Sample Code for a GUI Delphi Application With Multiple Threads.Zarko Gajic is experienced in SQL and has working knowledge of DB systems such as MS SQL Server, Firebird, Interbase, and Oracle.A normal Delphi application is single-threaded, which means all VCL objects access their properties and execute their methods within this single thread.To speed up data processing in your application, include one or more secondary threads.
Single-threaded programs need communication to flow in both directions (to and from the processor) as it executes; multi-threaded apps can open several different channels, thus speeding up execution. Image Listview Delphi Runtime From Database Update Your GraphicalWhen several threads are running in the application, the question arises of how you can update your graphical user interface as a result of a thread execution. To update your applications user interface, or main thread, from a secondary thread, you need to call the Synchronize method. This technique is a thread-safe method that avoids multi-threading conflicts that can arise from accessing object properties or methods that are not thread-safe, or using resources not in the main thread of execution. Below is an example demo that uses several buttons with progress bars, each progress bar displaying the current state of the thread execution. ThoughtCo, Aug. 25, 2020, thoughtco.comsynchronizing-threads-and-gui-delphi-application-1058159. Image Listview Delphi Runtime From Database Code Of TheAs previously mentioned, the sorting support was already there, which could have saved most of the code of the example. The standard list box and combo box components are very common, but they are often replaced by the more powerful ListView and TreeView controls. These two controls are part of the Win32 common controls, stored in the ComCtl32.DLL library. Similar controls are available in Qt and VisualCLX, both on Windows and Linux. In the RefList example, Ive set the first two properties using two different ImageList components. For this technique to work properly, the elements in the two image lists should follow the same order. When you have a fixed image list, you can add items to it using Delphis ListView Item Editor, which is connected to the Items property. In this editor, you can define items and subitems. The subitems are displayed only in the detailed view (when you set the vsReport value of the ViewStyle property) and are connected with the titles set in the Columns property. In Qt, this type of display is available from another component, the IconView. Saving and loading the contents of a ListView is not trivial, because the TListItems type doesnt have an automatic mechanism to save the data. As an alternative approach, Ive copied the data to and from a string list, using a custom format. The string list can then be saved to a file and reloaded with a single command. For each list item, the program saves the caption on one line, the image index on another line (prefixed by the character), and the subitems on the following lines, indented with a tab character. You can see some combinations of these styles in Figure 5.12. First, you set the SortType property of the ListView to stBoth or stData. Each time a column is clicked, the program saves the number of that column in the form classs nSortCol private field. The control is already capable of sorting itself properly when its caption is clicked. You automatically get multiple columns that auto-sort (both ascending and descending). When the user left-clicks an item, the RefList program shows a description of the selected item. Right-clicking the selected item sets it in edit mode, and a user can change it (keep in mind that the changes will automatically be saved when the program terminates). Here is the code for both operations, in the OnMouseDown event handler of the ListView control. Ive also activated the hot-tracking feature, which lets the list view highlight and underline the item under the mouse. The relevant properties of the ListView can be seen in its textual description. Large and small icons are available in a different control, called IconView.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |