|
Switching tabs causes "user control loaded" to fire.
Other than that, if it's just "read only", I would've just "marked it up" and output that (instead of pretending grid "code behind" is "mvvm"; your "model" is bleeding into your "view".)
"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal
|
|
|
|
|
Hi everyone,
i need some help, doing a school work, i'm using a datagrid to display some info from my database.
<DataGrid x:Name="dataGridProduit" SelectionMode="Single" AutoGenerateColumns="false"
ItemsSource="{Binding MyProducts}"
SelectedItem="{Binding SelectedProduct, Mode=TwoWay}">
<DataGridTextColumn x:Name="Nom" Header="Nom" Binding="{Binding Name, Mode=TwoWay}" Width="*"/>
Then textbox filled with info from selectedItem
<TextBox x:Name="tbName" Height="23" Text="{Binding SelectedProduct.Name, Mode=TwoWay}"
works fine for remove,update.
But now, i'd like to add new product this way :
<Button x:Name="buttonAdd" Style="{DynamicResource ButtonStyleMainWindow}" Command="{Binding AddCommand}" CommandParameter="{Binding SelectedProduct}" />
The problem is clear, it adds but also update my selectedProduct. What would be the best solution here? other issue is, if i just fill the textboxes, then i don't raise a selectedProduct to viewmodel and then my object is null :/
i'm working now on alternative way and opening new window to add user but really i'm blind on the best way to do this
so thank u for any help u can give to me 
modified 6-Sep-18 10:01am.
|
|
|
|
|
miniboom wrote: i'm working now on alternative way and opening new window to add user
This is the way I do all data entry. Pop a modal dialog and allow the user to manage 1 record (SelectedProduct), save the record and update the collection.
As for your button command you do not want a SelectedProduct as the first thing you will do in the Add method is to create a new product.
I would do the following in your Add method:
Create SelectedProduct = new Product
Call the ShowDialogMethod
In your UpdateMethod
Call the ShowDialogMethod
ShowDialogMethod should
Instantiate the modal dialog (dialog view to reference the SelectedProduct)
Show the dialog
SaveDialog
Update the database
Either Add the new record to your product collection or update the SelectedProduct with the results of the database save.
There are a number of pitfalls depending on your DAL but once you have this methodology down pat it works for ALL your data entry needs.
I almost never use inline (in grid) editing, always pop a dialog it gives you dramatically more control of your record.
For simple data entry I used the same VM as the list. If the dialog is complex I will use a separate VM for it.
Never underestimate the power of human stupidity
RAH
|
|
|
|
|
thank you very much for all these advice I already succeed in adding new product with modaldialog but it seems tricky to do the same for update at least for now. Didn't do it with Mvvm but a simple event to open the dialog in code behind :
private void button1_Click(object sender, System.Windows.RoutedEventArgs e)
{
var window = new AddProductWindow { DataContext = this.DataContext };
window.ShowDialog();
}
i'm using entity framework btw
|
|
|
|
|
miniboom wrote: i'm using entity framework
Most beginners and junior devs use EF, most senior and enterprise devs build their own DAL. I have a negative opinion of EF  .
Never underestimate the power of human stupidity
RAH
|
|
|
|
|
This is in a Class called ST:
public Class ST
{
private readonly System.Timers.Timer _timer;
private DateTime _lastScanTime;
public ST()
{
_timer = new System.Timers.Timer();
_timer.Interval = 250;
_timer.Start();
_timer.Elapsed += OnTimerElapsed;
}
public TimeSpan ScanTime { get; private set; }
private void OnTimerElapsed(object sender, ElapsedEventArgs e)
{
try
{
_timer.Stop();
ScanTime = DateTime.Now - _lastScanTime;
OnValuesRefreshed();
}
finally
{
_timer.Start();
}
_lastScanTime = DateTime.Now;
}
private void OnValuesRefreshed()
{
ValuesRefreshed?.Invoke(this, new EventArgs());
}
}
Then a value of Scantime is being transferred via MVVM pattern (ViewModel) to UI.
The major question is what do we really have valuable when we do a substraction as follows: ScanTime = DateTime.Now - _lastScanTime? This point I can't figure out.
Thanks in advance!
|
|
|
|
|
This code would be called in a loop structure. First time it is called _LastScanTime is populated and the ScanTime is irrelevant. All subsequent calls update the ScanTime using subtraction and the _LastScanTime with the current time.
I suggest you get a book (or many books) and work through the examples if this simple logic baffles you.
Never underestimate the power of human stupidity
RAH
|
|
|
|
|
@Holmes, my dear,
oddly enough, I knew a structure of this code, like nobody's business. I asked a bit a different stuff.
Let me repeat that: I wish I knew what we really have useful by substraction as follows: ScanTime = DateTime.Now - _lastScanTime?? When the code is running I have a quickly alterating value 250-270 ms.
