Android 經過DrawableInflater加載自定義Drawable
1、Drawable
在Android系統張，圖形圖像的繪製須要在畫布上進行操做和處理，可是繪製須要瞭解不少細節以及可能要進行一些複雜的處理，所以系統提供了一個被稱之爲Drawable的類來進行繪製處理。經過這個類能夠減小咱們的繪製工做和使用成本，同時系統也提供了衆多的Drawable的派生類好比單色、圖形、位圖、裁剪、動畫等等來完成一些常見的繪製需求。Drawable是一個抽象的可繪製類。他主要是提供了一個可繪製的區域bound屬性以及一個draw成員函數，不一樣的派生類經過重載draw函數的實現而產生不一樣的繪製結果。以下是Drawable的加載流程。java
從Resource.getDrawable會判斷是否.xml結尾，不是的話走6，7步，若是從xml中讀取，須要android
getResource.getDrawable -> ResourceImpl.loadDrawableForCookie -> Drawable.createFromXml -> drawableInflater.inflateFromXmlForDensity -> drawable.inflate(Resources r, XmlPullParser parser, AttributeSet attrs, Resources.Theme theme)git
Resources的做用是將整個過程進行了封裝、同時實現了資源的緩存。所以，爲了更加直白的瞭解加載過程，以上步驟咱們能夠精簡以下：github
Drawable.createFromXml -> drawableInflater.inflateFromXmlForDensity -> drawable.inflate(Resources r, XmlPullParser parser, AttributeSet attrs, Resources.Theme theme)canvas
注意:Drawable和drawable，前者是類，後者是類的實例，一樣drawableInflater也是類的實例。api
2、流程分析和方法解析
Drawable.createFromXml是靜態調用，實際上整個過程是XmlPull的解析。最終，會調用到createFromXmlInnerForDensity緩存
@NonNull
public static Drawable createFromXmlForDensity(@NonNull Resources r,
@NonNull XmlPullParser parser, int density, @Nullable Theme theme)
throws XmlPullParserException, IOException {
AttributeSet attrs = Xml.asAttributeSet(parser);
int type;
//noinspection StatementWithEmptyBody
while ((type=parser.next()) != XmlPullParser.START_TAG
&& type != XmlPullParser.END_DOCUMENT) {
// Empty loop.
}
if (type != XmlPullParser.START_TAG) {
throw new XmlPullParserException("No start tag found");
}
Drawable drawable = createFromXmlInnerForDensity(r, parser, attrs, density, theme);
if (drawable == null) {
throw new RuntimeException("Unknown initial tag: " + parser.getName());
}
return drawable;
}
@NonNull
static Drawable createFromXmlInnerForDensity(@NonNull Resources r,
@NonNull XmlPullParser parser, @NonNull AttributeSet attrs, int density,
@Nullable Theme theme) throws XmlPullParserException, IOException {
//經過Resources裏面的getDrawableInflater獲得DrawableInflater的實例
return r.getDrawableInflater().inflateFromXmlForDensity(parser.getName(), parser, attrs,
density, theme);
}
drawableInflater.inflateFromXmlForDensity 方法用來加載Drawable資源，若是不是咱們自定義的Drawable類，邏輯流程一般以下解析：app
@NonNull
public Drawable inflateFromXml(@NonNull String name, @NonNull XmlPullParser parser,
@NonNull AttributeSet attrs, @Nullable Theme theme)
throws XmlPullParserException, IOException {
if (name.equals("drawable")) { //無心義的drawable
name = attrs.getAttributeValue(null, "class");
if (name == null) {
throw new InflateException("<drawable> tag must specify class attribute");
}
}
Drawable drawable = inflateFromTag(name); //解析處Drawable的實例
if (drawable == null) {
drawable = inflateFromClass(name);
}
drawable.inflate(mRes, parser, attrs, theme);
//獲得drawable實例，經過drawable.inflate去實現屬性的解析
return drawable; //返回實例
}
inflateFromTag源碼以下：ide
@NonNull
@SuppressWarnings("deprecation")
private Drawable inflateFromTag(@NonNull String name) {
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;
}
}
那麼drawable.inflate方法是如何實現的？函數
Drawable自己是抽象類，根據不一樣實現去解析屬性，咱們以ShapeDrawable爲例，通常的經過TypeArray解析當前節點的屬性，若是存在子元素繼續遍歷。
@Override
public void inflate(Resources r, XmlPullParser parser, AttributeSet attrs, Theme theme)
throws XmlPullParserException, IOException {
super.inflate(r, parser, attrs, theme);
final TypedArray a = obtainAttributes(r, theme, attrs, R.styleable.ShapeDrawable);
updateStateFromTypedArray(a);
a.recycle();
int type;
final int outerDepth = parser.getDepth();
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > outerDepth)) {
if (type != XmlPullParser.START_TAG) {
continue;
}
final String name = parser.getName();
// 解析子節點
if (!inflateTag(name, r, parser, attrs)) {
android.util.Log.w("drawable", "Unknown element: " + name +
" for ShapeDrawable " + this);
}
}
// Update local properties.
