Theming trong Flet

Học cách tùy chỉnh giao diện ứng dụng với theme và styling. ⏱️ 15 phút

🎯 Mục tiêu

Nắm vững:

Theme mode (Light/Dark)
Custom ColorScheme
Typography và Font
Control-level styling

🌗 Theme Mode với Declarative UI

Flet hỗ trợ 3 theme modes. Với Declarative UI, ta quản lý qua state:


import flet as ft
 
@ft.observable
class ThemeState:
    is_dark: bool = False
    
    def toggle(self):
        self.is_dark = not self.is_dark
 
state = ThemeState()
 
@ft.component
def ThemeToggle():
    return ft.Switch(
        label="Dark Mode",
        value=state.is_dark,
        on_change=lambda _: state.toggle(),
    )
 
@ft.component
def ThemeApp():
    return ft.Column([
        ThemeToggle(),
        ft.Text("Hello Flet!", size=24),
    ])
 
def main(page: ft.Page):
    # Thiết lập theme dựa trên state
    page.theme_mode = ft.ThemeMode.DARK if state.is_dark else ft.ThemeMode.LIGHT
    page.add(ThemeApp())
 
ft.run(main)

🎨 Custom Color Scheme


import flet as ft
 
# Định nghĩa themes
LIGHT_THEME = ft.Theme(
    color_scheme=ft.ColorScheme(
        primary=ft.Colors.PURPLE,
        secondary=ft.Colors.ORANGE,
        surface=ft.Colors.WHITE,
        background=ft.Colors.GREY_100,
        error=ft.Colors.RED,
    ),
)
 
DARK_THEME = ft.Theme(
    color_scheme=ft.ColorScheme(
        primary=ft.Colors.PURPLE_200,
        secondary=ft.Colors.ORANGE_200,
        surface=ft.Colors.GREY_900,
        background=ft.Colors.BLACK,
    ),
)
 
@ft.observable
class ThemeState:
    is_dark: bool = False
    
    def toggle(self):
        self.is_dark = not self.is_dark
 
state = ThemeState()
 
@ft.component
def ButtonsPreview():
    return ft.Row([
        ft.FilledButton("Filled"),
        ft.ElevatedButton("Elevated"),
        ft.OutlinedButton("Outlined"),
    ], wrap=True)
 
@ft.component
def ThemeDemo():
    return ft.Column([
        ft.Switch(
            label="Dark Mode",
            value=state.is_dark,
            on_change=lambda _: state.toggle(),
        ),
        ft.Divider(),
        ft.Text("Buttons Preview", weight=ft.FontWeight.BOLD),
        ButtonsPreview(),
    ], spacing=20)
 
def main(page: ft.Page):
    page.title = "Theme Demo"
    page.theme = LIGHT_THEME
    page.dark_theme = DARK_THEME
    page.theme_mode = ft.ThemeMode.DARK if state.is_dark else ft.ThemeMode.LIGHT
    page.padding = 30
    page.add(ThemeDemo())
 
ft.run(main)

🔤 Typography

Custom fonts và text styles:


import flet as ft
 
@ft.component
def TypographyDemo():
    return ft.Column([
        ft.Text("Default font", size=16),
        ft.Text("Bold Text", weight=ft.FontWeight.BOLD, size=20),
        ft.Text("Italic Text", italic=True, size=18),
        ft.Text("Colored Text", color=ft.Colors.BLUE, size=18),
    ], spacing=10)
 
def main(page: ft.Page):
    # Thêm custom font (đặt file .ttf trong thư mục assets)
    page.fonts = {
        "Roboto": "fonts/Roboto-Regular.ttf",
        "RobotoBold": "fonts/Roboto-Bold.ttf",
    }
    
    # Hoặc Google Fonts (tự động tải)
    page.fonts = {
        "Kanit": "Kanit",
        "Open Sans": "Open Sans",
    }
    
    page.theme = ft.Theme(font_family="Kanit")
    page.add(TypographyDemo())
 
ft.run(main)

🎛️ Control-level Styling

Styled Button Component


import flet as ft
 
@ft.component
def StyledButton(text: str, color=ft.Colors.GREEN):
    return ft.ElevatedButton(
        text,
        style=ft.ButtonStyle(
            color=ft.Colors.WHITE,
            bgcolor=color,
            padding=20,
            shape=ft.RoundedRectangleBorder(radius=10),
            elevation=5,
        ),
    )
 
@ft.component
def ButtonsRow():
    return ft.Row([
        StyledButton("Success", ft.Colors.GREEN),
        StyledButton("Warning", ft.Colors.ORANGE),
        StyledButton("Danger", ft.Colors.RED),
    ], spacing=10)
 
def main(page: ft.Page):
    page.add(ButtonsRow())
 
ft.run(main)

