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OS windows management

What is covered

In this tutorial we will show you how to work with windows using Compose for Desktop.

Windows creation

The main class for creating windows is AppWindow. The easiest way to create and launch a new window is to use an instance of the AppWindow class and call its method show(). You can see an example below:

import androidx.compose.desktop.AppWindow

fun main() {
    AppWindow().show {
        // content
    }
}

There are two types of window – modal and regular. Below are the functions for creating each type of window:

Window – regular window type.
Dialog – modal window type. Such a window locks its parent window until the user completes working with it and closes the modal window.

You can see an example of both types of window below.

import androidx.compose.desktop.Window
import androidx.compose.foundation.Text
import androidx.compose.material.Button
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.window.Dialog

fun main() {
    Window {
        val dialogState = remember { mutableStateOf(false) }

        Button(onClick = { dialogState.value = true }) {
            Text(text = "Open dialog")
        }

        if (dialogState.value) {
            Dialog(
                onDismissEvent = { dialogState.value = false }
            ) {
                // dialog's content
            }
        }
    }
}

Window attributes

Each window has 9 parameters, all of them could be omitted and have default values:

title – window title
size – initial window size
location – initial window position
centered – set the window to the center of the display
icon – window icon
menuBar – window context menu
undecorated – disable native border and title bar of the window
events – window events
onDismissEvent – event when removing the window content from a composition

An example of using window parameters in the creation step:

import androidx.compose.desktop.AppManager
import androidx.compose.desktop.Window
import androidx.compose.desktop.WindowEvents
import androidx.compose.foundation.Text
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material.Button
import androidx.compose.runtime.mutableStateOf
import androidx.compose.ui.Alignment
import androidx.compose.ui.input.key.Key
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.IntOffset
import androidx.compose.ui.unit.IntSize
import androidx.compose.ui.window.MenuItem
import androidx.compose.ui.window.KeyStroke
import androidx.compose.ui.window.Menu
import androidx.compose.ui.window.MenuBar
import java.awt.Color
import java.awt.Graphics2D
import java.awt.image.BufferedImage

fun main() {
    val count = mutableStateOf(0)
    val windowPos = mutableStateOf(IntOffset.Zero)

    Window(
        title = "MyApp",
        size = IntSize(400, 250),
        location = IntOffset(100, 100),
        centered = false, // true - by default
        icon = getMyAppIcon(),
        menuBar = MenuBar(
            Menu(
                name = "Actions",
                MenuItem(
                    name = "Increment value",
                    onClick = {
                        count.value++
                    },
                    shortcut = KeyStroke(Key.I)
                ),
                MenuItem(
                    name = "Exit",
                    onClick = { AppManager.exit() },
                    shortcut = KeyStroke(Key.X)
                )
            )
        ),
        undecorated = true, // false - by default
        events = WindowEvents(
            onRelocate = { location ->
                windowPos.value = location
            }
        )
    ) {
        // content
        Box(
            modifier = Modifier.fillMaxSize(),
            alignment = Alignment.Center
        ) {
            Column {
                Text(text = "Location: ${windowPos.value} Value: ${count.value}")
                Button(
                    onClick = {
                        AppManager.exit()
                    }
                ) {
                    Text(text = "Close app")
                }
            }
        }
    }
}

fun getMyAppIcon() : BufferedImage {
    val size = 256
    val image = BufferedImage(size, size, BufferedImage.TYPE_INT_ARGB)
    val graphics = image.createGraphics()
    graphics.setColor(Color.orange)
    graphics.fillOval(0, 0, size, size)
    graphics.dispose()
    return image
}

Window properties

AppWindow parameters correspond to the following properties:

title – window title
width – window width
height – window height
x – position of the left top corner of the window along the X axis
y – position of the left top corner of the window along the Y axis
icon – window icon image
events – window events

To get the properties of a window, it is enough to have a link to the current or specific window. There are two ways to get the current focused window:

Using the global environment:

import androidx.compose.desktop.AppWindowAmbient
import androidx.compose.desktop.Window
import androidx.compose.foundation.Text
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material.Button
import androidx.compose.runtime.mutableStateOf
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.IntOffset

fun main() {
    val windowPos = mutableStateOf(IntOffset.Zero)
    
    Window {
        val current = AppWindowAmbient.current
        
        // content
        Box(
            modifier = Modifier.fillMaxSize(),
            alignment = Alignment.Center
        ) {
            Column {
                Text(text = "Location: ${windowPos.value}")
                Button(
                    onClick = {
                        if (current != null) {
                            windowPos.value = IntOffset(current.x, current.y)
                        }
                    }
                ) {
                    Text(text = "Print window location")
                }
            }
        }
    }
}