updateLocalState();
}
3、實現自定義Drawable類的加載
一般咱們說的自定義drawable是自定義xml文件，若是實現一種能夠複用而且Android系統中沒有內置的Drawable，此外實現多個佈局文件的引用，固然你能夠說徹底能夠將代碼自定義到靜態方法中，實現屢次引用也是能夠，不過咱們按照Android的建議，圖形化的對象儘可能以xml形式呈現。
下面，咱們定義一個形狀以下的Drawable：
3.一、原理分析
那麼，要實現「自定義Drawable類的加載」需求，好比要進行技術可行性分析，那咱們的依據是什麼呢？
在DrawableInflater中，除了經過inflateFromTag優先解析Drawable以外，咱們發現一樣提供了inflateFromClass，經過這種方式咱們一樣能夠獲得Drawable子類的實例。
Drawable drawable = inflateFromTag(name); //解析處Drawable的實例
if (drawable == null) {
drawable = inflateFromClass(name);
}
inflateFromClass的實現以下：
@NonNull
private Drawable inflateFromClass(@NonNull String className) {
try {
Constructor<? extends Drawable> constructor;
synchronized (CONSTRUCTOR_MAP) {
constructor = CONSTRUCTOR_MAP.get(className);
if (constructor == null) {
//經過ClassLoader加載Drawable類，而後轉爲Drawable類
final Class<? extends Drawable> clazz =
mClassLoader.loadClass(className).asSubclass(Drawable.class);
constructor = clazz.getConstructor();
CONSTRUCTOR_MAP.put(className, constructor);
}
}
return constructor.newInstance(); //建立Drawable實例
} catch (Exception e) {
//省略
}
return null;
}
注意：咱們經過ClassLoader去加載類，那麼還要注意一個事情就是混淆，混淆時咱們必須注意咱們自定義的Drawable類不能被混淆，不然沒法加載。
-keepclassmembers class * extends android.graphics.drawable.Drawable{
public void *(android.view.View);
}
3.二、代碼實例
[1]定義圖形
首先，咱們須要定義一個Shape圖形，在Android系統中，實現圓角圓弧最好的方式是經過Path實現。
public class RadiusBorderShape extends Shape {
private Path mPath;
@ColorInt
private int color; //邊框顏色
private float strokeWidth; //線寬
private float[] radius; //各個角的radius
@ColorInt
private int backgroundColor; //背景填充顏色
public void setColor(@ColorInt int color) {
this.color = color;
}
public void setRadius(float[] radius) {
if(radius==null || radius.length<4){
this.radius = new float[4];
}else{
this.radius = radius;
}
for (int i=0;i<this.radius.length;i++){
float v = this.radius[i];
if(v<0) {
this.radius[i] = 0f;
}
}
}
public void setStrokeWidth(float strokeWidth) {
if(strokeWidth<0) {
strokeWidth = 0;
}
this.strokeWidth = strokeWidth;
}
public RadiusBorderShape(){
mPath = new Path();
this.strokeWidth = 5f;
this.color = Color.RED;
this.backgroundColor = Color.GREEN;
this.radius = new float[]{5f,0f,20f,30f};
}
@Override
public void draw(Canvas canvas, Paint paint) {
Paint.Style old_style = paint.getStyle();
int old_color = paint.getColor();
float old_strokeWidth = paint.getStrokeWidth();
paint.setStrokeWidth(this.strokeWidth);
int backgroundId = canvas.save();
canvas.translate(strokeWidth,strokeWidth);
drawBackground(canvas, paint);
drawBorder(canvas, paint);
canvas.restoreToCount(backgroundId);
paint.setStyle(old_style);
paint.setColor(old_color);
paint.setStrokeWidth(old_strokeWidth);
}
private void drawBorder(Canvas canvas, Paint paint) {
paint.setStyle(Paint.Style.STROKE);
paint.setColor(this.color);
canvas.scale(1, 1);
canvas.drawPath(mPath, paint);
}
private void drawBackground(Canvas canvas, Paint paint) {
final Path.FillType fillType = mPath.getFillType();
int borderId = canvas.save();
paint.setStyle(Paint.Style.FILL);
paint.setColor(this.backgroundColor);
