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paris

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Define and apply styles to Android views programmatically

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# Paris
Paris lets you define and apply styles programmatically to Android views, including custom attributes.

* Apply styles programmatically at any time.
* Combine multiple styles together.
* Create styles programmatically (as opposed to using XML).
* Use annotations to easily support custom attributes (inspired by [Barber](https://github.com/hzsweers/barber)).
* Declare explicitly supported styles for your custom views.
* And much more...

## Installation

In your project's `build.gradle`:
```gradle
dependencies {
    implementation 'com.airbnb.android:paris:2.2.1'
    // Apply the Paris processor if you're using Paris annotations for code gen.
    kapt 'com.airbnb.android:paris-processor:2.2.1'
    // or if you are using Kotlin Symbol Processing
    ksp 'com.airbnb.android:paris-processor:2.2.1'
}
```

To use Paris in a library module see [Library Modules](../../wiki/Library-Modules).

## Quick Start

### Applying an XML-Defined Style

```kotlin
myView.style(R.style.MyStyle)
```
<details><summary>Click to see the example in Java.</summary>

```java
Paris.style(myView).apply(R.style.MyStyle);
```
</details>

Where `myView` is an arbitrary view instance, `MyStyle` an XML-defined style, and `style` an extension function provided by Paris. Many but not all attributes are supported, for more see [Supported View Types and Attributes](../../wiki/Supported-View-Types-and-Attributes).

### Combining 2 or More Styles

```kotlin
myView.style {
 add(R.style.StyleA)
 add(R.style.StyleB)
 …
}
```
<details><summary>Click to see the example in Java.</summary>

```java
Paris.styleBuilder(myView)
 .add(R.style.StyleA)
 .add(R.style.StyleB)
 …
 .apply();
```
</details>

In cases where there's some overlap the attribute value from the last style added prevails. For more see [Combining Styles](../../wiki/Building-and-Applying-Styles#combining-styles).

### Defining Styles Programmatically

```kotlin
textView.style {
 // Using an actual value.
 textColor(Color.GREEN)
 // Or a resource.
 textSizeRes(R.dimen.my_text_size_small)
}
```
<details><summary>Click to see the example in Java.</summary>

```java
Paris.styleBuilder(textView)
 // Using an actual value.
 .textColor(Color.GREEN)
 // Or a resource.
 .textSizeRes(R.dimen.my_text_size_small)
 .apply();
```
</details>

Can be combined with style resources as well:
```kotlin
textView.style {
 // Adds all the attributes defined in the MyGreenTextView style.
 add(R.style.MyGreenTextView)
 textSizeRes(R.dimen.my_text_size_small)
}
```
<details><summary>Click to see the example in Java.</summary>

```java
Paris.styleBuilder(textView)
 // Adds all the attributes defined in the MyGreenTextView style.
 .add(R.style.MyGreenTextView)
 .textSizeRes(R.dimen.my_text_size_small)
 .apply();
```
</details>

For more see [Defining Styles Programmatically](../../wiki/Building-and-Applying-Styles#defining-styles-programmatically).

### Custom View Attributes

Attributes are declared as followed:
```xml
<declare-styleable name="MyView">
 <attr name="title" format="string" />
 <attr name="image" format="reference" />
 <attr name="imageSize" format="dimension" />
</declare-styleable>
```

The custom view is annotated with `@Styleable` and `@Attr`:
```kotlin
// The value here corresponds to the name chosen in declare-styleable.
@Styleable("MyView")
class MyView(…) : ViewGroup(…) {

init {
        // This call enables the custom attributes when used in XML layouts. It
        // extracts styling information from AttributeSet like it would a StyleRes.
        style(attrs)
    }

@Attr(R.styleable.MyView_title)
    fun setTitle(title: String) {
        // Automatically called with the title value (if any) when an AttributeSet
        // or StyleRes is applied to the MyView instance.
    }

@Attr(R.styleable.MyView_image)
    fun setImage(image: Drawable?) {
        // Automatically called with the image value (if any) when an AttributeSet
        // or StyleRes is applied to the MyView instance.
    }

@Attr(R.styleable.MyView_imageSize)
 fun setImageSize(@Px imageSize: Int) {
 // Automatically called with the imageSize value (if any) when an
 // AttributeSet or StyleRes is applied to the MyView instance.
 }
}
```
<details><summary>Click to see the example in Java.</summary>

```java
// The value here corresponds to the name chosen in declare-styleable.
@Styleable("MyView")
public class MyView extends ViewGroup {

public MyView(Context context) {
        super(context);
    }

public MyView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

public MyView(Context context, AttributeSet attrs, int defStyle) {
        this(context, attrs, defStyle);
        // This call enables the custom attributes when used in XML layouts. It
        // extracts styling information from AttributeSet like it would a StyleRes.
        Paris.style(this).apply(attrs);
    }

@Attr(R.styleable.MyView_title)
    public void setTitle(String title) {
        // Automatically called with the title value (if any) when an AttributeSet
        // or StyleRes is applied to the MyView instance.
    }

@Attr(R.styleable.MyView_image)
    public void setImage(Drawable image) {
        // Automatically called with the image value (if any) when an AttributeSet
        // or StyleRes is applied to the MyView instance.
    }

@Attr(R.styleable.MyView_imageSize)
 public void setImageSize(@Px int imageSize) {
 // Automatically called with the imageSize value (if any) when an
 // AttributeSet or StyleRes is applied to the MyView instance.
 }
}
```
</details>

The `@Attr`-annotated methods will be called by Paris when the view is inflated with an `AttributeSet` or when a style is applied.

