So I'm messing around with a new project in Delphi 2009 and the default components that can be dropped onto a form for accessing data consist of a SQLConnection, DataSource and SQLQuery. If I add a simple select to the query component, say:
select name from customers
and then drop a DBComboBox on the form and link it up with the DataSource I get a single record in the combo box. After using Google for half and hour to figure out what I was doing wrong it looks like you have to manually add some code to your project which loops through the dataset and adds all the records to the drop down box. Something like:
while not SQLQuery.eof do
begin
DBComboBox.items.add(SQLQuery.fieldbyname('name').asstring);
SQLQuery.next;
end;
And that actually sort of works, but then you get a list in the drop down which you can't actually select anything from. Regardless of the result though I'm wondering why would you even use a DBComboBox if you have to manually add the result of your query to it? Seems to me that if it doesn't automatically populate the db combo box with the result of the query then we might as well be using a non-data-aware component like tcombobox.
I guess what I'm asking is why does it work this way? Isn't the purpose of data aware drag-and-drop controls to minimize the amount of actual written code and speed development? Is there a method that I'm missing that is supposed to make this easier?
A TDBComboBox doesn't get its list of values from the database; it gets its current value from the database. Link it to a field in your dataset, and when you change the active record, the combo box's current value will change. Change the combo box's current value, and the corresponding field's value will change.
If you want to get the list of values from the database as well, then use a TDBLookupComboBox.
This is all covered in the help:
Using TDBListBox and TDBComboBox
Displaying and Editing Data in Lookup List and Combo Boxes
Defining a Lookup List Column
I think you want the TDBLookupComboBox because that allows you to lookup from a list of items where the list comes from a dataset.
In the TDBComboBox, the list is just a TStrings manually filled with data.
--jeroen
DbCombox is a dbaware version of the standard combobox component.
Related
I have an application that will load a CSV file containing two columns. At program load I need to have the first column as items in a combo edit control. Once the user selects (or enters a value) I need to populate a label with the value from the second column. My thought was to use an in memory data set, FDMemTable which would be loaded at form create. Then once the user selects, or enters an item, I would run a query to pull the description. I've tried but have been unsuccessful with the simple loading of the combo edit.
Is this the best way to achieve the desired results, and is there samples similar to what I'm looking to do?
Read the file.
Parse it into an array of name/value pairs.
Populate the combo drop down list with the names.
When the combo's selection is changed to a new index, read the value from the array using that index. Update the label.
Database tables and queries seem somewhat over the top for a single simple task like this.
am using a VCL form in Delphi, where I have put about 10 edit boxes.
These Edit boxes contain values that are related to specific models of solar panels.
These values are needed in order to calculate the output power of a solar panel.
So far, I am able to type these values in every run with the command:
c0:= StrToFloat(Edit1.Text);
for c0 to c10. But, instead of asking the user to manually type these 10 values in each run, is there any way to let the user select one option (i.e. a model of a solar panel) of a drop down list and these values being filled automatically for them?
Does the combobox do such a thing and if yes, how exactly? I am sorry, I am a very new Delphi user. Any help much appreciated.
Set the combo box Style to csDropDownList.
Populate the combo box Items with appropriate values for the user to select.
Add an OnSelect event handler. This will fire whenever the user selects a new item in the combo box.
Implement the OnSelect event handler by populating the edit controls with appropriate values, based on the value of ItemIndex.
You will need to think a little about the UI. If the user changes the combo box selection, then the edit control values change. But can the user then modify the edit controls? Now the values in the edit controls no longer match the combo box. Is that what you want? I guess that the UI needs a little more polish.
I'm new to delphi and have created an SQL query which displays the results of a search entered by the user through an edit box (showing data from 2 related tables) in a dbGrid.
The dbgrid displays no data until a search has been made and then the results of that search are displayed, however i was wondering whether it was possible to show all the related data in the dbgrid as if it were a table and the search then simply selects from it?
thanks
You could display all the data in the table. Then write an onExit event handler for your edit box which would look something like this (assuming that the string which you are entering in the edit box is supposed to match the value in the 'name' field of the query)
query.locate ('name', edit1.text, [loPartialValue]);
This will cause the dbgrid's cursor to jump to the first line which matches the string in the edit box.
Instead of using the OnExit event, you could also use the OnChange event of the edit box, but this would mean a search after every key stroke.
Your question was a bit vague so it's difficult to give a specific answer.
