the dots application
System.Drawing.Rectangle clearDots = new System.Drawing.Rectangle(Dots.PositionX[iCounter], Dots.PositionY[iCounter], 8, 8);
// Create the black color and brush to clear dots
Color clearDotsColor = Color.Black;
SolidBrush clearDotsBrush = new SolidBrush(clearDotsColor);
// Finally clear the dot
e.Graphics.FillEllipse(clearDotsBrush, clearDots);
GetRandomPosition(iCounter);
// Fill the elements to display colors on the displays canvas
System.Drawing.Rectangle colorDots = new System.Drawing.Rectangle(Dots.PositionX[iCounter], Dots.PositionY[iCounter], 8, 8);
// Create the color and brush to show dots
Color colorRandom = GetRandomColor();
SolidBrush colorBrush = new SolidBrush(colorRandom);
// Finally show the dot
e.Graphics.FillEllipse(colorBrush, colorDots);
Thread.Sleep(5);
iCounter++;
if (iCounter == 399)
{
iCounter = 0;
}
}
}
Your "busy waiting" strategy is poor design. Instead, you should use event handlers that are fired:
On keypress.
When the mouse is moved.
In either case, you can respond by terminating the application.
Edit:
After seeing your edit, this is definitely your problem. The issue is that your while loop blocks the main UI thread, so it never handles the Windows Messages which trigger your key press/mouse/etc handlers.
You have a couple of options - you can either move some of this onto a separate thread, do what I suggested below, or add a call to Application.DoEvents in your while loop. This would allow your event handlers to run, which would in turn set bgNotClicked = false;. Right now, that's never occurring because your UI is blocked entirely.
Original Post:
If you're doing this loop in your UI thread, you're going to need to rethink the design a bit.
Setting bgNotClicked = false; somewhere in an event handler will work, but only if your event handler is able to run. If you're doing the above code in the UI thread, it will block your UI thread indefinitely, preventing the event handler from firing.
I would recommend reworking this to be based off a timer (so it runs repeatedly on regular intervals), instead of locked into a while loop. This would allow your other UI events to fire between runs, and instead of setting bgNotClicked = false;, your event handler could just set the timer to be not enabled.
Your bgNotClicked variable needs to be set to false by your event handler for key-press.
If the rodent is moved by your mouse, you would need a similar mouse event handler.
The break keyword will terminate a loop. In this case, when you hit the case where you want to stop the loop, you would just use break;.
If you're looping like that you need to give the application a moment to process the events that you're hoping will cause the interruption. This is the job of the DoEvents method.
private bool WeAreDone = false;
private void DoingIt()
{
while (true)
{
Application.DoEvents();
if (WeAreDone)
{
break;
}
}
}
private void InterruptButton_Click(object sender, EventArgs e)
{
WeAreDone = true;
}
I think using a Timer fits the Windows event-driven model better than the busy wait while loop. You might try something like this:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private int iCounter = 0;
private void Draw()
{
// ....
}
private void timer1_Tick(object sender, EventArgs e)
{
Draw();
iCounter++;
if(iCounter == 399)
{
iCounter = 0;
}
}
private void Form1_Load(object sender, EventArgs e)
{
timer1.Interval = 5;
timer1.Enabled = true;
}
private void Form1_Click(object sender, EventArgs e)
{
timer1.Enabled = false;
Close();
}
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
timer1.Enabled = false;
Close();
}
}
This does not seems to be the correct way. .Net Framework has provided you with the events to handle the KeyPress and MouseMove/Click actions. Why are you not using them?
Try moving the loop into a BackgroundWorker's DoWork event handler. Then your GUI will still be responsive and instead of that nasty variable, you can just call the CancelAsync method to stop the loop.
You can exit the loop using the break statement.
EDIT: OK, I take back the flag thing!
Use Environment.Exit(2); (or Environment.Exit(1) it really doesn't make a difference) to exit out of the application.
Exit While
...................
Related
Sorry, this may be a duplicate question, but I couldnot understand the solutions already provided in different answers.
I have created a mp3 player in a different manner, it plays one mp3 file at a time but one listbox have the chapters, which is not only handling to move position of that particular mp3 but also changes a picturebox image. Now somewhere I need to change the selection of the listbox from a seekbar but dont want to fire the following event of;
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
Please guide.