For more see [Custom View Attributes](../../wiki/Custom-View-Attributes).

### Styling Subviews

Attributes are declared as followed for the 2 subviews we'd like to be able to style:
```xml
<declare-styleable name="MyHeader">
 <attr name="titleStyle" format="reference" />
 <attr name="subtitleStyle" format="reference" />
 ...
</declare-styleable>
```

The subview fields are annotated with `@StyleableChild`:
```kotlin
@Styleable("MyHeader")
class MyHeader(…) : ViewGroup(…) {

@StyleableChild(R.styleable.MyHeader_titleStyle)
 internal val title: TextView …
 
 @StyleableChild(R.styleable.MyHeader_subtitleStyle)
 internal val subtitle: TextView …
 
 init {
 style(attrs)
 }
}
```
<details><summary>Click to see the example in Java.</summary>

```java
@Styleable("MyHeader")
public class MyHeader extends ViewGroup {

@StyleableChild(R.styleable.MyHeader_titleStyle)
 TextView title;
 
 @StyleableChild(R.styleable.MyHeader_subtitleStyle)
 TextView subtitle;
 
 …
 // Make sure to call Paris.style(this).apply(attrs) during initialization.
}
```
</details>

The title and subtitle styles can now be part of `MyHeader` styles:
```xml
<MyHeader
 ...
 app:titleStyle="@style/Title2"
 app:subtitleStyle="@style/Regular" />
```

```kotlin
myHeader.style {
 // Defined in XML.
 titleStyle(R.style.Title2)
 // Defined programmatically.
 subtitleStyle {
 textColorRes(R.color.text_color_regular)
 textSizeRes(R.dimen.text_size_regular)
 }
}
```
<details><summary>Click to see the example in Java.</summary>

```java
Paris.styleBuilder(myHeader)
 // Defined in XML.
 .titleStyle(R.style.Title2)
 // Defined programmatically.
 .subtitleStyle((builder) -> builder
 .textColorRes(R.color.text_color_regular)
 .textSizeRes(R.dimen.text_size_regular))
 .apply();
```
</details>

**Attention:** Extension functions like `titleStyle` and `subtitleStyle` are generated during compilation by the Paris annotation processor. When new `@StyleableChild` annotations are added, the project must be (re)compiled once for the related functions to become available.

For more see [Styling Subviews](../../wiki/Custom-Views#styling-subviews).

### Linking Styles to Views

```kotlin
@Styleable
class MyView(…) : View(…) {

companion object {
        // For styles defined in XML.
        @Style
        val RED_STYLE = R.style.MyView_Red

// For styles defined programmatically.
 @Style
 val GREEN_STYLE = myViewStyle {
 background(R.color.green)
 }
 }
}
```
<details><summary>Click to see the example in Java.</summary>

```java
@Styleable
public class MyView extends View {

// For styles defined in XML.
    @Style
    static final int RED_STYLE = R.style.MyView_Red;

// For styles defined programmatically.
 @Style
 static void greenStyle(MyViewStyleApplier.StyleBuilder builder) {
 builder.background(R.color.green);
 }
}
```
</details>

Helper methods are generated for each linked style:
```kotlin
myView.style { addRed() } // Equivalent to style(R.style.MyView_Red)
myView.style { addGreen() } // Equivalent to add(MyView.GREEN_STYLE)

myView.style {
 addRed() // Equivalent to add(R.style.MyView_Red)
 addGreen() // Equivalent to add(MyView.GREEN_STYLE)
 …
}
```
<details><summary>Click to see the example in Java.</summary>

```java
Paris.style(myView).applyRed(); // Equivalent to apply(R.style.MyView_Red)
Paris.style(myView).applyGreen(); // No equivalent.

Paris.styleBuilder(myView)
 .addRed() // Equivalent to add(R.style.MyView_Red)
 .addGreen() // No equivalent.
 …
 .apply();
```
</details>

**Attention:** Extension functions like `addRed` and `addGreen` are generated during compilation by the Paris annotation processor. When new `@Style` annotations are added, the project must be (re)compiled once for the related functions to become available.

For more see [Linking Styles to Custom Views](../../wiki/Custom-Views#linking-styles-to-custom-views).

## Documentation

See examples and browse complete documentation at the [Paris Wiki](../../wiki).

If you still have questions, feel free to create a new issue.

## Contributing

We love contributions! Check out our [contributing guidelines](CONTRIBUTING.md) and be sure to follow our [code of conduct](CODE_OF_CONDUCT.md).

## License

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
```

paris

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