if(this.backgroundColor!=Color.TRANSPARENT){
mPath.setFillType(Path.FillType.WINDING); //填充，兼容低版本沒法填充的問題
}
canvas.drawPath(mPath, paint);
canvas.restoreToCount(borderId);
mPath.setFillType(fillType);//還原
}
@Override
protected void onResize(float width, float height) {
super.onResize(width, height);
float w = width - strokeWidth*2; //減去左右側的線寬
float h = height - strokeWidth*2; //減去上下側的線寬
mPath.reset();
if(w<=0 && h<=0){
return;
}
float leftTopThresold = radius[0];
mPath.moveTo(0,leftTopThresold);
//從180度處順時針旋轉，增量90度
mPath.arcTo(new RectF(0,0,leftTopThresold,leftTopThresold), 180f, 90f);
float rightTopThresold = radius[1];
mPath.lineTo(w-rightTopThresold,0);
mPath.arcTo(new RectF(w-rightTopThresold,0,w,rightTopThresold), 270f, 90f);
float rightBottomThresold = radius[2];
mPath.lineTo(w,h-rightBottomThresold);
mPath.arcTo(new RectF(w-rightBottomThresold,h-rightBottomThresold,w,h), 0f, 90f);
float leftBottomThresold = radius[3];
mPath.lineTo(leftBottomThresold,h);
mPath.arcTo(new RectF(0,h-leftBottomThresold,leftBottomThresold,h), 90f, 90f);
mPath.lineTo(0,leftTopThresold);
mPath.close();
}
@Override
public Shape clone() throws CloneNotSupportedException {
final RadiusBorderShape shape = (RadiusBorderShape) super.clone();
shape.mPath = new Path(mPath);
shape.radius = radius;
shape.strokeWidth = strokeWidth;
shape.color = color;
return shape;
}
public void setBackgroundColor(int backgroundColor) {
this.backgroundColor = backgroundColor;
}
}
在這個類中，最終要的2個方法是onResize和draw方法，shape.onResize在Drawable中會被drawable.onBoundsChanged調用，從而實現Drawable大小的監聽。
[2]定義Drawable
public class RadiusRectDrawable extends ShapeDrawable {
private int backgroundColor;
private RadiusBorderShape shape;
@Override
public void inflate(Resources r, XmlPullParser parser, AttributeSet attrs, Resources.Theme theme) throws XmlPullParserException, IOException {
TypedArray array = RadiusRectDrawable.obtainAttributes(r, theme, attrs, R.styleable.RadiusRectDrawable);
if(array==null) return;
backgroundColor = array.getColor(R.styleable.RadiusRectDrawable_backgroundColor, Color.TRANSPARENT);
array.recycle();
super.inflate(r, parser, attrs, theme);
}
//低版本api兼容
@Override
public void inflate(@NonNull Resources r, @NonNull XmlPullParser parser, @NonNull AttributeSet attrs) throws XmlPullParserException, IOException {
TypedArray array = RadiusRectDrawable.obtainAttributes(r, null, attrs, R.styleable.RadiusRectDrawable);
if(array==null) return;
backgroundColor = array.getColor(R.styleable.RadiusRectDrawable_backgroundColor, Color.TRANSPARENT);
array.recycle();
super.inflate(r, parser, attrs);
}
@Override
protected boolean inflateTag(String name, Resources r, XmlPullParser parser, AttributeSet attrs) {
if("RadiusBorderShape".equals(name)){
TypedArray array = r.obtainAttributes(attrs, R.styleable.RadiusRectDrawable);
int lineColor = array.getColor(R.styleable.RadiusRectDrawable_lineColor, Color.TRANSPARENT);
float lineWidth = array.getFloat(R.styleable.RadiusRectDrawable_lineWidth, 0f);
float leftTopRadius = array.getDimensionPixelSize(R.styleable.RadiusRectDrawable_leftTop_radius, 0);
