# Difference between revisions of "Dark theme"

How to detect whether the operating system is using a dark theme?

## Universal method

### Example 1

```// by "Alextp" from Lazarus forum
function IsDarkTheme: boolean;
const
cMax = \$A0;
var
N: TColor;
begin
N:= ColorToRGB(clWindow);
Result:= (Red(N)<cMax) and (Green(N)<cMax) and (Blue(N)<cMax);
end;
```

### Example 2

```// by "dbannon" from Lazarus forum
function IsDarkTheme(F: TForm): boolean;
var
Col : string;
begin
// if char 3, 5 and 7 are all 'A' or above, we are not in a DarkTheme
Col := HexStr(qword(F.GetRGBColorResolvingParent()), 8);
Result := (Col[3] < 'A') and (Col[5] < 'A') and (Col[7] < 'A');
end;
```

### Example 3

```// by "Hansaplast" from Lazarus forum
function _ColorToGrayScale(aColor:TColor):TColor;
var
GreyNumber: integer;
begin
Result:= ColorToRGB(aColor);
// Convert Color to Grayscale if not yet Grayscale
// Grayscale   = (0.3 * Red) + (0.59 * Green) + (0.11 * Blue)
// Alternative = (0.2126 * Red) + (0.7152 * Green) + (0.0722 * Blue)
if (Red(Result)<>Green(Result)) and (Red(Result)<>Blue(Result)) then
begin
GreyNumber:= ( ( MathRound(Red(Result)   * 0.3) +
MathRound(Green(Result) * 0.59) +
MathRound(Blue(Result)  * 0.11) )  div 3);

if GreyNumber<0 then
GreyNumber:=0
else if GreyNumber>255 then
GreyNumber:=255;

Result:= RGBToColor(GreyNumber,GreyNumber,GreyNumber);
end;
end;

function IsDarkTheme:boolean;
begin
Result := _ColorToGrayScale(clWindow) < _ColorToGrayScale(clWindowText);
end;
```

## Windows method

### Example 1

```// by "jwdietrich" from Lazarus forum
uses
Windows, Win32Proc, Registry;

// IsDarkTheme: Detects if the Dark Theme (true) has been enabled or not (false)
function IsDarkTheme: boolean;
const
KEYPATH = '\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize';
KEYNAME = 'AppsUseLightTheme';
var
LightKey: boolean;
Registry: TRegistry;
begin
Result := false;
Registry := TRegistry.Create;
try
Registry.RootKey := HKEY_CURRENT_USER;
begin
if Registry.ValueExists(KEYNAME) then
else
LightKey := true;
end
else
LightKey := true;
Result := not LightKey
finally
Registry.Free;
end;
end;
```

## macOS method

### Example 1

```// by "jwdietrich" from Lazarus forum
uses
MacOSAll;

function IsMinMacOS(Maj, Min: integer): boolean;
{ returns true, if this app runs on a macOS version as specified or newer }
var
Major, Minor: SInt32;
theError: SInt16;
begin
result := false;
theError := Gestalt(gestaltSystemVersionMajor, Major);
if theError = 0 then
theError := Gestalt(gestaltSystemVersionMinor, Minor);
if theError = 0 then
if (Major = Maj) and (Minor >= Min) or (Major > Maj) then
Result := True;
end;

{ returns true, if this app runs on macOS X 10.14 Mojave or newer }
begin
result := IsMinMacOS(10, 14);
end;

{ The following two functions were suggested by Hansaplast at https://forum.lazarus.freepascal.org/index.php/topic,43111.msg304366.html }

// Retrieve key's string value from user preferences. Result is encoded using NSStrToStr's default encoding.
function GetPrefString(const KeyName : string) : string;
begin
Result := NSStringToString(NSUserDefaults.standardUserDefaults.stringForKey(NSStr(@KeyName[1])));
end;

// IsDarkTheme: Detects if the Dark Theme (true) has been enabled or not (false)
function IsDarkTheme: boolean;
begin
Result := false;
Result := pos('DARK',UpperCase(GetPrefString('AppleInterfaceStyle'))) > 0;
end;
```

