Drawable加载源码解析及自定义

不念不忘少年蓝@ 2023-09-27 20:49 143阅读 0赞

### 表现 ###

1.  `drawable`可以是图片文件，也可以是xml，常用于背景,`ImageView`等
2.  代码中修改背景支持直接使用id设置，也支持使用`Drawable`对象设置
3.  通常使用`context.getResourse().getDrawable(int resid)`的方式去获取Drawable对象，断点时可以发现不同的资源产生的Drawable类型不同

### 疑问 ###

1.  为何可以对一个view设置 `background`属性，设置 `drawable` 文件就可以使其能够显示一个图像
2.  当drawable设置为图片，或xml文件时，结果会变得不一样，底层是如何处理的
3.  假如当前使用了 `shape`标签，直接在标签内定义的属性，及内部定义的标签如何被解析

### 源码探索 ###

#### 从源头`getDrawable()`开始 ####

给一个View设置背景最常用的方法`view.setBackground(Drawable drawable)`一定不陌生，当我们想使用存放在drawable目录下的资源时，通常使用`context.getResourse().getDrawable(int resid)`的方式去获取，深入以下具体实现

public Drawable getDrawable(@DrawableRes int id, @Nullable Theme theme)
            throws NotFoundException {
        return getDrawableForDensity(id, 0, theme);
    }
    
    public Drawable getDrawableForDensity(@DrawableRes int id, int density, @Nullable Theme theme) {
        final TypedValue value = obtainTempTypedValue();
        try {
            // 读取configuration里的属性
            final ResourcesImpl impl = mResourcesImpl;
            impl.getValueForDensity(id, density, value, true);
            // 获取drawable
            return loadDrawable(value, id, density, theme);
        } finally {
            releaseTempTypedValue(value);
        }
    }
    Drawable loadDrawable(@NonNull TypedValue value, int id, int density, @Nullable Theme theme)
            throws NotFoundException {
        // 最终走到实现类的加载drawable方法
        return mResourcesImpl.loadDrawable(this, value, id, density, theme);
    }
    复制代码

@Nullable
    Drawable loadDrawable(@NonNull Resources wrapper, @NonNull TypedValue value, int id,
            int density, @Nullable Resources.Theme theme)
            throws NotFoundException {
    
    	...
        try {
    		...
        	// 纯色背景，看起来设置了color即可，实际上仍然还是一个ColorDrawable对象
            final boolean isColorDrawable;
            final DrawableCache caches;
            final long key;
            ...
            // 判断是否有缓存可以用，对于同配置的同一id的资源，会优先取上次解析缓存返回，省去解析流程
            // 题外话，这就是为什么drawable会有mutate()方法隔离属性，因为不同view持有的drawable是同一个对象
            if (!mPreloading && useCache) {
                final Drawable cachedDrawable = caches.getInstance(key, wrapper, theme);
                if (cachedDrawable != null) {
                    cachedDrawable.setChangingConfigurations(value.changingConfigurations);
                    return cachedDrawable;
                }
            }
            Drawable dr;
            boolean needsNewDrawableAfterCache = false;
            if (cs != null) {
                dr = cs.newDrawable(wrapper);
            } else if (isColorDrawable) {
                dr = new ColorDrawable(value.data);
            } else {
                // 创建drawable对象并加入缓存
                dr = loadDrawableForCookie(wrapper, value, id, density);
            }
            ...
            return dr;
        } catch (Exception e) {
           ...
        }
    }
    
    复制代码

#### loadDrawable ####

private Drawable loadDrawableForCookie(@NonNull Resources wrapper, @NonNull TypedValue value,
            int id, int density) {
    	...
        try {
           ...
            try {
                // 解析文件，区分文件类型1.xml 2.常规图片类型
                if (file.endsWith(".xml")) {
                    final String typeName = getResourceTypeName(id);
                    if (typeName != null && typeName.equals("color")) {
                        dr = loadColorOrXmlDrawable(wrapper, value, id, density, file);
                    } else {
                        dr = loadXmlDrawable(wrapper, value, id, density, file);
                    }
                } else {
                    final InputStream is = mAssets.openNonAsset(
                            value.assetCookie, file, AssetManager.ACCESS_STREAMING);
                    final AssetInputStream ais = (AssetInputStream) is;
                    dr = decodeImageDrawable(ais, wrapper, value);
                }
            } finally {
                stack.pop();
            }
        } catch (Exception | StackOverflowError e) {
            Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
            final NotFoundException rnf = new NotFoundException(
                    "File " + file + " from drawable resource ID #0x" + Integer.toHexString(id));
            rnf.initCause(e);
            throw rnf;
        }
    	 ...
        return dr;
    }
    