One way to inhibit your selection indexed change event doing its normal way is to use a boolean flag. Also, make sure that this inhibition does not stay around when some exception is raised:
private bool inhibit = true;
private void doSomeProcessWithInhibit()
{
try
{
inhibit = true;
// processing comes here
}
// if something goes wrong, make sure other functionality is not blocked
finally
{
inhibit = false;
}
}
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
// fast return to reduce nesting
if (inhibit)
return;
// do event handling stuff here
}
P.S. Try to use meaningful names for controls (check listBox1). You will thank yourself when revisiting the code and/or others have to.
Add a Boolean with class scope called something like isProcessing. Set it to true. Do your work, then set it to false. Warp your event in the Boolean:
bool isProcessing = true;
private void switchControls(){
isProcessing = true;
//do work;
isProcessing = false;
}
private void MyControl.OnEvent(object sender, EventArgs e){
if(!isProcessing){
//what you would normally do
}
}
OR....
Deregister the event, the re-register it
private void switchControls(){
myButton1.OnClick -= myButtonClick;
//do work
myButton1.OnClick += myButtonClick;
}
I have a form with two text fields, A and B that are supposed to behave in the following way:
Typing something into A should set B.Text = f(A.Text)
Typing something into B should set A.Text = g(B.Text)
...for some arbitrary and potentially unrelated functions f and g.
The problem I'm facing is that the naive implementation of simply throwing the above code into each field's handler will create an infinite loop as A's handler will update B's value and call B's handler, which will update A, etc.
What would be the correct (and preferably thread-safe) way to handle this? Either somehow determining whether a change was done manually or programmatically, somehow suppressing events firing when changing the value, or some other way.
Use a flag to signal that you are doing changes
private bool updating;
private void A_TextChanged(object sender, EventArgs e)
{
if (!updating) {
updating = true;
B.Text = f(A.Text);
updating = false;
}
}
private void B_TextChanged(object sender, EventArgs e)
{
if (!updating) {
updating = true;
A.Text = g(B.Text);
updating = false;
}
}
You don't have to care about thread-safety as this all happens in the unique UI-thread. UI events never create new threads; i.e. an event (click, text changed, etc.) never interrupts another one!
If you want to be sure that the flag is reset, you can use the try-finally statement. The finally block is ensured to run, even if an exception should occur within the try block (unless the application is terminated unexpectedly).
if (!updating) {
updating = true;
try {
A.Text = f(B.Text);
} finally {
updating = false;
}
}
I assume you're using TextChanged event, try this then:
private bool callB=true;
private bool callA=false;
private void A_Click(object sender, System.EventArgs e)
{
callB=true;
callA=false;
}
private void B_Click(object sender, System.EventArgs e)
{
callB=false;
callA=true;
}
private void A_textchanged(object sender, RoutedEventArgs e)
{
if(callB)
B.text=f(A.text);
}
private void B_textchanged(object sender, RoutedEventArgs e)
{
if(callA)
A.text=g(B.text);
}
Anyway, a better way to just edit A when the user is finished with B(finished whatever he wanted to write in it), that's because if expression will be evaluated at every character the user inputs.
By the way, changing a text while the user writes might be surprising to him, so better to avoid textchanged event in this case.
I have a question regarding looping with button click event, I've tried many methods & searched many pages in search for a simple answer for the past hour, but the truth is each answer just looks like alien code, probably because I'm still very new to developing.
Here's a simplified version of what I'm trying to do :
private string Message = "Hello";
private void Spam(bool loop)
{
if (loop == true)
{
while (loop == true)
{
MessageBox.Show(Message);
}
}
else { MessageBox.Show("Spamming has stopped !! "); }
}
private void button1_Click(object sender, EventArgs e)
{
Spam(true);
}
private void button2_Click(object sender, EventArgs e)
{
Spam(false);
}
Obviously this isn't my API, or it'd be a useless thing to invent, however, the code itself is long & you guys always ask for "relevant code" (No disrespect), so there it is.
My problem : Breaking out of the spam loop upon clicking button 2, the code to me looks decent enough for the API to figure out, but each time button 1 is clicked, the API freezes.
Use a background worker to do your work. You can use the cancellation feature to break out of it when you're done. Your loop as you have it will block the UI thread when executed syncronously, which is why your GUI becomes unresponsive. Note if you do any interaction with the UI in the do work delegate, you need to marshal back onto the UI thread (via invoke for example).
