一、Drawable
在Android系統張,圖形圖像的繪制需要在畫布上進行操作和處理,但是繪制需要了解很多細節以及可能要進行一些複雜的處理,是以系統提供了一個被稱之為Drawable的類來進行繪制處理。通過這個類可以減少我們的繪制工作和使用成本,同時系統也提供了衆多的Drawable的派生類比如單色、圖形、位圖、裁剪、動畫等等來完成一些常見的繪制需求。Drawable是一個抽象的可繪制類。他主要是提供了一個可繪制的區域bound屬性以及一個draw成員函數,不同的派生類通過重載draw函數的實作而産生不同的繪制結果。如下是Drawable的加載流程。
從Resource.getDrawable會判斷是否.xml結尾,不是的話走6,7步,如果從xml中讀取,需要
getResource.getDrawable -> ResourceImpl.loadDrawableForCookie -> Drawable.createFromXml -> drawableInflater.inflateFromXmlForDensity -> drawable.inflate(Resources r, XmlPullParser parser, AttributeSet attrs, Resources.Theme theme)
Resources的作用是将整個過程進行了封裝、同時實作了資源的緩存。是以,為了更加直白的了解加載過程,以上步驟我們可以精簡如下:
Drawable.createFromXml -> drawableInflater.inflateFromXmlForDensity -> drawable.inflate(Resources r, XmlPullParser parser, AttributeSet attrs, Resources.Theme theme)
注意:Drawable和drawable,前者是類,後者是類的執行個體,同樣drawableInflater也是類的執行個體。
二、流程分析和方法解析
Drawable.createFromXml是靜态調用,實際上整個過程是XmlPull的解析。最終,會調用到createFromXmlInnerForDensity
@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 { //通過Resources裡面的getDrawableInflater得到DrawableInflater的執行個體 return r.getDrawableInflater().inflateFromXmlForDensity(parser.getName(), parser, attrs, density, theme); }
drawableInflater.inflateFromXmlForDensity 方法用來加載Drawable資源,如果不是我們自定義的Drawable類,邏輯流程通常如下解析:
@NonNull public Drawable inflateFromXml(@NonNull String name, @NonNull XmlPullParser parser, @NonNull AttributeSet attrs, @Nullable Theme theme) throws XmlPullParserException, IOException { if (name.equals("drawable")) { //無意義的drawable name = attrs.getAttributeValue(null, "class"); if (name == null) { throw new InflateException(" tag must specify class attribute"); } } Drawable drawable = inflateFromTag(name); //解析處Drawable的執行個體 if (drawable == null) { drawable = inflateFromClass(name); } drawable.inflate(mRes, parser, attrs, theme); //得到drawable執行個體,通過drawable.inflate去實作屬性的解析 return drawable; //傳回執行個體 }
inflateFromTag源碼如下:
@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方法是如何實作的?
Drawable本身是抽象類,根據不同實作去解析屬性,我們以ShapeDrawable為例,一般的通過TypeArray解析目前節點的屬性,如果存在子元素繼續周遊。
@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(); }
三、實作自定義Drawable類的加載
通常我們說的自定義drawable是自定義xml檔案,如果實作一種可以複用并且Android系統中沒有内置的Drawable,此外實作多個布局檔案的引用,當然你可以說完全可以将代碼自定義到靜态方法中,實作多次引用也是可以,不過我們按照Android的建議,圖形化的對象盡量以xml形式呈現。
下面,我們定義一個形狀如下的Drawable:
3.1、原理分析
那麼,要實作“自定義Drawable類的加載”需求,比如要進行技術可行性分析,那我們的依據是什麼呢?
在DrawableInflater中,除了通過inflateFromTag優先解析Drawable之外,我們發現同樣提供了inflateFromClass,通過這種方式我們同樣可以得到Drawable子類的執行個體。
Drawable drawable = inflateFromTag(name); //解析處Drawable的執行個體 if (drawable == null) { drawable = inflateFromClass(name); }
inflateFromClass的實作如下:
@NonNullprivate Drawable inflateFromClass(@NonNull String className) { try { Constructor extends Drawable> constructor; synchronized (CONSTRUCTOR_MAP) { constructor = CONSTRUCTOR_MAP.get(className); if (constructor == null) { //通過ClassLoader加載Drawable類,然後轉為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執行個體 } catch (Exception e) { //省略 } return null; }
注意:我們通過ClassLoader去加載類,那麼還要注意一個事情就是混淆,混淆時我們必須注意我們自定義的Drawable類不能被混淆,否則無法加載。
-keepclassmembers class * extends android.graphics.drawable.Drawable{ public void *(android.view.View);}
3.2、代碼執行個體
[1]定義圖形
首先,我們需要定義一個Shape圖形,在Android系統中,實作圓角圓弧最好的方式是通過Path實作。
public class RadiusBorderShape extends Shape { private Path mPath; @ColorInt private int color; //邊框顔色 private float strokeWidth; //線寬 private float[] radius; //各個角的radius @ColorInt private int backgroundColor; //背景填充顔色 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
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,進而實作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相容@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); }}
這個就是我們自己定義的Drawable類,當然,自定義往往需要自定義屬性。
[3]定義drwable檔案
自定義drawble的xml檔案,安裝慣例應該在drawable資源檔案夾下,但是我們的編譯器表現的有些不友好,要求sdk版本大于24(android 7.0)才行。
從ResourcesImpl.loadDrawableForCookie加載邏輯來看,檔案加載主要通過2種方式,檔案讀取的核心代碼如下:
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); }
一般代碼實際上可以通過loadXmlResourceParser或者mAssets.openNonAsset加載,前者加載xml檔案内置資源,後者加載圖檔檔案内置資源。通過loadXmlResourceParser加載檔案,最後一個參數制定的是drawable,但是從loadXmlResourceParser源碼中并未使用第四個參數(篇幅有限,ResourcesImpl源碼自行檢視),也就是說,加載資源時并沒有對資源檔案所在目錄進行校驗。
是以說,編譯器會校驗類型,但運作時不會校驗。這樣我們可以将xml檔案放置到非drawable目錄,可以是Assets檔案夾中,同樣也可以是xml資源檔案夾下。我們這裡将定義檔案放置到xml資源目錄即可。
源碼内容如下:
<?xml version="1.0" encoding="utf-8"?>
[4]加載并使用
事實上由于編譯工具的要求sdk api大于24才可以使用,是以,我們android:background="@xml/radius_border"顯然存在問題,除非我們自行實作LayoutInfater.Factory2,通過自定義的方式去攔截和解析,但是由于篇幅問題,這裡我們通過一般代碼加載。
public class ResourceUtils { private static final HashMap> 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) { //通過ClassLoader加載Drawable類,然後轉為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執行個體 } catch (Exception e) { //省略 } return null; }}
當然,用法我們以ImageView為例
Drawable drawable = ResourceUtils.getDrawable(mContext,R.xml.radius_border);myImageView.setBackgroundDrawable(drawable);
四、總結
我們通過這種方式成功實作了自定義Drawable的加載,DrawableInflater作為加載引擎和路由,我們應該充分利用這種關系,作為Inflater,同樣LayoutInflater.Factory值得我們去實踐。