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# Compose Multiplatform mobile application

> Compose Multiplatform is in Alpha. It may change incompatibly and require manual migration in the future.

You can use this template to start developing your own [Compose Multiplatform](https://github.com/JetBrains/compose-multiplatform) application.
The result will be  a Kotlin Multiplatform project targeting Android and iOS.

![](readme_images/banner.png)

## Set up an environment

> **Important**. You will need a Mac with macOS to write and run iOS-specific code on simulated or real devices.
> This is an Apple requirement.

To work with this template, you need the following:

* A machine running a recent version of macOS
* [Xcode](https://apps.apple.com/us/app/xcode/id497799835)
* [Android Studio](https://developer.android.com/studio)
* [Kotlin Multiplatform Mobile plugin](https://plugins.jetbrains.com/plugin/14936-kotlin-multiplatform-mobile)
* [CocoaPods dependency manager](https://kotlinlang.org/docs/native-cocoapods.html)

### Check your environment

Before you start, use the [KDoctor](https://github.com/Kotlin/kdoctor) tool to ensure you have all the tools and that your development environment is configured correctly.

1. Install KDoctor with [Homebrew](https://brew.sh/):

    ```text
    brew install kdoctor
    ```

2. Run KDoctor in your terminal:

    ```text
    kdoctor
    ```

If everything is set up correctly, you'll see a valid output:

```text
Environment diagnose (to see all details, use -v option):
[✓] Operation System
[✓] Java
[✓] Android Studio
[✓] Xcode
[✓] Cocoapods

Conclusion:
  ✓ Your system is ready for Kotlin Multiplatform Mobile Development!
```

Otherwise, KDoctor will highlight which parts of your setup still need configuration and suggest how to fix them.

## Examine the project structure

1. Open the project in Android Studio.
2. Switch the project view from **Android** to **Project** to see all the files and targets belonging to the project.

<img src="readme_images/open_project_view.png" height="300px">

Your Compose Multiplatform project includes three modules:

### shared

This is a Kotlin module that contains the logic common for both Android and iOS applications, the code you share between platforms.

This `shared` module is also where you write your Compose Multiplatform code.
You can find the shared root `@Composable` function for your app in `shared/src/commonMain/kotlin/App.kt`.

It uses Gradle as the build system. You can add dependencies and change settings in `shared/build.gradle.kts`.
The shared module builds into an Android library and an iOS framework.

### androidApp

This is a Kotlin module that builds into an Android application. It uses Gradle as the build system.
The `androidApp` module depends on and uses the shared module as a regular Android library.

### iosApp

This is an Xcode project that builds into an iOS application.
It depends on and uses the shared module as a CocoaPods dependency.

## Run your application

### On Android

To run your application on an Android emulator:

1. Create an [Android virtual device](https://developer.android.com/studio/run/managing-avds#createavd).
2. In the list of run configurations, select `androidApp`.
3. Choose your virtual device and click **Run**.

<img src="readme_images/run_on_android.png" height="60px">
<img src="readme_images/android_app_running.png" height="200px">

<details>
  <summary>Alternatively, use Gradle</summary>

To install an Android application on a real device Android device or an emulator, run `./gradlew installDebug` in the terminal.

</details>

### On iOS

#### Running on an iOS simulator

Once you have configured your environment correctly,
you can select which iOS simulator to run your application in Android Studio by modifying the `iosApp` run configuration.

In the list of run configurations, select **Edit Configurations** and navigate to **iOS Application** | **iosApp**.
In the **Execution target** list, select your target device.

<img src="readme_images/edit_run_config.png" height="200px">
<img src="readme_images/target_device.png">

Press the **Run** button to run your Compose Multiplatform app on the iOS simulator.

<img src="readme_images/hello_world_ios.png" height="200px">

#### Running on a real iOS device

You can run your Compose Multiplatform application on a real device. To do that, you'll need the following:

* `TEAM_ID` associated with your [Apple ID](https://support.apple.com/en-us/HT204316)
* The iOS device registered in Xcode

Before you continue, we suggest creating a simple "Hello, world!" project in Xcode to ensure you can successfully run apps on your device.
You can follow the instructions below or watch this [this Standford CS193P lecture recording](https://youtu.be/bqu6BquVi2M?start=716&end=1399).