private BackgroundWorker _worker = null;
private void goButton_Click(object sender, EventArgs e)
{
_worker = new BackgroundWorker();
_worker.WorkerSupportsCancellation = true;
_worker.DoWork += new DoWorkEventHandler((state, args) =>
{
do
{
if (_worker.CancellationPending)
break;
Console.WriteLine("Hello, world");
} while (true);
});
_worker.RunWorkerAsync();
goButton.Enabled = false;
stopButton.Enabled = true;
}
private void stopButton_Click(object sender, EventArgs e)
{
stopButton.Enabled = false;
goButton.Enabled = true;
_worker.CancelAsync();
}
Update 2019:
BackgroundWorker is now largely obsolete, replaced by the async/await feature in later versions of C# which is easier to use. Here is an example of how to achieve the same thing using that feature:
private CancellationTokenSource _canceller;
private async void goButton_Click(object sender, EventArgs e)
{
goButton.Enabled = false;
stopButton.Enabled = true;
_canceller = new CancellationTokenSource();
await Task.Run(() =>
{
do
{
Console.WriteLine("Hello, world");
if (_canceller.Token.IsCancellationRequested)
break;
} while (true);
});
_canceller.Dispose();
goButton.Enabled = true;
stopButton.Enabled = false;
}
private void stopButton_Click(object sender, EventArgs e)
{
_canceller.Cancel();
}
There's one important thing to remember:
While your code is being executed, the user cannot interact with your user interface.
That means: You first need to exit the loop (i.e. return from the Spam method), and then the user can click Button2.
That's a hard truth, because it means you cannot write the code in the way you wanted to. Fortunately, there are a few ways to work around that:
Don't use a loop. Use some kind of timer to do the "spamming". Button1 starts the timer, Button2 stops it. What kind of timer is available depends on the user interface library you use (WinForms has a Timer, WPF has a DispatcherTimer).
Do the "spamming" in a background thread. This will allow your user interface to stay responsive, and you can communicate with the background thread, for example, by setting a volatile Boolean. This, however, is an advanced topic (and can quickly lead to complex synchronization issues), so I suggest that you try the other option first.
When you click button1 the Spam method is called and loop is starting. When you click button2 Spam method is called but it's not the same. It's the second execution, so it will check the condition and won't enter into the loop, but the loop in the first call sill will be running.
You should use a flag and the loop should use that flag to determine whether it should be still running. It should look something like that:
bool run = false;
string message = "This API is not original";
private void Spam()
{
while (run == true)
{
MessageBox.Show(message);
}
}
}
private void button1_Click(object sender, EventArgs e)
{
message = "Hellooo";
flag = true;
Spam();
}
private void button2_Click(object sender, EventArgs e)
{
flag = false;
}
Take a look at this concept:
private bool loop = false;
private void Start()
{
loop = true;
Spam("Some Message??");
}
private void Spam(string message)
{
while (loop)
{
MessageBox.Show("This API is not original");
}
}
private void button1_Click(object sender, EventArgs e)
{
loop = true;
}
private void button2_Click(object sender, EventArgs e)
{
loop = false;
}
However, the user won't be able to press a button if a MessageBox keeps popping up as it takes up the main UI thread. In order to prevent this you could use BackgroundWorker or start a new thread.
private void AddMyScrollEventHandlers()
{
VScrollBar vScrollBar1 = new VScrollBar();
}
private void button1_Click(object sender, EventArgs e)
{
while (true)
{
if (vScrollBar1.Value + 1 < vScrollBar1.Maximum)
{
vScrollBar1.Value = vScrollBar1.Value + 1;
label1.Text = vScrollBar1.Value.ToString();
}
else
{
break;
}
System.Threading.Thread.Sleep(200);
}
}
private void button2_Click(object sender, EventArgs e)
{
// vScrollBar1.Scroll
}
I am new in C#. I was working on scroll. What I wanted here is, if anyone click button1 then scroll automatically move to the end and I wanted to show gradual value in label1. Also when someone click button2 scrolling stop.
Now the problem is label1 do not show gradual change in value. It shows value once when the scrolling stop.
Also when scrolling continue i,e when while loop is working I can not click on button2. Actually I can not click on the form even.
Someone please give me some idea how to do this.
This happens because the thread that is performing the task is busy, and it's the same thread that updates the UI. You can use a multithreading solution. Take a look at
BackgroundWorker
All the UI events run in the main thread of the application, so the application can only process one event at a time. When the application is processing an event, no other event will be processed.
Since you are doing a UI related work periodically, the best option is to use the Timer class:
Drop Timer from the toolbox into the form.
In the properties window, set the interval to 200.
Double click the timer object to create the Tick event handler.
Put this code in the newly created timer1_Tick method:
if (vScrollBar1.Value + 1 < vScrollBar1.Maximum)
{
vScrollBar1.Value = vScrollBar1.Value + 1;
label1.Text = vScrollBar1.Value.ToString();
}
else
{
timer1.Stop();
}
Change your methods as below:
private void AddMyScrollEventHandlers()
{
timer1.Start();
}
private void button2_Click(object sender, EventArgs e)
{
timer1.Stop();
}
Now you're done.
