包体积：Layout 二进制文件裁剪优化

val attributeCount = attrs.attributeCount
for (i in 0 until attributeCount) {
    val result = attrs.getAttributeValue(i)
    val name = attrs.getAttributeName(i)
    println("name:$name ,value::::$result")
}

最终就会调用到 XmlResourceParser 中的方法，最终调用到 Native 中。

public FrameLayout(@NonNull Context context, @Nullable AttributeSet attrs,
        @AttrRes int defStyleAttr, @StyleRes int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);


    final TypedArray a = context.obtainStyledAttributes(
            attrs, R.styleable.FrameLayout, defStyleAttr, defStyleRes);
    saveAttributeDataForStyleable(context, R.styleable.FrameLayout,
            attrs, a, defStyleAttr, defStyleRes);


    if (a.getBoolean(R.styleable.FrameLayout_measureAllChildren, false)) {
        setMeasureAllChildren(true);
    }


    a.recycle();
}

//https://android.googlesource.com/platform/frameworks/base/+/6d0e2c9cb948a10137e6b5a4eb00e601622fe8ee/core/jni/android_util_AssetManager.cpp
static jboolean android_content_AssetManager_applyStyle(JNIEnv* env, jobject clazz,
                                                        jlong themeToken,
                                                        jint defStyleAttr,
                                                        jint defStyleRes,
                                                        jlong xmlParserToken,
                                                        jintArray attrs,
                                                        jintArray outValues,
                                                        jintArray outIndices)
{
...
        const jsize xmlAttrIdx = xmlAttrFinder.find(curIdent);
        if (xmlAttrIdx != xmlAttrEnd) {
            // We found the attribute we were looking for.
            block = kXmlBlock;
            xmlParser->getAttributeValue(xmlAttrIdx, &value);
            DEBUG_STYLES(ALOGI("-> From XML: type=0x%x, data=0x%08x",
                    value.dataType, value.data));
        }
...


}


//https://android.googlesource.com/platform/frameworks/base/+/6d0e2c9cb948a10137e6b5a4eb00e601622fe8ee/libs/androidfw/ResourceTypes.cpp
ssize_t ResXMLParser::getAttributeValue(size_t idx, Res_value* outValue) const
{
    if (mEventCode == START_TAG) {
        const ResXMLTree_attrExt* tag = (const ResXMLTree_attrExt*)mCurExt;
        if (idx < dtohs(tag->attributeCount)) {
            const ResXMLTree_attribute* attr = (const ResXMLTree_attribute*)
                (((const uint8_t*)tag)
                 + dtohs(tag->attributeStart)
                 + (dtohs(tag->attributeSize)*idx));
            outValue->copyFrom_dtoh(attr->typedValue);
            if (mTree.mDynamicRefTable != NULL &&
                    mTree.mDynamicRefTable->lookupResourceValue(outValue) != NO_ERROR) {
                return BAD_TYPE;
            }
            return sizeof(Res_value);
        }
    }
    return BAD_TYPE;
}

protected Chunk(ByteBuffer buffer, @Nullable Chunk parent) {
  this.parent = parent;
  offset = buffer.position() - 2;
  headerSize = (buffer.getShort() & 0xFFFF);
  chunkSize = buffer.getInt();
}


//StringPoolChunk
protected StringPoolChunk(ByteBuffer buffer, @Nullable Chunk parent) {
  super(buffer, parent);
  stringCount = buffer.getInt();
  styleCount = buffer.getInt();
  flags        = buffer.getInt();
  stringsStart = buffer.getInt();
  stylesStart  = buffer.getInt();
}


// StringPoolChunk
@Override
protected void init(ByteBuffer buffer) {
  super.init(buffer);
  strings.addAll(readStrings(buffer, offset + stringsStart, stringCount));
  styles.addAll(readStyles(buffer, offset + stylesStart, styleCount));
}




private List<String> readStrings(ByteBuffer buffer, int offset, int count) {
  List<String> result = new ArrayList<>();
  int previousOffset = -1;
  // After the header, we now have an array of offsets for the strings in this pool.
  for (int i = 0; i < count; ++i) {
    int stringOffset = offset + buffer.getInt();
    result.add(ResourceString.decodeString(buffer, stringOffset, getStringType()));
    if (stringOffset <= previousOffset) {
      isOriginalDeduped = true;
    }
    previousOffset = stringOffset;
  }
  return result;
}


public static String decodeString(ByteBuffer buffer, int offset, Type type) {
  int length;
  int characterCount = decodeLength(buffer, offset, type);
  offset += computeLengthOffset(characterCount, type);
  // UTF-8 strings have 2 lengths: the number of characters, and then the encoding length.
  // UTF-16 strings, however, only have 1 length: the number of characters.
  if (type == Type.UTF8) {
    length = decodeLength(buffer, offset, type);
    offset += computeLengthOffset(length, type);
  } else {
    length = characterCount * 2;
  }
  return new String(buffer.array(), offset, length, type.charset());
}

