读书笔记:Android的Drawable

Android开发艺术探索:Android的Drawable

自定Drawable比自定义View的成本要低，使用非图片类型的Drawable有利于减少apk的体积。
可以通过 getIntrinsicWidth 和 getIntrinsicHeight 可已获取Drawable的内部宽高，并不是所有的Drawable都有内部宽高，例如ColorDrawable。

Drawable的分类

1.BitmapDrawable

<?xml version="1.0" encoding="utf-8"?>
<bitmap
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@[package:]drawable/drawable_resource"
    android:antialias=["true" | "false"]
    android:dither=["true" | "false"]
    android:filter=["true" | "false"]
    android:gravity=["top" | "bottom" | "left" | "right" | "center_vertical" |
                      "fill_vertical" | "center_horizontal" | "fill_horizontal" |
                      "center" | "fill" | "clip_vertical" | "clip_horizontal"]
    android:mipMap=["true" | "false"]
    android:tileMode=["disabled" | "clamp" | "repeat" | "mirror"] />

android:antialias 抗锯齿，开启之后会让图片变得平滑，虽然会降低一定的清晰度，应该开启。
android:dither 抖动效果，让高质量的图片在低质量的屏幕上保持较好的显示效果，防止过于失真，应该开启。
android:filter 过滤效果，当图片尺寸被拉伸或者压缩的时候，开启可以保持较好的显示效果，应该开启。
android:tileMode 平铺模式。

2.NinePatchDrawable

<nine-patch
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@[package:]drawable/drawable_resource"
    android:dither=["true" | "false"] />

.9格式的图片

3.ShapeDrawable

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape=["rectangle" | "oval" | "line" | "ring"] >
    <corners
        android:radius="integer"
        android:topLeftRadius="integer"
        android:topRightRadius="integer"
        android:bottomLeftRadius="integer"
        android:bottomRightRadius="integer" />
    <gradient
        android:angle="integer"
        android:centerX="integer"
        android:centerY="integer"
        android:centerColor="integer"
        android:endColor="color"
        android:gradientRadius="integer"
        android:startColor="color"
        android:type=["linear" | "radial" | "sweep"]
        android:useLevel=["true" | "false"] />
    <padding
        android:left="integer"
        android:top="integer"
        android:right="integer"
        android:bottom="integer" />
    <size
        android:width="integer"
        android:height="integer" />
    <solid
        android:color="color" />
    <stroke
        android:width="integer"
        android:color="color"
        android:dashWidth="integer"
        android:dashGap="integer" />
</shape>

solide 纯色填充
gradient 渐变填充
stroke 描边
size 设置的就是Drawable的固定宽高，getIntrinsicWidth 和 getIntrinsicHeight 方式获取的，但当View做为背景Drawable还是会拉伸或者缩小为View的大小。(固定宽高还是不变)

4.LayerDrawable

<?xml version="1.0" encoding="utf-8"?>
<layer-list
    xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:drawable="@[package:]drawable/drawable_resource"
        android:id="@[+][package:]id/resource_name"
        android:top="dimension"
        android:right="dimension"
        android:bottom="dimension"
        android:left="dimension" />
</layer-list>

多个Drawable叠加效果

5.StateListDrawable

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android"
    android:constantSize=["true" | "false"]
    android:dither=["true" | "false"]
    android:variablePadding=["true" | "false"] >
    <item
        android:drawable="@[package:]drawable/drawable_resource"
        android:state_pressed=["true" | "false"]
        android:state_focused=["true" | "false"]
        android:state_hovered=["true" | "false"]
        android:state_selected=["true" | "false"]
        android:state_checkable=["true" | "false"]
        android:state_checked=["true" | "false"]
        android:state_enabled=["true" | "false"]
        android:state_activated=["true" | "false"]
        android:state_window_focused=["true" | "false"] />
</selector>

