I have a grid and when a row is double clicked a form is loaded. However a lot of data must be loaded, so I'd like to display a simple form with the text 'loading, please wait..'. And when all loading is finished, the form must disappear.
This is what I have right now, but it doesn't work:
Code that invokes the form with lots of data:
FormWithLotData form = new FormWithLotData();
form.ShowDialog(this);
Constructor of FormWithLotData:
// Show load form
FormIsLoading frm = new FormIsLoading();
_CloseLoadForm closeForm = new _CloseLoadForm(frm.Close);
System.Threading.Thread thread = new System.Threading.Thread(frm.Show);
thread.Start();
InitializeComponent();
this.Visible = false;
LoadAllData();
this.Visible = true;
// Close load form
Invoke(closeForm);
Hope you can help me out.
EDIT:
I'd like to show an animated gif on the loading form.
SOLUTION:
I've created a background worker. The DoWork event handles all the loading and by using the invoke() method I add nodes to the treeview. Now, the GUI doesn't hang and the user don't have the idea that the application is hanging.
You need to reverse your code.
The constructor of FormWithLotData is running in the UI thread. This is the thread that must show your FormIsLoading form. So instead of trying to display this form using the new Thread, do your data loading with it.
The DoEvents way others have suggested is the easiest to implement and (possibly? never done it myself) may work well.
The better pattern to use is to do your data loading on a worker thread. Before you show your FormWithLotData, Begin loading data on a background thread and show your Loading dialog. The method that loads the data should have a callback method into the Loading dialog to signal when it should Close(). Once it closes you can then construct a new FWLD, pass it the already loaded data, and Show it.
Trying to load your data after the form has already been invoked mixes your UI with your data operations, forcing your form to not only be in charge of the UI but also be in charge of data retrieval. Bad for KISS and Single Responsibility, imho.
After your update, it seems like DoEvents is going to be the only real answer to your question, but with some caveats.
You will not be able to show another form MODALLY while you construct your tree. You will still have to do your heavy work within your form's constructor. You will still have to hide your main form and Show() (not ShowDialog) your loading form. You will also have to call DoEvents at every single possible moment while constructing your tree. Its not exactly an elegant solution, but it will probably be your best bet at this point.
how about ...
FormIsLoading frm = new FormIsLoading();
frm.Show();
Application.DoEvents();
// ... load data ...
frm.Close();
In the Form_Load event, add the following:
this.Visible = true;
Application.DoEvents();
before any other processing occurs. The Application.DoEvents caused the UI to show the form at the current state, where normally the UI thread is locked while you other processing is taking place.
Don't do your LoadAllData() directly in a UI thread, instead start up a background thread to do it. The in your Form_Loaded event handler, use an AutoResetEvent and wait till it becomes signalled by the background data retrieving thread. Once it is signalled you can then continue to do whatever you need to do with the data, like bind it into the UI.
This method is still a little clunky for various reasons, but it will get you started.
Edit: i was being lazy with my answer above... a better option is to pass a delegate (callback) to the background thread, when the delegate is invoked (upon completion of the data retrieval) it marshals itself back on to the UI thread, and starts doing the required work with the data.
Inside your form, you can use a Timer control to simulate loading
using ProgressBar when it reaches 100 it unloads the form or any
kind of animation.
for progress-bar code just add the control from the toolbox and then
write the following code:
ProgressBar1.Value = ProgressBar1.Value+1;
if(ProgressBar1.Value == 100)
{
timer1.Enabled = false; this.Hide();
MessageBox.Show("Complete Loading...");
}
Related
I have a button in a form. When the button is clicked, the button click function is called. In the function at first another form (let's call it object form2 from class Form2) it is created with some objects including labels and progress bars (these objects are created through form2 constructor). Then form2.Show() is called. Then a while loop comes which by end of it some variables are updated. I use these variables to update several objects in form2. The problem is that the form objects are not shown rightly until the button click function is finished. For example instead of labels, white rectangles are shown. I tried using Thread.Sleep(1000) after my while to see if objects are shown rightly but it didn't have any effect on form2 shape. Then I used a MessageBox.Show() after my while and it worked surprisingly! Objects were shown correctly in form2.
I appreciate if anyone could say what is the problem and how I can solve it.
You're blocking the UI thread, thus preventing updates until you release the UI thread to continue handling other messages sent to it.
If you have long running CPU bound work, you should be offloading it to another background thread. If you have IO or other non-CPU bound work to do you should be doing it asynchronously, rather than synchronously blocking on it, so that the UI thread can continue processing other events.
If you do heavy work you really should do it in a background worker.
Meanwhile (to get it work) you can call Application.DoEvents which should give your controls "time" to update.
Taken from MSDN:
http://msdn.microsoft.com/en-us/library/system.windows.forms.application.doevents%28v=vs.110%29.aspx
foreach (string file in files )
{
System.IO.FileInfo fileInfo = new System.IO.FileInfo(file);
System.IO.FileStream fileStream = fileInfo.OpenRead();
pictureBox1.Image = System.Drawing.Image.FromStream(fileStream);
Application.DoEvents();
fileStream.Close();
// Call Sleep so the picture is briefly displayed,
//which will create a slide-show effect.