float leftBottomRadius = array.getDimensionPixelSize(R.styleable.RadiusRectDrawable_leftBottom_radius, 0);
float rightTopRadius = array.getDimensionPixelSize(R.styleable.RadiusRectDrawable_rightTop_radius, 0);
float rightBottomRadius = array.getDimensionPixelSize(R.styleable.RadiusRectDrawable_rightBottom_radius, 0);
if(shape==null){
shape = new RadiusBorderShape();
}
shape.setColor(lineColor);
shape.setStrokeWidth(lineWidth);
shape.setRadius(new float[]{leftTopRadius,rightTopRadius,rightBottomRadius,leftBottomRadius});
shape.setBackgroundColor(backgroundColor);
if(shape!=getShape()){
setShape(shape);
}
array.recycle();
return true;
}
else{
return super.inflateTag(name, r, parser, attrs);
}
}
protected static @NonNull TypedArray obtainAttributes(@NonNull Resources res,
@Nullable Resources.Theme theme, @NonNull AttributeSet set, @NonNull int[] attrs) {
if (theme == null) {
return res.obtainAttributes(set, attrs);
}
return theme.obtainStyledAttributes(set, attrs, 0, 0);
}
}
這個就是咱們本身定義的Drawable類，固然，自定義每每須要自定義屬性。
<declare-styleable name="RadiusRectDrawable">
<attr name="lineColor" format="color|reference"/>
<attr name="backgroundColor" format="color|reference"/>
<attr name="lineWidth" format="float|reference"/>
<attr name="leftTop_radius" format="dimension|reference" />
<attr name="leftBottom_radius" format="dimension|reference" />
<attr name="rightBottom_radius" format="dimension|reference" />
<attr name="rightTop_radius" format="dimension|reference" />
</declare-styleable>
[3]定義drwable文件
自定義drawble的xml文件，安裝慣例應該在drawable資源文件夾下，可是咱們的編譯器表現的有些不友好，要求sdk版本大於24（android 7.0)才行。
從ResourcesImpl.loadDrawableForCookie加載邏輯來看，文件加載主要經過2種方式，文件讀取的核心代碼以下：
if (file.endsWith(".xml")) {
final XmlResourceParser rp = loadXmlResourceParser(
file, id, value.assetCookie, "drawable");
dr = Drawable.createFromXmlForDensity(wrapper, rp, density, null);
rp.close();
} else {
final InputStream is = mAssets.openNonAsset(
value.assetCookie, file, AssetManager.ACCESS_STREAMING);
AssetInputStream ais = (AssetInputStream) is;
dr = decodeImageDrawable(ais, wrapper, value);
}
通常代碼實際上能夠經過loadXmlResourceParser或者mAssets.openNonAsset加載，前者加載xml文件內置資源，後者加載圖片文件內置資源。經過loadXmlResourceParser加載文件，最後一個參數制定的是drawable，可是從loadXmlResourceParser源碼中並未使用第四個參數（篇幅有限，ResourcesImpl源碼自行查看），也就是說，加載資源時並無對資源文件所在目錄進行校驗。
所以說，編譯器會校驗類型，但運行時不會校驗。這樣咱們能夠將xml文件放置到非drawable目錄，能夠是Assets文件夾中，一樣也能夠是xml資源文件夾下。咱們這裏將定義文件放置到xml資源目錄便可。
源碼內容以下：
<?xml version="1.0" encoding="utf-8"?>
<com.example.cc.myapplication.shape.RadiusRectDrawable
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
app:backgroundColor="@color/white"
>
<RadiusBorderShape
app:lineColor="@color/colorAccent"
app:lineWidth="5.5"
app:leftTop_radius="50dip"
app:leftBottom_radius="0dip"
app:rightTop_radius="0dip"
app:rightBottom_radius="0dip"
/>
</com.example.cc.myapplication.shape.RadiusRectDrawable>
[4]加載並使用
事實上因爲編譯工具的要求sdk api大於24纔可使用，所以，咱們android:background="@xml/radius_border"顯然存在問題，除非咱們自行實現LayoutInfater.Factory2，經過自定義的方式去攔截和解析，可是因爲篇幅問題，這裏咱們經過通常代碼加載。
