TdxForm Class
The base class for DPI-aware DevExpress application forms.
Declaration
TdxForm = class(
TForm,
IdxScaleFactor,
IdxAutomationElement
)
Remarks
The TdxForm
class is designed to substitute TForm as a form ancestor in DPI-aware applications. An instance of a form class derived from TdxForm
(TdxRibbonForm, for instance) automatically updates its scale factor and applies it to all DevExpress controls when your application accepts the WM_DPICHANGED
[1] system message.
Tip
Different supported Embarcadero RAD Studio® IDE versions have different DPI awareness implementations. To ensure the best experience with DevExpress components in multi-monitor mixed-DPI environments regardless of the RAD Studio version, we recommend that you derive all forms in your application project from TdxForm
and its descendants.
Form Creation: Derive a DPI-Aware Form from TdxForm
To use the TdxForm
class as a direct ancestor class for a form in your application, you need to create a new form in the RAD Studio IDE, add the dxForms unit to the uses clause, and replace TForm with TdxForm
in the form class declaration as follows:
uses dxForms; // This unit declares the TdxForm class
// ...
type
TMyForm = class(TdxForm)
private
{ Private declarations }
public
{ Public declarations }
end;
Main API Members
The list below outlines key members of the TdxForm
class that allow you to configure a DPI-aware application form.
General Form Settings and Methods
The following public API members are derived from the standard TForm class shipped with the VCL library:
- Caption
- Specifies the form’s caption.
- PixelsPerInch
- Specifies the base DPI value for scale factor calculations.
- ShowModal
- Invokes the form as a modal dialog.
- Scaled
- Specifies if DPI awareness is enabled for the form.
- Visible | Hide | Show
- Hide or display the form.
- Width | Height | ClientWidth | ClientHeight
- Allow you to adjust form and client area dimensions.
Tip
Refer to the TForm class description for detailed information on all standard form API members.
DPI Awareness Implementation
The following API members implement DPI awareness for DevExpress forms regardless of the target Embarcadero RAD Studio® version. You do not need to interact with these API members in your code in the majority of usage scenarios. However, you can override certain methods in custom TdxCustomForm
class descendants to change predefined form responses to monitor DPI changes.
- ChangeScale
- Multiplies the form’s scale factor by the specified scale factor.
- ScaleBy
- Updates the form’s scale factor.
- ScaleFactor
Returns the form’s scale factor that updates every time your application accepts the
WM_DPICHANGED
system message if the Scaled property is set toTrue
.You can use this property to identify the current scale factor or call any of the ScaleFactor.Apply functions to apply the scale factor to custom-drawn UI elements within the form.[1]
- ScaleForPPI
- Scales the form and components within it according to the specified target DPI.
- ScaleFactorChanged
Automatically scales the form when its scale factor changes.
You can override[2] this procedure in custom
TdxForm
class descendants to execute custom code when the monitor DPI changes.- UpdateImageLists
Automatically switches between DPI-aware image lists whose stored bitmaps target different monitor DPIs if the dxAutoReplaceImageListReferencesOnDPIChanges global variable is set to
True
.You can override this procedure in custom
TdxForm
class descendants to implement different image list replacement criteria.Tip
We recommend that you use only SVG images in all projects that target multi-monitor and high-DPI environments.
Other DPI-Aware Form Classes
DevExpress VCL products ship with the following base form classes with support for DPI-awareness:
- TdxAlertWindow
- An alert window.
- TdxRibbonForm
- A Ribbon form class.
- TdxFluentDesignForm
- A Fluent Design application form.
- TdxSkinForm
- The base class for simple DPI-aware forms that can override global form corner and shadow settings.
Additional Information
Refer to the following help topic for detailed information on how to adapt your application to high-DPI environments: High DPI and Graphics.