P.S. Next time, before replying, just try to read posts more carefully. As concerned books, please do me a favour, show me a book where is written for what it is being done by mentioned substraction. I'll be waiting for such useful book.
Pew
modified 5-Sep-18 1:02am.
|
|
|
|
|
So you have a ScanTime of 250-270ms.
It is generated by subtracting the current time (DateTime.Now) from the _LastScanTime which was populated by the last loop. It represents the number of milliseconds the system takes to complete the processing loop from the VM.
PS It is still a very straight forward piece of code which is staggeringly simple. Try adding
Thread.Sleep(100) after your subtraction line and see what happens.
Never underestimate the power of human stupidity
RAH
|
|
|
|
|
Holmes> It represents the number of milliseconds the system takes to complete the processing loop from the VM.
I was waiting for this sentence.
For what this stands for? I mean, e.g. a label with mentioned milliseconds inside, on UI screen.
Just show to UI user that app is alive?
modified 5-Sep-18 4:36am.
|
|
|
|
|
Pew_new wrote: The major question is what do we really have valuable when we do a substraction as follows: ScanTime = DateTime.Now - _lastScanTime?
I cannot see anything 'valuable' in this. It merely gives you the actual elapsed time between the timer start and the first tick. Since your timer interval is set at 250 (milliseconds) it should be somewhere around that value. The question really is what this code is being used for?
|
|
|
|
|
Richard MacCutchan> The question really is what this code is being used for?
I would ask you this way.
My guess is it provides an UI user some kind of "Warning". Something like "Your PC's processor is so busy that the ScanTime went out of allowed time range." Of course in case when value is out of tolerance "window". A value is out of tolerancee "window" - text of value is highlighted with red.
modified 5-Sep-18 4:40am.
|
|
|
|
|
So why exactly are you asking here? We have no information on the context that this code runs inside, or what the application is trying to do.
|
|
|
|
|
Some info I gave in the first post:
Timer -> Timer procedure and calculation -> MVVM pattern -> UI.
As said Mr.Holmes. It's very simple code.
modified 5-Sep-18 5:08am.
|
|
|
|
|
Which means absolutely nothing. I still do not understand exactly what you are asking.
|
|
|
|
|
It may close this topic. I've got comrehensive answer from Mr.Holmes.
If you're interested in. This is answer: It represents the number of milliseconds the system takes to complete the processing loop from the VM.
|
|
|
|
|
No, it is just the number of milliseconds between the timer starting, and the Elapsed event being fired. This will occur after approximately 250 milliseconds as declared by the timer intialisation values.
|
|
|
|
|
Richard MacCutchan wrote: This will occur after approximately 250 milliseconds as declared by the timer intialisation values.
Ah crap I completely missed that, even after rereading the dammed code.
Never underestimate the power of human stupidity
RAH
|
|
|
|
|
We've all done that from time to time. Although, I was actually worried that I was missing something that you had noticed.
|
|
|
|
|
There appear to be a couple of structural issues with this code. The first thing is, you haven't shown us the complete class. Secondly, you update _lastScanTime to a different DateTime.Now than when you update ScanTime - in a multi-threaded application, this could be a potentially significant difference because of your ValuesRefreshed. To be honest, I don't know why you don't make ScanTime raise INotifyPropertyChanged.PropertyChanged and avoid other events; you can bind directly to that value. Also, I would use a StopWatch instead of DateTime.Now if I were you.
This space for rent
|
|
|
|
|
|
Yes. It's not going to be trivial though.
This space for rent
|
|
|
|
|
Hello everyone.
Currently I am trying to work with timers in WPF.
private void Window_Loaded(object sender, RoutedEventArgs e)
{
_timer = new System.Timers.Timer();
_timer.Interval = 1000;
_timer.Elapsed += OnTimerElapsed;
_timer.Start();
}
int i=0;
private void OnTimerElapsed(object sender, ElapsedEventArgs e)
{
i++;
label1.Content = i.ToString();
}
I've got an exception at this string
label1.Content = i.ToString();
What I'm doing wrong with a label?
Thanks in advance!
XAML:
<Label x:Name="label1" HorizontalAlignment="Center" Margin="2" VerticalAlignment="Center" Height="79" Width="86"/>
modified 3-Sep-18 4:19am.
|
|
|
|
|
Pew_new wrote: What I'm doing wrong with a label?
You access it from a different thread - you must not do that, and that holds true also for other UI technologies like WinForms.
With WPF also comes MVVM. Instead of setting the Content property directly, you bind it to some property of your view model. When that property changes, you raise an PropertyChanged event, and that will do the magic of "transporting" the change in the correct thread.
Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!
|
|
|
|
|
Please explain where have you seen " different thread"?
"different thread", you mean that with a System.Timer it's not possible?
P.S. Here https://www.youtube.com/watch?v=QkT8fgoFz3g, a guy is doing that easily. True he's using a Dispatcher Timer. So what's difference?
modified 3-Sep-18 5:17am.
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