    private Drawable loadXmlDrawable(@NonNull Resources wrapper, @NonNull TypedValue value,
            int id, int density, String file)
            throws IOException, XmlPullParserException {
        try (
                XmlResourceParser rp =
                        loadXmlResourceParser(file, id, value.assetCookie, "drawable")
        ) {
            // 最终走到了Drawable的解析xml的方法内
            return Drawable.createFromXmlForDensity(wrapper, rp, density, null);
        }
    }
    复制代码

#### createFromXmlForDensity ####

public static Drawable createFromXmlForDensity(@NonNull Resources r,
            @NonNull XmlPullParser parser, int density, @Nullable Theme theme)
            throws XmlPullParserException, IOException {
       ...
    	// 调用静态方法创建drawable对象
        Drawable drawable = createFromXmlInnerForDensity(r, parser, attrs, density, theme);
    
        if (drawable == null) {
            throw new RuntimeException("Unknown initial tag: " + parser.getName());
        }
    
        return drawable;
    }
    
    static Drawable createFromXmlInnerForDensity(@NonNull Resources r,
            @NonNull XmlPullParser parser, @NonNull AttributeSet attrs, int density,
            @Nullable Theme theme) throws XmlPullParserException, IOException {
        return r.getDrawableInflater().inflateFromXmlForDensity(parser.getName(), parser, attrs,
                density, theme);
    }
    复制代码

#### inflate ####

到这一步代码已经没法在sdk中查看了，剩余的代码在sdk内，继续分析 [aospxref.com/android-13.…][aospxref.com_android-13.]

![format_png][]

可以看到实际原生也是使用的xml标签解析，不同的xml对应不同类型的drawable实现，这里基本已经包含了所有的自带drawable了

> 系统还有部分其他Drawable，不支持标签使用，常用于代码使用，比如PaintDrawable,ShapeDrawable等等

#### 标签及其实现 ####

<shape android:shape="rectangle">
        <solid android:color="@android:color/holo_blue_dark"/>
    </shape>
    复制代码

通过这种写法，可以生成一个颜色为暗蓝色的背景，那么它是如何知道我们设置的颜色，并绘制出来呢

> Android中的自定义标签一般会预先定义在`attr`文件内，根据其描述及其解析位置，可以找寻到其实现类

通过选中`android:color`属性，找到以下源码

<declare-styleable name="GradientDrawableSolid">
        
        <attr name="color" format="color" />
    </declare-styleable>
    
    复制代码

源码干脆直接说明该属性被GradientDrawable使用 基于第四部中的标签对照，确实该标签对应的实现类为GradientDrawable

#### GradientDrawable ####

当我们使用shape标签时，将会创建一个GradientDrawable对象用于绘制，那么除了attr之外，还有一些内部标签是怎么解析的呢

public void inflate(@NonNull Resources r, @NonNull XmlPullParser parser,
            @NonNull AttributeSet attrs, @Nullable Theme theme)
            throws XmlPullParserException, IOException {
        super.inflate(r, parser, attrs, theme);
    
        mGradientState.setDensity(Drawable.resolveDensity(r, 0));
    	// 自定义View使用的同款attr解析
        final TypedArray a = obtainAttributes(r, theme, attrs, R.styleable.GradientDrawable);
        updateStateFromTypedArray(a);
        a.recycle();
    	// 解析子标签
        inflateChildElements(r, parser, attrs, theme);
    
        updateLocalState(r);
    }
    private void inflateChildElements(Resources r, XmlPullParser parser, AttributeSet attrs,
            Theme theme) throws XmlPullParserException, IOException {
        TypedArray a;
        int type;
    
        final int innerDepth = parser.getDepth() + 1;
        int depth;
        while ((type=parser.next()) != XmlPullParser.END_DOCUMENT
               && ((depth=parser.getDepth()) >= innerDepth
                       || type != XmlPullParser.END_TAG)) {
            if (type != XmlPullParser.START_TAG) {
                continue;
            }
    