I would recommend using BackgroundWorker control, as suggested by Agustin Meriles. However, one more important thing to note is that You should use Control.Invoke(...) method to update controls from another thread.
I've modified Your code, tested it in a sample application and it seems to work correctly.
First, add a new BackgroundWorker control to Your form and assign backgroundWorker1_DoWork to its DoWork event.
Then, You can use the code below:
private void button1_Click(object sender, EventArgs e)
{
//code from here is moved to BackgroundWorker control
backgroundWorker1.RunWorkerAsync();
}
private void button2_Click(object sender, EventArgs e)
{
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
//while (true)
//the condition directly in the while looks more clear to me
while (vScrollBar1.Value + 1 < vScrollBar1.Maximum)
{
//update controls using Invoke method and anonymous functions
vScrollBar1.Invoke((MethodInvoker)delegate() { vScrollBar1.Value += 1; });
label1.Invoke((MethodInvoker)delegate() { label1.Text = vScrollBar1.Value.ToString(); });
//when called inside BackgroundWorker, this sleeps the background thread,
//so UI should be responsive now
System.Threading.Thread.Sleep(200);
}
}
If You have any problems when using this code, please let me know.
Update
As mentioned in the comments, You could also use ProgressChanged event of the BackgroundWorker. It requires some more changes in the code, but is more suitable in this case. You can find some information about it here: http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.progresschanged.aspx.
If You are not going to add any other code with more processing in the while loop, You can also use Timer control, as suggested by MD.Unicorn in his answer.
I've a backgroundworker which take care of a timer in my application. This is the code:
protected override void OnLoad(EventArgs e)
{
// Inizializzo il backgroundworker
bgwTimer.WorkerReportsProgress = true;
bgwTimer.WorkerSupportsCancellation = true;
bgwTimer.DoWork += (bgwTimer_DoWork);
bgwTimer.RunWorkerCompleted +=(bgwTimer_RunWorkerCompleted);
bgwTimer.ProgressChanged += (bgwTimer_ProgressChanged);
}
void bgwTimer_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
throw new NotImplementedException();
}
void bgwTimer_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
throw new NotImplementedException();
}
Basically the event "ProgressChanged" is never fired and so I cannot update the status of a progressbar.
The event DoWork is linked to this method:
void bgwTimer_DoWork(object sender, DoWorkEventArgs e)
{
int i = 0;
if (bgwTimer.CancellationPending)
{
e.Cancel = true;
}
else
{
while (bgwTimer.IsBusy)
{
Thread.Sleep(1000);
bgwTimer.ReportProgress(i);
refreshTimer();
}
}
}
By my side the code looks good and it runs fine. As you can see the ReportProgress method is called but the event is not fired. Any hints?
UPDATE:
Whops! I found that the event "bgwTimer_ProgressChanged" is fired only if I run the RunWorkerAsync right after the declaration of event. Basically:
bgwTimer.ProgressChanged += (bgwTimer_ProgressChanged);
bgwTimer.RunWorkerAsync(); //this works!
Since I run the worker when the user press a button, the event is not triggered.
Here's the code of click event button:
private void btnNext_Click(object sender, EventArgs e)
{
this.TopMost = true;
btnNext.Enabled = false;
progressBar1.Step = 0;
if (_bgwTimer.IsBusy)
_bgwTimer.CancelAsync();
else
_bgwTimer.RunWorkerAsync();
}
Put a breakpoint, or a Debug.Print or System.Windows.Forms.Messagebox just before bgwTimer.ReportProgress(i), to verify that you're actually entering the while loop.
Note that the BackgroundWorker is not actually a timer; it's a wrapper for a thread that provides a threadsafe invoking layer for your user interface.
Your if (bgwTimer.CancellationPending) { } should be inside the while loop, not outside it. It will only get checked once in your current code.
Note that, if you're inside the DoWork event handler, then by definition you're running an asynchronous process, so IsBusy should always be true (according to the MSDN documentation), and therefore your while is an infinite loop. But check it with your debugger.
It's not raising the event because the value of i is always zero, which is helpfully undocumented but I found out the same thing when building a background worker a while back.
You forgot to start the worker. Add this line to your OnLoad() method:
bgwTimer.RunWorkerAsync();
In the DoWork-Method replace bgwTimer through ((BackgroundWorker)sender). Maybe this is the problem