ResourceMap封装过程：

private List<Integer> enumerateResources(ByteBuffer buffer) {
  // id 固定为 4 个字节
  int resourceCount = (getOriginalChunkSize() - getHeaderSize()) / RESOURCE_SIZE; 
  List<Integer> result = new ArrayList<>(resourceCount);
  int offset = this.offset + getHeaderSize();
  buffer.mark();
  buffer.position(offset);


  for (int i = 0; i < resourceCount; ++i) {
    result.add(buffer.getInt());
  }


  buffer.reset();
  return result;
}

protected XmlStartElementChunk(ByteBuffer buffer, @Nullable Chunk parent) {
  super(buffer, parent);
  // 获取namespace的id
  namespace = buffer.getInt();
  // 获取名称
  name = buffer.getInt();
  // 获取属性索引的开始位置
  attributeStart = (buffer.getShort() & 0xFFFF);
  // 获取索引的总大小
  int attributeSize = (buffer.getShort() & 0xFFFF);
  // 强制检查 attributeSize 的值是否为固定值，
  Preconditions.checkState(attributeSize == XmlAttribute.SIZE, // 20 
      "attributeSize is wrong size. Got %s, want %s", attributeSize, XmlAttribute.SIZE);
  attributeCount = (buffer.getShort() & 0xFFFF);


  // The following indices are 1-based and need to be adjusted.
  idIndex = (buffer.getShort() & 0xFFFF) - 1;
  classIndex = (buffer.getShort() & 0xFFFF) - 1;
  styleIndex = (buffer.getShort() & 0xFFFF) - 1;
}


private List<XmlAttribute> enumerateAttributes(ByteBuffer buffer) {
  List<XmlAttribute> result = new ArrayList<>(attributeCount);
  int offset = this.offset + getHeaderSize() + attributeStart;
  int endOffset = offset + XmlAttribute.SIZE * attributeCount;
  buffer.mark();
  buffer.position(offset);


  while (offset < endOffset) {
    result.add(XmlAttribute.create(buffer, this));
    offset += XmlAttribute.SIZE;
  }


  buffer.reset();
  return result;
}

/**
 * Creates a new {@link XmlAttribute} based on the bytes at the current {@code buffer} position.
 *
 * @param buffer A buffer whose position is at the start of a {@link XmlAttribute}.
 * @param parent The parent chunk that contains this attribute; used for string lookups.
 */
public static XmlAttribute create(ByteBuffer buffer, XmlNodeChunk parent) {
  int namespace = buffer.getInt(); // 4
  int name = buffer.getInt(); // 4
  int rawValue = buffer.getInt(); // 4
  ResourceValue typedValue = ResourceValue.create(buffer);
  return new AutoValue_XmlAttribute(namespace, name, rawValue, typedValue, parent);
}




public static ResourceValue create(ByteBuffer buffer) {
  int size = (buffer.getShort() & 0xFFFF); //2
  buffer.get();  // Unused // Always set to 0. 1  
  Type type = Type.fromCode(buffer.get());//1
  int data = buffer.getInt(); // 4
  return new AutoValue_ResourceValue(size, type, data);
}

<string name="spannable_string">
  This is a <b>bold</b> text, this is an <i>italic</i>
</string>

FileInputStream(resourcesFile).use { inputStream ->
    val resouce = ResourceFile.fromInputStream(inputStream)
    val chunks = sChunk.chunks
    // 过滤出所有的 NameSpaceChunk 对象
    val result = chunks.values.filter { it is XmlNamespaceChunk }
    // 移除
    chunks.values.removeAll(result.toSet())


}

private fun handleStringPoolValue(strings: MutableList<String>, resources: MutableList<Int>?, stringPoolChunk: StringPoolChunk, emptyIndexs: MutableList<Int>) {
    strings.forEachIndexed { i, k ->
        val res = resources
        // 默认属性置空
        if (res != null && i < res.size) {
            stringPoolChunk.setString(i, "")
            emptyIndexs.add(i)
        }
        // 命名空间置空
        else if (k == "http://schemas.android.com/apk/res/android") {
            stringPoolChunk.setString(i, "")
            emptyIndexs.add(i)
        } else if (k == "http://schemas.android.com/apk/res-auto") {
            stringPoolChunk.setString(i, "")
            emptyIndexs.add(i)
        } else if (k == "http://schemas.android.com/tools") {
            stringPoolChunk.setString(i, "")
            emptyIndexs.add(i)
        } else if (k == "android") {
            stringPoolChunk.setString(i, "")
            emptyIndexs.add(i)
        } else if (k == "app") {
            stringPoolChunk.setString(i, "")
            emptyIndexs.add(i)
        } else if (k == "tools") {
            stringPoolChunk.setString(i, "")
            emptyIndexs.add(i)
        }
    }
}

