I have a tax calculator, with 1 input and 2 results in textboxes. User inputs amount, result 1 will show Result2 - Input and result 2 will just show the calculation done in Button.Click.
How do I make it so that it auto changes the results in the 2 textboxes on every keystroke with the input Textbox? I tried to use sendkeys Enter on textbox.change but WPF doesn't have sendkeys. Please help!
Rather than repeat all of the details of an answer I provided to another SO user I'll just put a link to it here.
If you were to use that logic then you could pick up the textbox's TextChanging event use that to carry out your logic and presumably update the properties to which your other text boxes are data bound thus automatically updating them as you require.
There is an assumption here on my part that you are using mvvm. If you aren't then what you want to achieve should be pretty straightforward in the code behind so long as you have remembered to name everything.
Related
I have read all sorts of documents across the web about what should be a farly common and painless implementation. Since I have found no consistent and slick reply (even the Embarcadero website describes some properties wrong!) I am going to post a "short" howto.
Typical, frequent use case: the developer just wants to painlessy show a couple of database-extracted information in a combo box (i.e. a language selection), get the user's choice out of it and that's it.
Requirements:
Delphi, more or less any version. VCL is covered.
A database table. Let's assume a simple table with an id and value fields.
A DataSet (including queries and ClientDataSets).
A DataSource linked to the DataSet.
A TDBLookupComboBox linked to the DataSource that shall show a list of values and "return" the currently selected id.
Firstly, we decide whether the sort order is the one we want or not and if all the items in that table must be shown. Most often, a simple ORDER BY clause or a DataSet index will be enough. In case it's not, we may add a sort_order field and fill it with integers representing our custom sort order. In case we want to show just some items, we add a visible or enabled field and use it in our SQL. Example:
SELECT id, value
FROM my_database_table
WHERE visible = 1
ORDER BY sort_order
I have defined visible as INTEGER and checking it against 1 and not TRUE because many databases (including the most used SQLite) have little support for booleans.
Then an optional but surprisingly often nice idea: temporarily add a TDBGrid on the form, link it to the same TDataSource of the TLookupComboBox and check that you actually see the wanted data populate it. In fact it's easy to typo something in a query (assuming you are using a SQL DataSet) and get no data and then you are left wondering why the TDBLookupComboBox won't fill in.
Once seen the data correctly show up, remove the grid.
Another sensible idea is to use ClientDataSets for these kinds of implementations: due to how they work, they will "cache" the few rows contained in your look ups at program startup and then no further database access (and slowdown and traffic) will be required.
Now open the TDBLookupComboBox properties and fill in only the following ones:
ListSource (and not DataSource): set it to the TDataSource connected to the DataSet you want to show values of.
ListField: set it to the field name that you want the user to see. In our demo's case it'd be the value field.
KeyField: set it to the field name whose value you want the program to return you. In our demo it'd be the id field.
Don't forget to check the TabOrder property, there are still people who love navigating through the controls by pressing the TAB key and nothing is more annoying than seeing the selection hopping around randomly as your ComboBox was placed last on the form despite graphically showing second!
If all you need is to show a form and read the TDBLookupComboBox selected value when the user presses a button, you are pretty much sorted.
All you'll have to do in the button's OnClick event handler will be to read the combo box value with this code:
SelectedId := MyCombo.KeyValue;
Where SelectedId is any variable where to store the returned value and MyCombo of course is the name of your TDBLookupComboBox. Notice how KeyValue will not contain the text the user sees onscreen but the value of the id field we specified in KeyField. So, if our user selected database row was:
id= 5
value= 'MyText'
MyCombo.KeyValue shall contain 5.
But what if you need to dynamically update stuff on the form, depending un the combo box user selection? There's no OnChange event available for our TDBLookupComboBox! Therefore, if you need to dynamically update stuff around basing on the combo box choices, you apparently cannot. You may try the various "OnExit" etc. events but all of them have serious drawbacks or side effects.
One possible solution is to create a new component inheriting from TDBLookupComboBox whose only task is to make public the hidden OnChange event. But that's overkill, isn't it?
There's another way: go to the DataSet your TDBLookupComboBox is tied to (through a DataSource). Open its events and double click on its OnAfterScroll event.
In there you may simulate an OnChange event pretty well.
For the sake of demonstration, add one integer variable and a TEdit box to the form and call them: SelectedId and EditValue.
procedure TMyForm.MyDataSetAfterScroll(DataSet: TDataSet);
var
SelectedId : integer;
begin
SelectedId := MyDataSet.FieldByName('id').AsInteger;
EditValue.Text := MyDataSet.FieldByName('value').AsString;
end;
That's it: you may replace those two demo lines with your own procedure calls and whatever else you might need to dynamically update your form basing on the user's choices in your combo box.
A little warning: using the DataSet OnAfterScroll has one drawback as well: the event is called more often than you'd think. In example, it may be called when the dataset is opened but also be called more than once during records navigation. Therefore your code must deal with being called more frequently than needed.
At this point you might rub your hands and think your job is done!
Not at all! Just create a short demo application implementing all the above and you'll notice it lacks of an important finishing touch: when it starts, the combo box has an annoying "blank" default choice. That is, even if your database holds say 4 choices, the form with show an empty combo box selected value at first.
How to make one of your choices automatically appear "pre-selected" in the combo box as you and your users expect to?
Simple!