I am trying to create a Delphi grid to allow display and edit in a db grid of data that might have a different data type on each row. I would like to display a specific control for each data type, e.g. when the data type is DateTime, I want to display my custom edit control that allows typing a date in or popping up a calendar.
The data looks something like this:
Name DataType DateValue StringValue BooleanValue
---------------------------------------------------------
A Date 1/1/2007
B String asdf
C Boolean True
...and in the db, this table has a column for each possible type of value. So, there is a BooleanValue column, DateValue, etc.
What I would like to do is display a single 'Value' column in the grid that displays the appropriate edit control depending on what the 'DataType' is for that row. So, the grid should look like :
Name DataType Value
---------------------------
A Date 1/1/2007
B String asdf
C Boolean True
It seems I will need to display a different edit control (to allow the user to edit the Value column) for each row dynamically based on the value of the DataType column. I know there are more advanced grids out there that handle this sort of problem, but the powers that be will not allow anything but what is available out-of-the-box with Delphi.
Any ideas on how to make something like this work?
Personally, I would not go for editing directly inside the TDBGrid in this case, since your Table is not DB normalized (I don't use it in any case actually). I would have used a Calculated field to display the desired value in the grid, And dynamically created the TDBxxxEdits on the form for each field type (How about your own TDBTreeEdit for example, a TDBRichEdit, or a DB Image pickup editor, etc...?).
In case you do want to use your own controls on the TDBGrid, and replace the default TInplaceEdit editor, you can refer the following article: Adding components to a DBGrid, and a related article: Displaying and editing MEMO fiels in Delphi's TDBGrid
Displaying all of the data in the same column is quite easy. You can simply add a calculated string field, and change the value according to what you are storing in that row.
The editing is quite a bit more complicated. If you want to have an in-place editor, you are in for a world of hurt... I've done it, it's a pain, and takes a lot of time. If you want to display a dialog to edit the value, that's much easier. You can add a column objects to the grid and you can setup the column you have attached to the calc field to display a button. When the button is clicked you simply display the editing dialog needed for that row, and commit the edits when the dialog is closed.
There are other ways to get this done, but I would say the above would be the shortest way. Other ways may include custom draw events to display your data in one column, intercept clicks to create your own editor, etc, etc, etc...
after add calculated fields .
Sample:
procedure OnCalculate(DataSet:TDataSet);
begin
case IndexText(DataSet['ValueType'],['Date','String','Boolean']) of
0:DataSet['DateValue']:=StrToDateTime(DataSet['Value']); // also converting
1:DataSet['StringValue']:=DataSet['Value'];
2:DataSet['BooleanValue']:= MatchText(DataSet['Value'],['1','True','T','Y','Yes']);
{etc datatypes}
end;
end;
I have a SharePoint feature which programatically creates 3 lookups in a custom list, one from each of 3 different lists via extremely similar CAML markup.
The only differences in the CAML are the List, ID, Name, DisplayName and StaticName properties yet one of these lookups looks slightly different (has a slightly more "modern" drop-down arrow) than the other two and this same menu requires I double-click in order to select an item instead of single-clicking as I do with the other lookups.
Might anyone have seen this before and have an idea of what I might look into to make this lookup operate as a single-click menu?
The style of dropdown displayed is usually related to the number of items, although it also renders as a standard select element when viewed in firefox.
For any other field type it would make sense to create a custom field control, but due to code that expects things to be named "Lookup", lookup fields are next to impossible to extend.
The best way to customize a specific field is probably with javascript/jquery. When you click on the dropdown arrow, ShowDropdown (in core.js) is called. This creates a select element with options set from the pipe delimited list in the choices attribute of the textbox.
Add some code to the page so that on load EnsureSelect and FilterChoice or similar are called to create the select element. Set properties on the textbox and select elements so that the textbox as hidden and the select element is a visible dropdown. Have SetCtrlFromOpt called on change rather than on blur/double click so that the control that the server will read and save is properly updated.
The same approach could be used to keep the combo box but add a click event to set the value rather than requiring a double click.
How many items has the source list of every lookup field?
Lookup fields shows a "Combo" when the source list has 10 items (I'm not sure if 10 item is the exact limit). When the source list has more than 10 items the lookup field shows a "ListArea" control that works as you said.
I have exactly the same problem. One difference I have noticed is that the one listbox that requires a double-click is a lookup field, whereas the one that doesn't is a choice field with pre-populated choices. Don't know if that helps.