#### Demo

```unit Unit1;

{\$mode objfpc}{\$H+}
{\$modeswitch objectivec1}

interface

uses
Classes, Forms, Dialogs, StdCtrls, SysUtils,
CocoaAll, CocoaUtils, MacOSAll;

type

{ TForm1 }

TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private

public

end;

var
Form1: TForm1;

implementation

{\$R *.lfm}

{ TForm1 }

function IsMinMacOS(Maj, Min: integer): boolean;
{ returns true, if this app runs on a macOS version as specified or newer }
var
Major, Minor: SInt32;
theError: SInt16;
begin
result := false;
theError := Gestalt(gestaltSystemVersionMajor, Major);
if theError = 0 then
theError := Gestalt(gestaltSystemVersionMinor, Minor);
if theError = 0 then
if (Major = Maj) and (Minor >= Min) or (Major > Maj) then
Result := True;
end;

{ returns true, if this app runs on macOS X 10.14 Mojave or newer }
begin
result := IsMinMacOS(10, 14);
end;

function GetPrefString(const KeyName : string) : string;
begin
Result := NSStringToString(NSUserDefaults.standardUserDefaults.stringForKey(NSStr(@KeyName[1])));
end;

function IsDarkTheme: boolean;
begin
Result := false;
Result := pos('DARK',UpperCase(GetPrefString('AppleInterfaceStyle'))) > 0;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
if(IsDarkTheme) then
ShowMessage('Dark mode')
else
ShowMessage('Light mode');
end;

end.
```

### Example 2

Catalina added an "Auto" option where the computer switches between Light and Dark modes depending on time of day. The 'AppleInterfaceStyle' method apparently doesn't work if auto is enabled.

The solution is to get the NSApp.effectiveAppearance string which will be one of a number of values including 'NSAppearanceNameAqua' (standard light mode) and 'NSAppearanceNameDarkAqua' (standard dark mode). Google these to see the whole list which includes other light and dark modes with added contrast. The effectiveAppearance is correct in all modes including when auto mode kicks in.

Tested on Mojave, Catalina, Big Sur.

```// by "Clover" from Lazarus forum
function IsMacDarkMode: Boolean;
var
sMode: string;
begin
//sMode := CFStringToStr( CFStringRef( NSUserDefaults.StandardUserDefaults.stringForKey( NSSTR('AppleInterfaceStyle') ))); // Doesn't work in auto mode
sMode  := CFStringToStr( CFStringRef( NSApp.effectiveAppearance.name ));
Result := Pos('Dark', sMode) > 0;
end;
```

#### Demo

```unit Unit1;

{\$mode objfpc}{\$H+}
{\$modeswitch objectivec1}

interface

uses
Classes, Forms, Dialogs, StdCtrls,
CocoaAll, CocoaUtils, MacOSAll;

type

{ TForm1 }

TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private

public

end;

var
Form1: TForm1;

implementation

{\$R *.lfm}

{ TForm1 }

function IsMacDarkMode: Boolean;
var
sMode: string;
begin
sMode  := CFStringToStr( CFStringRef( NSApp.effectiveAppearance.name ));
Result := Pos('Dark', sMode) > 0;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
if(IsMacDarkMode) then
ShowMessage('Dark mode')
else
ShowMessage('Light mode');
end;

end.
```

### Opting out of dark mode

Mac systems automatically opt in any application linked against the macOS 10.14 or later SDK to both light and dark appearances. You can opt out of dark mode by including the NSRequiresAquaSystemAppearance key (with a value of YES) in your application’s Info.plist property list file. Setting this key to YES causes the system to ignore the user's preference and always apply a light appearance to your application.

### Opting in to dark mode

If you build your application against an earlier SDK but still want to support Dark Mode, include the NSRequiresAquaSystemAppearance key (with a value of NO) in your applications's Info.plist property list file. Do so only if your applications's appearance looks correct when running in macOS 10.14 and later with Dark Mode enabled.