Just assign a value to the KeyValue property we already described above.
That is, on the OnFormCreate or other suitable event, just hard-code a choice like in example:
MyCombo.KeyValue := DefaultId;
For example, by using the sample database row posted above, you'd write:
MyCombo.KeyValue := 5;
and the combo box will display: "MyText" as pre-selected option when the user opens its form.
Of course you may prefer more elegant and involved ways to set a default key than hard-coding its default value. In example you might want to show the first alphabetically ordered textual description contained in your database table or whatever other criterium. But the basic mechanic is the one shown above: obtain the key / id value in any manner you want and then assign it to the KeyValue property.
Thank your for reading this HowTo till the end!
I have bunch of textboxes bound to a datagridview. I want to prevent users from leaving a row if invalid input is entered.
I tried both the RowLeave and RowValidating events. They both give me the data row user is entering, not the old one. Therefore, in the RowValidating events, when I set the event.cancel=true, it does not revert back to the old row.
Basically I need a way to capture the row the user is trying to leave, and I am not able to do it with any of the those events.
Thanks!!
Edit : I guess a silly way to do it is via rowEnter event. I imagine I can accomplish what I want with that, but all the purpose of those fancy events are lost...
Update : I think the problem is with the data binding. I can see the underlying datarow is locked but that is not reflected in the textboxes. Yikes..
Try CellValidating, I know this used to work for me.
I have a following requirement for a very complex UI. (Complex here means there are lot of controls in the form [approximately 100]). I am using MVVM (if my problem requires it to slightly go away from MVVM I am ok with it)
My question is for Editable ComboBox and TextBox. But I would say I like to hear a common algorithm which will fit all controls.
Requirement 1 : The user edits the content and goes to next control, the color of the control/text should become red.
Requirement 2 : When the user comes back to the previously edited control and enters the value which was initially present, the color of the control/text should become back to black.
I know the requirement is tough and I have been breaking my head to design a generic algorithm using which I can store the previous value and call a function to change the color of control.
To just give you all an idea, --> I tried storing 2 properties for every TextBox like Default_Text and Text. But since the number of properties are huge, the memory footprint is very huge. Also maintaining so many properties is very tough.
--> I tried adding a Dictionary to every ViewModel to store what values have got changed. But here the problem I faced was giving unique keys to all the controls in my application, which is not very helpful
--> I had even thought and tried about subclassing controls like TextBox, ComboBox and overriding some methods to suit my requirement, but sadly I failed miserabley when I started adding validations and all.
So here I am stuck with designing a generic WPF property system/algorithm to handle all undo redo functionality, changing styles of controls,etc!!!
It will be really great if you experts can guide me in right direction and also help me in developing such an algorithm/system. A sample illustration will be nice though!!!
I found an answer to the above problem. I used attached behavior for this. More details on this link Function call from XAML from StackOverFlow.
When I databind, I store the initial value of the DataBound variable in the Tag property by using Binding=OneWay. Then I have written a attached behaviour for LostFocus event. Whenever the user enters a control and then goes to other control, it fires LostFocus event and calls my attached behaviour. In this, I check whether the value is equal to the value in Tag. If it is same, I display in black else I display in red.
Attached Behaviour rocks in WPF. I can achieve anything from that cleanly without code cluttering!!!!
Another alternative is to use some "dirty" tracking in your models (or viewmodels) and bind to a properties isdirty (and convert it to a color).
Suppose I have a Window with TextBoxes I want to use the values. Right now I'm thinking of either:
1) Updating each associated value once the cursor is out of focus, and once the user presses Ok I start the program
2) Once the user presses Ok, I retrieve all the values at once then start the program
I'm not sure which one is better though. First alternative seems more modular, but there's more semantic coupling since I each new box is supposed to be updating its respective value.
I realize this isn't all that important, but I'm trying to understand when to centralize and when not to. Other better approachers are appreciated too.
Use data binding to bind the text boxes' contents to objects in your code behind. WPF will take care of updating your attributes. Usually updating the data-bound value is done when the focus is lost on text boxes. However, you can also specify that it will happen whenever the value changes.
When editing text the user is able to use the keybord shift button and direction keys to modify the selection - one position stays anchored while the other moves. By pressing left it is possible to get the movable part on the left of the anchored part.
I'm trying to dinamicaly modify the users selection in WPF's TextBox (for the purpose of the discussion, lets say I want to select the characters in pairs, eg. when pressing shift+left, 2 characters would get selected, not just one). However, when using SelectionStart/SelectionIndex/CaretIndex/Select the "movebale end" of the selection is always ends up on the far right end of the selection, rendering the shift+left combination useless.
Any way to preserve the "selection direction"?
This is not quite the answer you are looking for but it'll work. Invoke the command and do it the way WPF does it.
EditingCommands.SelectLeftByCharacter.Execute(null, textBox1);
None of those work. SelectionLength doesn't allowed to be negative, and CaretIndex is always identical to SelectionStart. This is a design bug in TB, as you cannot achieve a valid state of it even in the protected scope.
The command actually works, but you still cannot determine the selection's direction of the currently analyzed textbox. There's only one solution, which is an ugly workaround: You can write your own observer code by overriding the mouse and keyboard event handlers.
The only possibility I can think of is to set the SelectionStart and then make the SelectionLength negative.
Have you tried setting the CaretIndex property before or after setting SelectionStart/SelectionLength?