FileOutputStream(resourcesFile).use {
    it.write(newResouce.toByteArray(true))
}


@Override
public byte[] toByteArray(boolean shrink) throws IOException {
  ByteArrayDataOutput output = ByteStreams.newDataOutput();
  for (Chunk chunk : chunks) {
    output.write(chunk.toByteArray(shrink));
  }
  return output.toByteArray();
}

//StringPoolChunk 中的具体写入实现
@Override
protected void writePayload(DataOutput output, ByteBuffer header, boolean shrink)
    throws IOException {
  ByteArrayOutputStream baos = new ByteArrayOutputStream();
  int stringOffset = 0;
  ByteBuffer offsets = ByteBuffer.allocate(getOffsetSize());
  offsets.order(ByteOrder.LITTLE_ENDIAN);


  // Write to a temporary payload so we can rearrange this and put the offsets first
  try (LittleEndianDataOutputStream payload = new LittleEndianDataOutputStream(baos)) {
    stringOffset = writeStrings(payload, offsets, shrink);
    writeStyles(payload, offsets, shrink);
  }


  output.write(offsets.array());
  output.write(baos.toByteArray());
  if (!styles.isEmpty()) {
    header.putInt(STYLE_START_OFFSET, getHeaderSize() + getOffsetSize() + stringOffset);
  }
}




private int writeStrings(DataOutput payload, ByteBuffer offsets, boolean shrink)
    throws IOException {
  int stringOffset = 0;
  Map<String, Integer> used = new HashMap<>();  // Keeps track of strings already written
  for (String string : strings) {
    // Dedupe everything except stylized strings, unless shrink is true (then dedupe everything)
    if (used.containsKey(string) && (shrink || isOriginalDeduped)) {
      // 如果支持优化，将复用之前的数据和 offest
      Integer offset = used.get(string);
      offsets.putInt(offset == null ? 0 : offset);
    } else {
      byte[] encodedString = ResourceString.encodeString(string, getStringType());
      payload.write(encodedString);
      used.put(string, stringOffset);
      offsets.putInt(stringOffset);
      stringOffset += encodedString.length;
    }
  }

int[] systemAttrs = {android.R.attr.layout_height};
TypedArray a = context.obtainStyledAttributes(attrs, systemAttrs);
try {
    // 如果定义的是 WRAP_CONTENT 或者 MATCH_PARENT 这里会异常，然后通过 getInt 获取值（-1 -2）
    mHeight = a.getDimensionPixelSize(0, ViewGroup.LayoutParams.WRAP_CONTENT);
} catch (Exception e) {
    // e.printStackTrace();
    mHeight = a.getInt(0, ViewGroup.LayoutParams.WRAP_CONTENT);
}

try {
    val a = context.obtainStyledAttributes(attrs, intArrayOf(android.R.attr.src))
    if (a.hasValue(0)) {
        val drawable = a.getDrawable(0)
        load(drawable)
    }
    a.recycle()
} catch (e: Exception) {
    e.printStackTrace()
}

if (attrs != null) {
    TypedArray a = context.obtainStyledAttributes(attrs, new int[]{android.R.attr.theme});
    if (a.hasValue(0)) {
        int[] attr = new int[]{R.attr.colorControlNormal, android.R.attr.textColorPrimary};
        TypedArray array = context.obtainStyledAttributes(attrs.getAttributeResourceValue(0, 0), attr);
        try {
            mNavigationIconTintColor = array.getColor(0, Color.BLACK);
            mTitleTextColor = array.getColor(1, Color.BLACK);
        } finally {
            array.recycle();
        }
    }
    a.recycle();
}

<androidx.appcompat.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    app:layout_collapseMode="pin"
    app:popupTheme="@style/ThemeToolbarWhite"
    app:theme="@style/ThemeToolbarWhite">
<androidx.appcompat.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:theme="@style/ThemeToolbarWhite"
    app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
    app:title="领取数字藏品"
    app:titleTextColor="@android:color/white" />

TypedArray a = context.obtainStyledAttributes(attrs, new int[]{R.attr.theme, android.R.attr.theme});