public class ResourceUtils {
private static final HashMap<String, Constructor<? extends Drawable>> CONSTRUCTOR_MAP =
new HashMap<>();
private Context context;
private ResourceUtils(Context context){
this.context = context;
}
public Context getContext() {
return context;
}
//加載drawable
public static Drawable getDrawable(Context context, int xmlShapeId){
try {
ResourceUtils resourceUtils = new ResourceUtils(context);
return resourceUtils.parseDrawable(xmlShapeId);
}catch (Exception e){
e.printStackTrace();
}
return null;
}
private Drawable parseDrawable(int xmlId) { //R.xml.radius_border)
Drawable drawable = null;
try{
if(Build.VERSION.SDK_INT<24) {
drawable = parseDrawableFromClass(xmlId);
}
if(drawable!=null){
return drawable;
}
Context context = getContext();
Resources resources = context.getResources();
XmlResourceParser xmlParse = resources.getXml(xmlId);
if(Build.VERSION.SDK_INT>=21) {
drawable = Drawable.createFromXml(resources, xmlParse, context.getTheme());
}else{
drawable = Drawable.createFromXml(resources, xmlParse);
}
xmlParse.close();
}catch (Exception e){
e.printStackTrace();
}
return drawable;
}
private Drawable parseDrawableFromClass(int xmlId){
Drawable drawable = null;
try {
Context context = getContext();
Resources resources = context.getResources();
XmlResourceParser xmlParse = resources.getXml(xmlId);
AttributeSet attrs = Xml.asAttributeSet(xmlParse);
int type;
while ((type = xmlParse.next()) != XmlPullParser.START_TAG
&& type != XmlPullParser.END_DOCUMENT) {
}
if (type != XmlPullParser.START_TAG) {
throw new XmlPullParserException("No start tag found");
}
drawable = inflateFromClass(xmlParse.getName());
if(drawable==null) return null;
if (Build.VERSION.SDK_INT >= 21) {
drawable.inflate(resources, xmlParse, attrs, context.getTheme());
} else {
drawable.inflate(resources, xmlParse, attrs);
}
}catch (Exception e){
e.printStackTrace();
}
return drawable;
}
@NonNull
private Drawable inflateFromClass(@NonNull String className) {
try {
Constructor<? extends Drawable> constructor;
synchronized (CONSTRUCTOR_MAP) {
constructor = CONSTRUCTOR_MAP.get(className);
if (constructor == null) {
//經過ClassLoader加載Drawable類，而後轉爲Drawable類
final Class<? extends Drawable> clazz =
getClass().getClassLoader().loadClass(className).asSubclass(Drawable.class);
constructor = clazz.getConstructor();
CONSTRUCTOR_MAP.put(className, constructor);
}
}
return constructor.newInstance(); //建立Drawable實例
} catch (Exception e) {
//省略
}
return null;
}
}
固然，用法咱們以ImageView爲例
Drawable drawable = ResourceUtils.getDrawable(mContext,R.xml.radius_border); myImageView.setBackgroundDrawable(drawable);
4、總結
咱們經過這種方式成功實現了自定義Drawable的加載，DrawableInflater做爲加載引擎和路由，咱們應該充分利用這種關係，做爲Inflater，一樣LayoutInflater.Factory值得咱們去實踐。
附錄：
1）LayoutInflater.Factory2加載機制請參閱以下連接：
https://my.oschina.net/ososchina/blog/405904
2）DrawableInflater請參閱以下連接：
https://github.com/aosp-mirror/platform_frameworks_base/blob/master/graphics/java/android/graphics/drawable/DrawableInflater.java
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