            if (depth > innerDepth) {
                continue;
            }
    
            String name = parser.getName();
        	// 常见的size，solid，stroke等在此解析
            if (name.equals("size")) {
                a = obtainAttributes(r, theme, attrs, R.styleable.GradientDrawableSize);
                updateGradientDrawableSize(a);
                a.recycle();
            } else if (name.equals("gradient")) {
                a = obtainAttributes(r, theme, attrs, R.styleable.GradientDrawableGradient);
                updateGradientDrawableGradient(r, a);
                a.recycle();
            } else if (name.equals("solid")) {
                a = obtainAttributes(r, theme, attrs, R.styleable.GradientDrawableSolid);
                updateGradientDrawableSolid(a);
                a.recycle();
            } else if (name.equals("stroke")) {
                a = obtainAttributes(r, theme, attrs, R.styleable.GradientDrawableStroke);
                updateGradientDrawableStroke(a);
                a.recycle();
            } else if (name.equals("corners")) {
                a = obtainAttributes(r, theme, attrs, R.styleable.DrawableCorners);
                updateDrawableCorners(a);
                a.recycle();
            } else if (name.equals("padding")) {
                a = obtainAttributes(r, theme, attrs, R.styleable.GradientDrawablePadding);
                updateGradientDrawablePadding(a);
                a.recycle();
            } else {
                Log.w("drawable", "Bad element under <shape>: " + name);
            }
        }
    }
    复制代码

#### 其它细节 ####

1.  inflate方法是在创建后最先调用的方法，部分初始化逻辑可以放在这里
2.  在通过xml创建时，存在创建失败的情况，如不存在的标签，此时会走另一个方法进行创建，提供了可扩展性

![format_png 1][]

当标签为drawable且存在class属性时，尝试使用class内容初始化，否则使用标签名初始化

#### 流程总结 ####

Yes

getDrawable

是否有缓存

取出复用

获取文件名

是否是xml文件

解析为BitmapDrawable

解析xml标签

是否是已知标签case

解析class属性或标签

new出匹配的drawable对象

inflate

attach view

view.draw

view.drawBackground

drawable.draw

### 自定义阴影drawable ###

> 原生elevation不支持所有版本，颜色修改也有版本限制
> 
> 原生elevation光源固定，导致不同屏幕位置的控件，阴影效果不完全相同

#### 定义基类 ####

public class BaseShadowDrawable extends Drawable {
    
        protected Paint paint;
        // shadow x轴偏移
        protected float shadowDx;
        // shdaowY轴偏移
        protected float shadowDy;
        // shadow模糊半径
        protected float shadowRadius;
        // shadow颜色
        protected int shadowColor;
        public BaseShadowDrawable() {
            paint = new Paint(Paint.ANTI_ALIAS_FLAG);
            paint.setColor(Color.TRANSPARENT);
        }
    
        @Override
        public void draw(@NonNull Canvas canvas) {
        }
    
        @Override
        public void setAlpha(int alpha) {
    
        }
    
        @Override
        public void setColorFilter(@Nullable ColorFilter colorFilter) {
    
        }
    
        @Override
        public int getOpacity() {
            return 0;
        }
    
        @Override
        public void inflate(@NonNull Resources r, @NonNull XmlPullParser parser, @NonNull AttributeSet attrs, @Nullable Resources.Theme theme) throws IOException, XmlPullParserException {
            super.inflate(r, parser, attrs, theme);
            TypedArray typedArray = r.obtainAttributes(attrs, R.styleable.BaseShadowDrawable);
            shadowColor = typedArray.getColor(R.styleable.BaseShadowDrawable_android_shadowColor, Color.GRAY);
            shadowRadius = typedArray.getFloat(R.styleable.BaseShadowDrawable_android_shadowRadius, 5);
            shadowDx = typedArray.getFloat(R.styleable.BaseShadowDrawable_android_shadowDx, 0);
            shadowDy = typedArray.getFloat(R.styleable.BaseShadowDrawable_android_shadowDy, 0);
            typedArray.recycle();
        }
    }
    复制代码

#### 矩形阴影实现类，可定义圆角 ####

public class RectShadowDrawable extends BaseShadowDrawable {
    
        protected int rectRadiusX;
        protected int rectRadiusY;
    
        @Override
        public void draw(@NonNull Canvas canvas) {
            paint.setShadowLayer(shadowRadius, shadowDx, shadowDy, shadowColor);
            Rect rect = getBounds();
            canvas.drawRoundRect(rect.left, rect.top, rect.right, rect.bottom, rectRadiusX, rectRadiusY, paint);
        }
    