Styled Container Component


import flet as ft
 
@ft.component
def StyledCard(title: str, content: str):
    return ft.Container(
        content=ft.Column([
            ft.Text(title, weight=ft.FontWeight.BOLD, size=18),
            ft.Text(content, color=ft.Colors.GREY_600),
        ], spacing=5),
        width=250,
        padding=20,
        bgcolor=ft.Colors.BLUE_50,
        border=ft.border.all(2, ft.Colors.BLUE),
        border_radius=15,
        shadow=ft.BoxShadow(
            blur_radius=10,
            spread_radius=2,
            color=ft.Colors.BLACK26,
        ),
    )
 
@ft.component
def GradientCard(title: str):
    return ft.Container(
        content=ft.Text(title, color=ft.Colors.WHITE, size=20),
        width=200,
        height=100,
        alignment=ft.alignment.center,
        border_radius=15,
        gradient=ft.LinearGradient(
            begin=ft.alignment.top_left,
            end=ft.alignment.bottom_right,
            colors=[ft.Colors.BLUE_400, ft.Colors.PURPLE_400],
        ),
    )
 
@ft.component
def CardsDemo():
    return ft.Column([
        StyledCard("Card Title", "This is card content"),
        GradientCard("Gradient Card"),
    ], spacing=20)
 
def main(page: ft.Page):
    page.padding = 30
    page.add(CardsDemo())
 
ft.run(main)

🎯 Complete Theme Switcher


import flet as ft
 
@ft.observable
class ThemeState:
    is_dark: bool = False
    primary_color: str = "indigo"
    
    colors_map = {
        "indigo": (ft.Colors.INDIGO, ft.Colors.INDIGO_200),
        "green": (ft.Colors.GREEN, ft.Colors.GREEN_200),
        "purple": (ft.Colors.PURPLE, ft.Colors.PURPLE_200),
        "orange": (ft.Colors.ORANGE, ft.Colors.ORANGE_200),
    }
    
    def toggle_mode(self):
        self.is_dark = not self.is_dark
    
    def set_color(self, color: str):
        self.primary_color = color
    
    def get_primary(self):
        light, dark = self.colors_map.get(self.primary_color, (ft.Colors.INDIGO, ft.Colors.INDIGO_200))
        return dark if self.is_dark else light
 
state = ThemeState()
 
@ft.component
def ColorPicker():
    colors = ["indigo", "green", "purple", "orange"]
    
    return ft.Row([
        ft.Container(
            width=40,
            height=40,
            bgcolor=state.colors_map[c][0],
            border_radius=20,
            border=ft.border.all(3, ft.Colors.WHITE) if state.primary_color == c else None,
            on_click=lambda _, color=c: state.set_color(color),
        )
        for c in colors
    ], spacing=10)
 
@ft.component
def ComponentsPreview():
    return ft.Column([
        ft.Text("Preview", size=20, weight=ft.FontWeight.BOLD),
        ft.Divider(),
        ft.Row([
            ft.FilledButton("Filled"),
            ft.ElevatedButton("Elevated"),
            ft.OutlinedButton("Outlined"),
        ], wrap=True),
        ft.TextField(label="Sample Input"),
        ft.Slider(value=60),
        ft.ProgressBar(value=0.7),
        ft.Card(
            content=ft.Container(
                content=ft.ListTile(
                    leading=ft.Icon(ft.Icons.PERSON),
                    title=ft.Text("John Doe"),
                    subtitle=ft.Text("[email protected]"),
                ),
                padding=10,
            ),
        ),
    ], spacing=15)
 
@ft.component
def ThemeSettings():
    return ft.Card(
        content=ft.Container(
            content=ft.Column([
                ft.Text("Theme Settings", size=20, weight=ft.FontWeight.BOLD),
                ft.Divider(),
                ft.Row([
                    ft.Icon(ft.Icons.DARK_MODE if state.is_dark else ft.Icons.LIGHT_MODE),
                    ft.Text("Dark Mode"),
                    ft.Container(expand=True),
                    ft.Switch(
                        value=state.is_dark,
                        on_change=lambda _: state.toggle_mode(),
                    ),
                ]),
                ft.Text("Primary Color", weight=ft.FontWeight.W_500),
                ColorPicker(),
            ]),
            padding=20,
        ),
    )
 
@ft.component
def ThemeSwitcherApp():
    return ft.Row([
        ft.Container(content=ThemeSettings(), width=300),
        ft.VerticalDivider(),
        ft.Container(content=ComponentsPreview(), expand=True, padding=20),
    ], expand=True)
 
def main(page: ft.Page):
    page.title = "Theme Switcher"
    page.padding = 20
    
    # Dynamic theme based on state
    page.theme = ft.Theme(color_scheme=ft.ColorScheme(primary=state.get_primary()))
    page.dark_theme = ft.Theme(color_scheme=ft.ColorScheme(primary=state.get_primary()))
    page.theme_mode = ft.ThemeMode.DARK if state.is_dark else ft.ThemeMode.LIGHT
    
    page.add(ThemeSwitcherApp())
 
ft.run(main)

📋 ColorScheme Properties

Property	Description
`primary`	Màu chính (buttons, links)
`secondary`	Màu phụ
`surface`	Màu surfaces (cards)
`background`	Màu nền
`error`	Màu lỗi
`on_primary`	Text trên primary
`on_surface`	Text trên surface

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