System.Threading.Thread.Sleep(2000);
}
If you are interested in more details, Hans has a good explanation: https://stackoverflow.com/a/5183623/2243584
One could always argue about the use of Application.DoEvents but as Hans stated ShowDialog uses it internally as well - thats the reason why your MessageBox example worked!
Form1.button_Click(...) {
// Show a dialog form, which runs a method <CheckBalance()> on it's OnLoad Event.
var modemDialog = new ModemDialog("COM25");
modemDialog.ShowDialog();
// the user can't see this dialog form until the method <CheckBalance()> terminates.
}
Is it possible to show first the dialog then run the specified method?
THanks.
That is correct and expected. Winforms UI is inherently single-threaded. Having a function call like "CheckBalance" in the form load event will prevent the form from showing until the form load event completes. Depending on the duration of the task, you have a number of options available to you:
If it's a fast task, compute it ahead of time before showing the form
If it's something the user may want to initiate, move it to a button on the new form, so it's only calculated on the request of the user
If it's a long running task that takes some time, you'll need to move it off in to another thread. Using a BackgroundWorker is recommended.
OnLoad occurs before the form is shown to allow you to initialise the form and variables and what not, which means it is synchronous. The form will not show until you return from that function.
If you want to asynchronously run the CheckBalance() method, then you can use a few techniques, such as utilising the Threading, ThreadPool or Tasks API to shift that work to a background thread, and returning immediately so that the form is shown.
Here is an example of using a Task to perform the same action, but asynchronously so that the form immediately shows:
Action<object> action = () => { CheckBalance(); };
new Task(action).Start();
Please note that if you access the UI thread, you'll need to beware of thread-safety and invocation.
The simple way to make sure your form is visible before CheckBalance is run is to use this code in the form load handler:
this.BeginInvoke((Action)(() => this.CheckBalance()));
This will push the execution of the CheckBalance method onto the UI thread message pump so will execute after all preceding UI code is complete.
Others are correct though that the UI will still be blocked as CheckBalance executes. You probably want to run it on a background thread to prevent this.
Am relatively new to C# and coding in general. I am trying to write a program that has some logic and that also indicates progress with a progressbar. I am starting a thread in Main() that does all my business logic. It has events that are trigerred at points that I need the progress bar udpated.
The Form object subscribes to the business logic events and has thread safe delegates that are invoked to update the progress bars and text labels.
My problem is that, as the Form is started in the main thread, I have to start the business logic thread before Application.Run(). When the first ProgressUpdate event is trigerred, the Form object still does not exist. I guess a hacky way is to add Thread.Sleep(100) in the second thread, but I don't like that. How do I get around this? Am I on a completely incorrect track? (Am I even making sense?)
Form1 theForm = new Form1();
CreateReport theCreateReport = new CreateReport();
Thread t = new Thread(new ThreadStart(theCreateReport.DoProcess));
t.IsBackground = true;
theForm.Subscribe(theCreateReport);
t.Start();
Application.Run(theForm);
theForm is the form. theCreateReport is where my business logic starts.
You want to use one or more BackgroundWorker objects instead of your business logic thread. This will manage the threading for you as well as giving you a way to provide progress feedback to the main thread.
Maybe you should start your business logic in OnLoad event?
The Form already exists after you invoke the constructor (on the very first line) - it's just not visible yet. So you don't need to worry, everything is initialized when you start the new thread.
In Main, just create the form and Application.Run it. In the Load event of the form, start your thread.
You don't really gain any advantage from doing things the way you're currently doing them. And as you've already found, it creates a timing/sequence problem.
The best way to fix problems is to not have them in the first place.
I would use BackgroundWorker and you can still use your events and delegates with it. This time round you will be wrapping up and firing Background Worker's "ProgressChanged" and "RunWorkerCompleted" events.
And you Form can listen to these events and update ProgressBar accordingly.
BWorker handles switching to GUI Thread and Exception Handling better.
You can initialize BackgroundWorker on Form Load.
I'm writing a simple data UI using standard .Net databinding to a typed DataSet from SQL Server.
I have a reload button which calls Fill on all of the DataAdapters to get new data from the database (in case another user changed the data).
This takes some time, during which the UI is frozen. It must be run on the UI thread or the databinding event handlers throw cross-thread exceptions.
I'd like to show a modal "Please Wait" dialog on a background thread (so that it can be animated) while the UI thread connects to the database.
How can I show a modal dialog box on the non-UI thread?
EDIT: I'm aware that best practice is to run the operation in the background, but I can't do that because of the databinding events.
You should do the opposite. Run your long-running process on a background thread and leave the UI thread free to respond to the user actions.
If you want to block any user actions while it is processing you have a number of options, including modal dialogs. Once the background thread completes processing you can inform the main thread about the outcome
The code running in the databinding events need to be decoupled from the UI, probably using some kind of data transfer object.