    
        @Override
        public void inflate(@NonNull Resources r, @NonNull XmlPullParser parser, @NonNull AttributeSet attrs, @Nullable Resources.Theme theme) throws IOException, XmlPullParserException {
            super.inflate(r, parser, attrs, theme);
            TypedArray typedArray = r.obtainAttributes(attrs, R.styleable.RectShadowDrawable);
            int allRadius = typedArray.getDimensionPixelOffset(R.styleable.RectShadowDrawable_shadowRectRadius, 0);
            rectRadiusX = typedArray.getDimensionPixelOffset(R.styleable.RectShadowDrawable_shadowRectRadiusX, allRadius);
            rectRadiusY = typedArray.getDimensionPixelOffset(R.styleable.RectShadowDrawable_shadowRectRadiusY, allRadius);
            typedArray.recycle();
        }
    }
    复制代码

#### path阴影实现类,可使用vectordrawable的path ####

public class PathShadowDrawable extends BaseShadowDrawable {
    
        protected Path path;
    
        @Override
        public void draw(@NonNull Canvas canvas) {
            paint.setShadowLayer(shadowRadius, shadowDx, shadowDy, shadowColor);
            canvas.drawPath(path, paint);
        }
    
    
        @Override
        public void inflate(@NonNull Resources r, @NonNull XmlPullParser parser, @NonNull AttributeSet attrs, @Nullable Resources.Theme theme) throws IOException, XmlPullParserException {
            super.inflate(r, parser, attrs, theme);
            TypedArray typedArray = r.obtainAttributes(attrs, R.styleable.PathShadowDrawable);
            String pathStr = typedArray.getString(R.styleable.PathShadowDrawable_shadowPath);
            path = PathParser.createPathFromPathData(pathStr);
            typedArray.recycle();
        }
    
    }
    复制代码

#### 使用方式 ####

使用drawable标签+class属性自定义

<?xml version="1.0" encoding="utf-8"?>
    <drawable class="com.bt.example.RectShadowDrawable"
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:shadowColor="#2196F3"
      android:shadowDx="10"
      android:shadowDy="10"
      android:shadowRadius="20"
      app:shadowRectRadius="20px" />
    复制代码

使用自定义标签

<?xml version="1.0" encoding="utf-8"?>
    <com.bt.example.PathShadowDrawable
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:shadowColor="#2196F3"
        android:shadowDx="0"
        android:shadowDy="0"
        android:shadowRadius="5"
        app:shadowPath="M20.808,19.797C21.198,19.407 21.831,19.407 22.222,19.797L30,27.576L37.778,19.797C38.141,19.435 38.713,19.409 39.105,19.72L39.192,19.797L40.203,20.808C40.593,21.198 40.593,21.831 40.203,22.222L22.222,40.203C21.831,40.593 21.198,40.593 20.808,40.203L19.797,39.192C19.407,38.802 19.407,38.169 19.797,37.778L27.576,30L19.797,22.222C19.435,21.859 19.409,21.287 19.72,20.895L19.797,20.808ZM39.192,40.203L40.203,39.192C40.593,38.802 40.593,38.169 40.203,37.778L35.556,33.131C35.165,32.741 34.532,32.741 34.142,33.131L33.131,34.142C32.741,34.532 32.741,35.165 33.131,35.556L37.778,40.203C38.169,40.593 38.802,40.593 39.192,40.203Z" />
    复制代码

#### 效果 ####

![format_png 2][]

作者：bt  
链接：https://juejin.cn/post/7231065366881173562

[aospxref.com_android-13.]: https://link.juejin.cn?target=http%3A%2F%2Faospxref.com%2Fandroid-13.0.0_r3%2Fxref%2Fframeworks%2Fbase%2Fgraphics%2Fjava%2Fandroid%2Fgraphics%2Fdrawable%2FDrawableInflater.java%2389
[format_png]: https://img-blog.csdnimg.cn/img_convert/803b604769d622c1995ce43141c6f3a0.webp?x-oss-process=image/format,png
[format_png 1]: https://img-blog.csdnimg.cn/img_convert/f156b8fca08823100287e44fae5a40cb.webp?x-oss-process=image/format,png
[format_png 2]: https://img-blog.csdnimg.cn/img_convert/90e6b700942b334a1dcb441de65c5dee.webp?x-oss-process=image/format,png