Drawable集合，不同的状态显示不同的View

6.LevelListDrawable

<?xml version="1.0" encoding="utf-8"?>
<level-list
    xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:drawable="@drawable/drawable_resource"
        android:maxLevel="integer"
        android:minLevel="integer" />
</level-list>

Drawable集合，每个Drawable都有一个Level，根据不同的等级，LevelListDrawable会切换显示对应的Drawable。

7.TransitionDrawable

<?xml version="1.0" encoding="utf-8"?>
<transition
xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:drawable="@[package:]drawable/drawable_resource"
        android:id="@[+][package:]id/resource_name"
        android:top="dimension"
        android:right="dimension"
        android:bottom="dimension"
        android:left="dimension" />
</transition>

用于两个Drawable之间淡入淡出的效果，需要调用 startTransition reverseTransition:

ImageButton button = (ImageButton) findViewById(R.id.button);
TransitionDrawable drawable = (TransitionDrawable) button.getDrawable();
drawable.startTransition(500);

8.InsetDrawable

<?xml version="1.0" encoding="utf-8"?>
<inset
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:drawable="@drawable/drawable_resource"
    android:insetTop="dimension"
    android:insetRight="dimension"
    android:insetBottom="dimension"
    android:insetLeft="dimension" />

A drawable defined in XML that insets another drawable by a specified distance. This is useful when a View needs a background that is smaller than the View’s actual bounds.

9.ScaleDrawble

<?xml version="1.0" encoding="utf-8"?>
<scale
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:drawable="@drawable/drawable_resource"
    android:scaleGravity=["top" | "bottom" | "left" | "right" | "center_vertical" |
                          "fill_vertical" | "center_horizontal" | "fill_horizontal" |
                          "center" | "fill" | "clip_vertical" | "clip_horizontal"]
    android:scaleHeight="percentage"
    android:scaleWidth="percentage" />

根据自己的level(默认是0)将指定的Drawable缩放到一定比例。

View scaleView = findViewById(R.id.scale);
ScaleDrawable scaleDrawable = scaleView.getBackground();
scaleDrawable.setLevel(1);

10.ClipDrawable

<?xml version="1.0" encoding="utf-8"?>
<clip
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:drawable="@drawable/drawable_resource"
    android:clipOrientation=["horizontal" | "vertical"]
    android:gravity=["top" | "bottom" | "left" | "right" | "center_vertical" |
                     "fill_vertical" | "center_horizontal" | "fill_horizontal" |
                     "center" | "fill" | "clip_vertical" | "clip_horizontal"] />

根据当前的level剪裁另一个Drawable

ImageView imageview = (ImageView) findViewById(R.id.image);
ClipDrawable drawable = (ClipDrawable) imageview.getDrawable();
drawable.setLevel(drawable.getLevel() + 1000);

自定义Drawable

主要有两个用途:ImageView的图像显示和View的背景。

Drawable书中的示例代码:

public class CustomDrawable extends Drawable {
    private Paint mPaint;

    public CustomDrawable(int color) {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setColor(color);
    }

    @Override
    public void draw(Canvas canvas) {
        final Rect r = getBounds();//获取实际区域大小，一般和View的尺寸相同
        float cx = r.exactCenterX();
        float cy = r.exactCenterY();
        canvas.drawCircle(cx, cy, Math.min(cx, cy), mPaint);
    }

    @Override
    public void setAlpha(int alpha) {
        mPaint.setAlpha(alpha);
        invalidateSelf();

    }

    @Override
    public void setColorFilter(ColorFilter cf) {
        mPaint.setColorFilter(cf);
        invalidateSelf();
    }

    @Override
    public int getOpacity() {
        // not sure, so be safe
        return PixelFormat.TRANSLUCENT;
    }

        //用与给View使用wrap_content的时候提供下尺寸
    @Override
    public int getIntrinsicHeight() {
        return super.getIntrinsicHeight();
    }

    @Override
    public int getIntrinsicWidth() {
        return super.getIntrinsicWidth();
    }

}