ShapeDrawable和GradientDrawable
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# 0x00 前言
之前在项目中封装了一个ShapeDrawable，其中可以设置fill 或 stroke，
通过RoundRectShape，
```
RoundRectShape(float[] outerRadii, RectF inset,float[] innerRadii)
```
通过 outerRadii 设置圆角，inset 传宽度完成 stroke，传 null 实现 fill 。
有一天同事发现无法既设置描边的颜色，又设置填充的颜色。
查了一下发现(http://blog.csdn.net/lonelyroamer/article/details/8254592)
本文想了解，
* 它们有什么不同
* drawable 文件是如何加载的
* ShapeDrawable 的目的是什么
# 0x01 ShapeDrawable 和 GradientDrawable的异同
## 1.1 ShapeDrawable
(https://developer.android.google.cn/reference/android/graphics/drawable/ShapeDrawable.html)
(https://developer.android.google.cn/guide/topics/graphics/2d-graphics.html#shape-drawable)
(https://developer.android.google.cn/guide/topics/resources/drawable-resource.html#Shape)
我们可以简单了解到，ShapeDrawable可用于画平面图形，它持有一个 (https://developer.android.google.cn/reference/android/graphics/drawable/shapes/Shape.html) 对象。
它的android.graphics.drawable.ShapeDrawable#draw方法是调用的
android.graphics.drawable.shapes.Shape#draw
我们通过给其设置不同的Shape可以绘制不同的形状，而通过设置Paint可以控制颜色等。
```
if (state.mShape != null) {
// need the save both for the translate, and for the (unknown)
// Shape
final int count = canvas.save();
canvas.translate(r.left, r.top);
onDraw(state.mShape, canvas, paint);
canvas.restoreToCount(count);
} else {
//这里可以解释不指定Shape时默认是矩形
canvas.drawRect(r, paint);
}
```
## 1.2 GradientDrawable
(https://developer.android.google.cn/reference/android/graphics/drawable/GradientDrawable.html)
可以用于颜色渐变，各种形状等。
Gradient有一Shape，但是它的Shape是以下之一。
`RECTANGLE, OVAL, LINE, RING`
它虽然也可以不同的形状，但和ShapeDrawable不同，它是使用cavas的不同的方法绘制
```
android.graphics.Canvas#drawRoundRect(android.graphics.RectF, float, float, android.graphics.Paint)
android.graphics.Canvas#drawOval(android.graphics.RectF, android.graphics.Paint)
android.graphics.Canvas#drawLine
android.graphics.Canvas#drawPath
```
### 1.2.1 虚线是怎么实现的
```
android.graphics.drawable.GradientDrawable#inflate
android.graphics.drawable.GradientDrawable#inflateChildElements
android.graphics.drawable.GradientDrawable#updateGradientDrawableStroke
android.graphics.drawable.GradientDrawable#setStroke(int, android.content.res.ColorStateList, float, float)
android.graphics.drawable.GradientDrawable#setStrokeInternal
DashPathEffect e = null;
if (dashWidth > 0) {
e = new DashPathEffect(new float[] { dashWidth, dashGap }, 0);
}
mStrokePaint.setPathEffect(e);
/**
* PathEffect is the base class for objects in the Paint that affect
* the geometry of a drawing primitive before it is transformed by the
* canvas' matrix and drawn.
*/
public class PathEffect {
protected void finalize() throws Throwable {
nativeDestructor(native_instance);
native_instance = 0;// Other finalizers can still call us.
}
private static native void nativeDestructor(long native_patheffect);
long native_instance;
}
```
# 0x02 drawable文件是如何加载的
```
android.view.LayoutInflater#inflate(int, android.view.ViewGroup)
android.view.LayoutInflater#inflate(int, android.view.ViewGroup, boolean)
android.view.LayoutInflater#inflate(org.xmlpull.v1.XmlPullParser, android.view.ViewGroup, boolean)
android.view.LayoutInflater#createViewFromTag(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet)
android.view.LayoutInflater#createViewFromTag(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet, boolean)
mFactory2.onCreateView
android.support.v7.app.AppCompatDelegateImplV9#onCreateView(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet)
android.support.v7.app.AppCompatDelegateImplV9#createView
android.support.v7.app.AppCompatViewInflater#createView(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet, boolean, boolean, boolean, boolean)
这里可以解释为什么TextView会被加载为AppCompatTextView
...
switch (name) {
case "TextView":
view = new AppCompatTextView(context, attrs);
...
android.support.v7.widget.AppCompatTextView#AppCompatTextView(android.content.Context, android.util.AttributeSet)
android.widget.TextView#TextView(android.content.Context, android.util.AttributeSet, int, int)
android.view.View#View(android.content.Context, android.util.AttributeSet, int, int)
在加载view的时候获取drawable
...
final int N = a.getIndexCount();
for (int i = 0; i < N; i++) {
int attr = a.getIndex(i);
switch (attr) {
case com.android.internal.R.styleable.View_background:
background = a.getDrawable(attr);
...
android.content.res.TypedArray#getDrawable
android.content.res.Resources#loadDrawable
android.content.res.ResourcesImpl#loadDrawable
会加载一些缓存，没有的时候才执行加载
android.content.res.ResourcesImpl#loadDrawableForCookie
...
if (file.endsWith(".xml")) {
final XmlResourceParser rp = loadXmlResourceParser(
file, id, value.assetCookie, "drawable");
dr = Drawable.createFromXml(wrapper, rp, theme);
rp.close();
} else {
final InputStream is = mAssets.openNonAsset(
value.assetCookie, file, AssetManager.ACCESS_STREAMING);
dr = Drawable.createFromResourceStream(wrapper, value, is, file, null);
is.close();
}
...
android.graphics.drawable.Drawable#createFromXml(android.content.res.Resources, org.xmlpull.v1.XmlPullParser, android.content.res.Resources.Theme)
android.graphics.drawable.Drawable#createFromXmlInner(android.content.res.Resources, org.xmlpull.v1.XmlPullParser, android.util.AttributeSet, android.content.res.Resources.Theme)
android.graphics.drawable.DrawableInflater#inflateFromXml
最终到了加载的地方
...