Then you can run the query operation in a separate thread or a BackgroundWorker, and leave the UI thread as it was.
Edit: The really quick way to fix this is to get the events to run in their own delegate using InvokeRequired and .Invoke. That will give the methods UI context. My co-worker does this like it's going out of style and it annoys me to no end because it's rarely a good idea to do it this way... but if you want a fast solution this will work. (I'm not at work so I don't have a sample with me; I'll try to come up with something.)
Edit 2: I'm not sure what you're asking for is possible. I made a sample app that created a modal dialog in another thread, and it ends up being modeless. Instead of using a modal dialog, could you use some other control or set of controls to indicate progress change, most likely directly on the same form?
using( var frmDialog = new MyPleasWaitDialog() ) {
// data loading is started after the form is shown
frmDialog.Load += (_sender, _e) {
// load data in separate thread
ThreadPool.QueueWorkItem( (_state)=> {
myAdapter.Fill( myDataSet );
// refresh UI components in correct (UI) thread
frmDialog.Invoke( (Action)myDataControl.Refresh );
// close dialog
frmDialog.Invoke( (Action)frmDialog.Close() );
}
}
// shows dialog
frmDialog.ShowDialog( this );
}
Here is an example of using BackgroundWorker to do the loading of data and running a user friendly form to show 'Loading records' or similar...
public void Run()
{
bgWorkrFillDS = new BackgroundWorker();
bgWorkrFillDS.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bgWorkrFillDS_RunWorkerCompleted);
bgWorkrFillDS.DoWork += new DoWorkEventHandler(bgWorkrFillDS_DoWork);
bgWorkrFillDS.RunWorkerAsync();
}
void bgWorkrFillDS_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker bgWrkrFillDS = (BackgroundWorker)sender as BackgroundWorker;
if (bgWrkrFillDS != null)
{
// Load up the form that shows a 'Loading....'
// Here we fill in the DS
// someDataSetAdapter.Fill(myDataSet);
}
}
void bgWorkrFillDS_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
// Hide or unload the form when the work is done
}
Hope this helps...
Take care,
Tom.
I solved this problem by creating a new DataSet, loading in in the background, then calling DataSet.Merge on the UI thread. Thanks everyone for your advice, which led to this solution.
As an added bonus, this runs much faster than it used to (calling Fill in the background, which only worked with no grids open). Does anyone know why?
I've got a Windows Forms (C#) project with multiple comboboxes/listboxes etc that are populated when the form loads.
The problem is that the loading of the comboboxes/listboxes is slow, and since the loading is done when the form is trying to display the entire form isn't shown until all the controls have been populated. This can in some circumstances be 20+ seconds.
Had there been a Form_finished_loaded type of event I could have put my code in there, but I can't find an event that is fired after the form is done drawing the basic controls.
I have one requirement though - the loading has to be done in the main thread (since I get the items from a non-threading friendly COM-application).
I have found one potential solution, but perhaps there is a better way?
I can create a System.Timer.Timer when creating the form, and have the first Tick be called about 1 second later, and then populate the lists from that tick. That gives the form enough time to be displayed before it starts filling the lists.
Does anyone have any other tips on how to delay the loading of the controls?
There is the Shown event that "occurs whenever the form is first displayed.". Also you may want to use the BeginUpdate and EndUpdate functions to make the populating of your combobox faster.
It has that certain smell of workaround, but this approach should fulfil your needs:
private bool _hasInitialized = false;
private void Form1_Shown(object sender, EventArgs e)
{
if (!_hasInitialized)
{
ThreadPool.QueueUserWorkItem(state =>
{
Thread.Sleep(200); // brief sleep to allow the main thread
// to paint the form nicely
this.Invoke((Action)delegate { LoadData(); });
});
}
}
private void LoadData()
{
// do the data loading
_hasInitialized = true;
}
What it does is that it reacts when the form is shown, checks if it has already been initialized before, and if not it spawns a thread that will wait for a brief moment before calling the LoadData method on the main thread. This will allow for the form to get painted properly. The samething could perhaps be achieve by simply calling this.Refresh() but I like the idea of letting the system decide how to do the work.
I would still try to push the data loading onto a worker thread, invoking back on the main thread for populating the UI (if it is at all possible with the COM component).
Can you get your data from a web service that calls the COM component?
That way, you can display empty controls on a Locked form at the start, make Asynchronous calls to get the data, and on return populate the respective combos, and once all of them are loaded, you can unlock the form for the user to use.
You could listen for the VisibleChanged event and the first time it's value is true you put your initialization code.
Isn't FormShown the event you're looking for?
When you say that you cannot use a background thread because of COM what do you mean? I am using many COM components within my apps and running them on background threads.
If you create a new thread as an STAThread you can probably load the ComboBox/ListBox on a Non-UI thread. IIRC the ThreadPool allocates worker threads as MTAThread so you'll need to actually create a thread manually instead of using ThreadPool.QueueUserWorkItem.