coco
72 lines
1.9 KiB
Markdown
72 lines
1.9 KiB
Markdown
# PreviewParameter
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You can use **@PreviewParameter** to provide sample data for your Composables.
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Let's say you have the following Composable and you want to generate a preview.
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```kotlin
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data class User(val name :String,val age:Int)
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@Composable
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fun UserInfo(user:User) {
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Text(user.name+ " "+user.age)
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}
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```
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Because UserInfo needs a User you can't directly use @Preview.
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One way is to wrap your Composable in a Composable that provides a User
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```kotlin
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@Preview
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@Composable
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fun UserPreview() {
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UserInfo(user = User("Jens", 31))
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}
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```
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An other way is to use @PreviewParameter on the parameter. With PreviewParameter you can set a class
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which will provide values for the needed User
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```kotlin
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@Preview
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@Composable
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fun UserInfo(@PreviewParameter(SampleUserProvider::class) user:User) {
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Text(user.name+ " "+user.age)
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}
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```
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### Create PreviewParameterProvider
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**SampleUserProvider::class** will be the class which provides a User.
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To create a PreviewParameterProvider you need to implement the interface PreviewParameterProvider.
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The interface has two properties.
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**values** is a sequence of your sample data.
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```kotlin
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class SampleUserProvider: PreviewParameterProvider<User> {
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override val values = sequenceOf(User("Jens",31),User("Jim",44))
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}
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```
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### Use PreviewParameterProvider
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You can annotate your parameter with @PreviewParameter and the class which provides the sample data.
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```kotlin
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@Preview
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@Composable
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fun UserInfo(@PreviewParameter(SampleUserProvider::class) user:User) {
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Text(user.name+ " "+user.age)
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}
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```
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Now Android Studio will generate a preview of the Composable for every value that your provider provides.
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<p align="center">
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<img src ="../../../images/general/preview/previewParam1.png" height=100 width=300 />
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</p>
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You can limit the amount of previews by settings a limit to PreviewParameter.
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```kotlin
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@PreviewParameter(SampleUserProvider::class,1)
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```
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