Drawable drawable = inflateFromTag(name);
if (drawable == null) {
drawable = inflateFromClass(name);
}
drawable.inflate(mRes, parser, attrs, theme);
return drawable;
android.graphics.drawable.DrawableInflater#inflateFromTag
可以看到 shape标签被加载为了GradientDrawable，而并不是ShapeDrawable，并且没有任何一个可以加载为ShapeDrawable。
switch (name) {
case "selector":
return new StateListDrawable();
case "animated-selector":
return new AnimatedStateListDrawable();
case "level-list":
return new LevelListDrawable();
case "layer-list":
return new LayerDrawable();
case "transition":
return new TransitionDrawable();
case "ripple":
return new RippleDrawable();
case "color":
return new ColorDrawable();
case "shape":
return new GradientDrawable();
case "vector":
return new VectorDrawable();
case "animated-vector":
return new AnimatedVectorDrawable();
case "scale":
return new ScaleDrawable();
case "clip":
return new ClipDrawable();
case "rotate":
return new RotateDrawable();
case "animated-rotate":
return new AnimatedRotateDrawable();
case "animation-list":
return new AnimationDrawable();
case "inset":
return new InsetDrawable();
case "bitmap":
return new BitmapDrawable();
case "nine-patch":
return new NinePatchDrawable();
default:
return null;
}
android.graphics.drawable.DrawableInflater#inflateFromClass
try {
Constructor<? extends Drawable> constructor;
synchronized (CONSTRUCTOR_MAP) {
constructor = CONSTRUCTOR_MAP.get(className);
if (constructor == null) {
final Class<? extends Drawable> clazz =
mClassLoader.loadClass(className).asSubclass(Drawable.class);
constructor = clazz.getConstructor();
CONSTRUCTOR_MAP.put(className, constructor);
}
}
return constructor.newInstance();
} catch (NoSuchMethodException e) {
final InflateException ie = new InflateException(
"Error inflating class " + className);
ie.initCause(e);
throw ie;
} catch (ClassCastException e) {
// If loaded class is not a Drawable subclass.
final InflateException ie = new InflateException(
"Class is not a Drawable " + className);
ie.initCause(e);
throw ie;
} catch (ClassNotFoundException e) {
// If loadClass fails, we should propagate the exception.
final InflateException ie = new InflateException(
"Class not found " + className);
ie.initCause(e);
throw ie;
} catch (Exception e) {
final InflateException ie = new InflateException(
"Error inflating class " + className);
ie.initCause(e);
throw ie;
}
android.graphics.drawable.GradientDrawable#inflate
```
## 2.1 如何用布局加载一个ShapeDrawable
根据前面的加载流程追踪，官网所说的
>This object can be defined in an XML file with the \<shape\> element.
应该是不正确的，那我们有没有可能从资源文件加载一个ShapDrawable呢？
上面还有一个 inflateFromClass ，我们试一下。
因为最少要api 24，就移到了24的资源文件夹中。
加载后调用的android.graphics.drawable.Drawable#inflate(android.content.res.Resources, org.xmlpull.v1.XmlPullParser, android.util.AttributeSet, android.content.res.Resources.Theme)
ShapeDrawable中调用到android.graphics.drawable.ShapeDrawable#updateStateFromTypedArray
看到虽然Shape不能设置，但至少颜色、padding是可以设置的
测试了一下成功，布局文件如下：
```
<?xml version="1.0" encoding="utf-8"?>
<drawable
xmlns:android="http://schemas.android.com/apk/res/android"
class="android.graphics.drawable.ShapeDrawable"
android:color="@color/colorPrimary">
<padding
android:bottom="20dp"
android:left="10dp" />
</drawable>
```
# 0x03 为什么要有ShapeDrawable
即然ShapeDrawable不能通过shape标签创建（可以通过drawable），GradientDrawable也可以代替ShapeDrawable，为什么还要有ShapeDrawable呢？
前面我们说过，Gradient的shape只支持RECTANGLE, OVAL, LINE, RING，那么Shape的子类呢？有
```
Shape
PathShape
RectShape
ArcShape
OvalShape
RoundRectShape
```
那就试一下ArcShape
```
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val tv: TextView = findViewById<TextView>(R.id.tv)
val background: Drawable? = tv.background
background?.let {
Log.d("xx", background.javaClass.name)
if (background is ShapeDrawable) {
val arcShape: ArcShape = ArcShape(0f, 270f)
background.shape = arcShape
}
}
}
```
效果图
而且别忘了还可以继承哦。
在源码中搜索ShapeDrawable及PaintDrawable，还是找到一些使用的。
# Talk is cheap
(https://github.com/pingfangx/AndroidX/tree/demo/demo/ShapeDrawableAndGradientDrawable)
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