Material Design系列第五篇——Working with Drawables

Working with Drawables

This lesson teaches you to

1. Tint Drawable Resources
2. Extract Prominent Colors from an Image
3. Create Vector Drawables

You should also read

• Material design specification
• Material design on Android

The following capabilities for drawables help you implement material design in your apps:

• Drawable tinting
• Prominent color extraction
• Vector drawables

This lesson shows you how to use these features in your app.

Tint Drawable Resources

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With Android 5.0 (API level 21) and above, you can tint bitmaps and nine-patches defined as alpha masks. You can tint them with color resources or theme attributes that resolve to color resources (for example, ?android:attr/colorPrimary). Usually, you create these assets only once and color them automatically to match your theme.

You can apply a tint to BitmapDrawable or NinePatchDrawable objects with the setTint() method. You can also set the tint color and mode in your layouts with the android:tint and android:tintMode attributes.

Extract Prominent Colors from an Image

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The Android Support Library r21 and above includes the Palette class, which lets you extract prominent colors from an image. This class extracts the following prominent colors:

• Vibrant
• Vibrant dark
• Vibrant light
• Muted
• Muted dark
• Muted light

To extract these colors, pass a Bitmap object to the Palette.generate() static method in the background thread where you load your images. If you can't use that thread, call the Palette.generateAsync() method and provide a listener instead.

You can retrieve the prominent colors from the image using the getter methods in the Palette class, such as Palette.getVibrantColor.

To use the Palette class in your project, add the following Gradle dependency to your app's module:

dependencies {
    ...
    compile 'com.android.support:palette-v7:21.0.+'
}

For more information, see the API reference for the Palette class.

Create Vector Drawables

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Video

Android Vector Graphics

In Android 5.0 (API Level 21) and above, you can define vector drawables, which scale without losing definition. You need only one asset file for a vector image, as opposed to an asset file for each screen density in the case of bitmap images. To create a vector image, you define the details of the shape inside a <vector> XML element.

The following example defines a vector image with the shape of a heart:

<!-- res/drawable/heart.xml -->
<vector xmlns:android="http://schemas.android.com/apk/res/android"
    <!-- intrinsic size of the drawable -->
    android:height="256dp"
    android:width="256dp"
    <!-- size of the virtual canvas -->
    android:viewportWidth="32"
    android:viewportHeight="32">
 
  <!-- draw a path -->
  <pathandroid:fillColor="#8fff"
      android:pathData="M20.5,9.5
                        c-1.955,0,-3.83,1.268,-4.5,3
                        c-0.67,-1.732,-2.547,-3,-4.5,-3
                        C8.957,9.5,7,11.432,7,14
                        c0,3.53,3.793,6.257,9,11.5
                        c5.207,-5.242,9,-7.97,9,-11.5
                        C25,11.432,23.043,9.5,20.5,9.5z"/>
</vector>

Vector images are represented in Android as VectorDrawable objects. For more information about the pathData syntax, see the SVG Path reference. For more information about animating the properties of vector drawables, see Animating Vector Drawables.