<details>

<summary>How to create and run a simple project in Xcode</summary>

1. On the Xcode welcome screen, select **Create a new project in Xcode**.
2. On the **iOS** tab, choose the **App** template. Click **Next**.
3. Specify the product name and keep other settings default. Click **Next**.
4. Select where to store the project on your computer and click **Create**. You'll see an app that displays "Hello, world!" on the device screen.
5. At the top of your Xcode screen, click on a device name near the **Run** button.
6. Plug in your device to the computer. You'll see this device in the list of run options.
7. Choose your device and click **Run**.

</details>

##### Finding your Team ID

In the terminal, run `kdoctor --team-ids` to find your Team ID.
KDoctor will list all Team IDs currently configured on your system, for example:

```text
3ABC246XYZ (Max Sample)
ZABCW6SXYZ (SampleTech Inc.)
```

<details>
<summary>Alternative way of finding your Team ID</summary>

If KDoctor doesn't work for you, try this alternative method:

1. In Android Studio, run the `iosApp` configuration with the selected real device. The build should fail.
2. Go to Xcode and select **Open a project or file**.
3. Navigate to the `iosApp/iosApp.xcworkspace` file of your project.
4. In the left menu, select `iosApp`.
5. Navigate to **Signing & Capabilities**.
6. In the **Team** list, select your personal team.

   If you haven't set up your team yet, use the **Add account** option and follow the steps.

</details>

To run the application, set the `TEAM_ID` associated with your Apple ID:

1. In the template, navigate to the `iosApp/Configuration/Config.xcconfig` file.
2. Set your `TEAM_ID`.
3. Re-open the project in Android Studio. It should show the registered iOS device in the `iosApp` run configuration.

## Make your first changes

In Android Studio, navigate to the `shared/src/commonMain/kotlin/App.kt` file.
It's the common entry point for your Compose Multiplatform app. 
Here, you see the code responsible for rendering the "Hello, World!" button and the animated Compose Multiplatform logo:

```kotlin
@OptIn(ExperimentalResourceApi::class)
@Composable
internal fun App() {
    MaterialTheme {
        var greetingText by remember { mutableStateOf("Hello, World!") }
        var showImage by remember { mutableStateOf(false) }
        Column(Modifier.fillMaxWidth(), horizontalAlignment = Alignment.CenterHorizontally) {
            Button(onClick = {
                greetingText = "Hello, ${getPlatformName()}"
                showImage = !showImage
            }) {
                Text(greetingText)
            }
            AnimatedVisibility(showImage) {
                Image(
                    painterResource("compose-multiplatform.xml"),
                    null
                )
            }
        }
    }
}
```

Update the shared code by adding a text field that will update the name displayed on the button:

```diff
@OptIn(ExperimentalResourceApi::class)
@Composable
internal fun App() {
    MaterialTheme {
        var greetingText by remember { mutableStateOf("Hello, World!") }
        var showImage by remember { mutableStateOf(false) }
        Column(Modifier.fillMaxWidth(), horizontalAlignment = Alignment.CenterHorizontally) {
            Button(onClick = {
                greetingText = "Hello, ${getPlatformName()}"
                showImage = !showImage
            }) {
                Text(greetingText)
            }
+           TextField(greetingText, onValueChange = { greetingText = it })
            AnimatedVisibility(showImage) {
                Image(
                    painterResource("compose-multiplatform.xml"),
                    null
                )
            }
        }
    }
}
```

You'll see this change reflected on both the Android and iOS apps:

<img src="readme_images/text_field_added.png" height="200px">

## How to configure the iOS application

You can further configure the basic properties of your iOS app using this template without opening Xcode.
In Android Studio, navigate to the `iosApp/Configuration/Config.xcconfig` configuration file. It contains:

* `APP_NAME`, a target executable and an application bundle name
* `BUNDLE_ID`  that [uniquely identifies the app throughout the system](https://developer.apple.com/documentation/bundleresources/information_property_list/cfbundleidentifier#discussion)
* `TEAM_ID`, [a unique identifier generated by Apple that's assigned to your team](https://developer.apple.com/help/account/manage-your-team/locate-your-team-id/#:~:text=A%20Team%20ID%20is%20a,developer%20in%20App%20Store%20Connect)

To configure the `APP_NAME` option, open `Config.xcconfig` in any text editor *before opening* the project in Android Studio, and set the desired name.

If you need to change this option after you open the project in Android Studio, do the following:

1. Close the project in Android Studio.
2. Run `./cleanup.sh` in your terminal.
3. Change the setting.
4. Open the project in Android Studio again.

To configure advanced settings, use Xcode. After opening the project in Android Studio,
go to Xcode and open the `iosApp/iosApp.xcworkspace` file, and make changes.