Using AppManager:

import androidx.compose.desktop.AppManager
import androidx.compose.desktop.Window
import androidx.compose.foundation.Text
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material.Button
import androidx.compose.runtime.mutableStateOf
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.IntOffset

fun main() {
    val windowPos = mutableStateOf(IntOffset.Zero)

    Window {
        // content
        Box(
            modifier = Modifier.fillMaxSize(),
            alignment = Alignment.Center
        ) {
            Column {
                Text(text = "Location: ${windowPos.value}")
                Button(
                    onClick = {
                        val current = AppManager.focusedWindow
                        if (current != null) {
                            windowPos.value = IntOffset(current.x, current.y)
                        }
                    }
                ) {
                    Text(text = "Print window location")
                }
            }
        }
    }
}

Using the following methods, you can change the properties of the AppWindow:

setTitle(title: String) – window title
setSize(width: Int, height: Int) – window size
setLocation(x: Int, y: Int) – window position
setWindowCentered() – set the window to the center of the display
setIcon(image: BufferedImage?) – window icon

import androidx.compose.desktop.AppWindowAmbient
import androidx.compose.desktop.Window
import androidx.compose.foundation.Text
import androidx.compose.material.Button

fun main() {
    Window {
        val current = AppWindowAmbient.current

        // content
        Button(
            onClick = {
                if (current != null) {
                    current.setWindowCentered()
                }
            }
        ) {
            Text(text = "Center the window")
        }
    }
}

Window events

Events can be defined using the events parameter in the window creation step or redefine using the events property at runtime. Actions can be assigned to the following window events:

onOpen – event during window opening
onClose – event during window closing
onMinimize – event during window minimizing
onMaximize – event during window maximizing
onRestore – event during restoring window size after window minimize/maximize
onFocusGet – event when window gets focus
onFocusLost – event when window loses focus
onResize – event on window resize (argument is window size as IntSize)
onRelocate – event of the window reposition on display (argument is window position as IntOffset)

import androidx.compose.desktop.Window
import androidx.compose.desktop.WindowEvents
import androidx.compose.foundation.Text
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material.Button
import androidx.compose.runtime.mutableStateOf
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.IntSize

fun main() {
    val windowSize = mutableStateOf(IntSize.Zero)
    val focused = mutableStateOf(false)
    
    Window(
        events = WindowEvents(
            onFocusGet = { focused.value = true },
            onFocusLost = { focused.value = false },
            onResize = { size ->
                windowSize.value = size
            }
        )
    ) {
        // content
        Box(
            modifier = Modifier.fillMaxSize(),
            alignment = Alignment.Center
        ) {
            Text(text = "Size: ${windowSize.value} Focused: ${focused.value}")
        }
    }
}

AppManager

The AppManager singleton is used to customize the behavior of the entire application. Its main features:

Description of common application events

AppManager.setEvents(
    onAppStart = { println("onAppStart") }, // invoked before the first window is created
    onAppExit = { println("onAppExit") } // invoked after all windows are closed
)

Customization of common application context menu

AppManager.setMenu(
    getCommonAppMenuBar() // custom function that returns MenuBar
)

Access to the application windows list

val windows = AppManager.windows

Getting the current focused window

val current = AppManager.focusedWindow

Application exit

AppManager.exit() // closes all windows

Access to Swing components

Compose for Desktop is tightly integrated with Swing at the top-level windows layer. For more detailed customization, you can access the JFrame class:

import androidx.compose.desktop.AppManager
import androidx.compose.desktop.Window
import androidx.compose.foundation.Text
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material.Button
import androidx.compose.runtime.mutableStateOf
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier

fun main() {
    val scaleFactor = mutableStateOf(0.0)
    Window {
        // content
        Box(
            modifier = Modifier.fillMaxSize(),
            alignment = Alignment.Center
        ) {
            Column {
                Button(
                    onClick = {
                        val current = AppManager.focusedWindow
                        if (current != null) {
                            val jFrame = current.window
                            // do whatever you want with it
                            scaleFactor.value = jFrame.graphicsConfiguration.defaultTransform.scaleX
                        }
                    }
                ) {
                    Text(text = "Check display scaling factor")
                }
                Text(text = "Scaling factor: ${scaleFactor.value}}")
            }
        }
    }
}

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