0xA04 Android 10 源码分析：Apk加载流程之资源加载（二）

// 根据元素名解析，生成对应的view
final View view = createViewFromTag(parent, name, context, attrs);
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
// rInflateChildren方法内部调用的rInflate方法，深度优先遍历解析所有的子view
rInflateChildren(parser, view, attrs, true);
// 添加解析的view
viewGroup.addView(view, params);

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // 设置视图大小为0
    setMeasuredDimension(0, 0);
}

...
try {
    // 利用构造函数，创建View
    final View view = constructor.newInstance(args);
    if (view instanceof ViewStub) {
        // 如果是ViewStub，则设置LayoutInflater
        final ViewStub viewStub = (ViewStub) view;
        viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
    }
    return view;
} finally {
    mConstructorArgs[0] = lastContext;
}
...

public ViewStub(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context);
    final TypedArray a = context.obtainStyledAttributes(attrs,
            R.styleable.ViewStub, defStyleAttr, defStyleRes);
    saveAttributeDataForStyleable(context, R.styleable.ViewStub, attrs, a, defStyleAttr,
            defStyleRes);
    // 解析xml中设置的 android:inflatedId 的属性
    mInflatedId = a.getResourceId(R.styleable.ViewStub_inflatedId, NO_ID);
    // 解析xml中设置的 android:layout 属性
    mLayoutResource = a.getResourceId(R.styleable.ViewStub_layout, 0);
    // 解析xml中设置的 android:id 属性
    mID = a.getResourceId(R.styleable.ViewStub_id, NO_ID);
    a.recycle();
    // view不可见
    setVisibility(GONE);
    // 不会调用 onDraw 方法绘制内容
    setWillNotDraw(true);
}

@Override
public void setVisibility(int visibility) {
    if (mInflatedViewRef != null) {
        // mInflatedViewRef 是 WeakReference的实例，调用inflate方法时候初始化
        View view = mInflatedViewRef.get();
        if (view != null) {
            // 设置View可见
            view.setVisibility(visibility);
        } else {
            throw new IllegalStateException("setVisibility called on un-referenced view");
        }
    } else {
        super.setVisibility(visibility);
        // 当View为空且设置视图可见(VISIBLE、INVISIBLE)，调用inflate方法
        if (visibility == VISIBLE || visibility == INVISIBLE) {
            inflate();
        }
    }
}

public View inflate() {
    final ViewParent viewParent = getParent();
    if (viewParent != null && viewParent instanceof ViewGroup) {
        if (mLayoutResource != 0) {
            final ViewGroup parent = (ViewGroup) viewParent;
            // 解析布局视图
            // 返回的view是android:layout指定的布局文件最顶层的view
            final View view = inflateViewNoAdd(parent);
            // 移除ViewStub
            // 添加view到被移除的ViewStub的位置
            replaceSelfWithView(view, parent);
            // 添加view到 mInflatedViewRef 中
            mInflatedViewRef = new WeakReference<>(view);
            if (mInflateListener != null) {
                // 加载完成之后，回调onInflate 方法
                mInflateListener.onInflate(this, view);
            }
            return view;
        } else {
            // 需要在xml中设置android:layout，不是layout，否则会抛出异常
            throw new IllegalArgumentException("ViewStub must have a valid layoutResource");
        }
    } else {
        // ViewStub不能作为根布局，它需要放在ViewGroup中, 否则会抛出异常
        throw new IllegalStateException("ViewStub must have a non-null ViewGroup viewParent");
    }
}

private View inflateViewNoAdd(ViewGroup parent) {
    final LayoutInflater factory;
    // mInflater 是View被创建的时候，如果是ViewStub, 将LayoutInflater赋值给mInflater
    if (mInflater != null) {
        factory = mInflater;
    } else {
        // 如果mInflater为空，则创建LayoutInflater
        factory = LayoutInflater.from(mContext);
    }
    // 从指定的 mLayoutResource 资源中解析布局视图
    // mLayoutResource 是在xml设置的 Android:layout 指定的布局文件
    final View view = factory.inflate(mLayoutResource, parent, false);
    // mInflatedId 是在xml设置的 inflateId
    if (mInflatedId != NO_ID) {
        // 将id复制给view
        view.setId(mInflatedId);
        //注意：如果指定了mInflatedId , 被inflate的layoutView的id就是mInflatedId
    }
    return view;
}
复制代

private void replaceSelfWithView(View view, ViewGroup parent) {
    // 获取ViewStub在视图中的位置
    final int index = parent.indexOfChild(this);
    // 移除ViewStub
    // 注意：调用removeViewInLayout方法之后，调用findViewById()是找不到该ViewStub对象
    parent.removeViewInLayout(this);
    final ViewGroup.LayoutParams layoutParams = getLayoutParams();
    // 将xml中指定的 android:layout 布局文件中最顶层的View，添加到被移除的 ViewStub的位置
    if (layoutParams != null) {
        parent.addView(view, index, layoutParams);
    } else {
        parent.addView(view, index);
    }
}

throw new IllegalArgumentException("ViewStub must have a valid layoutResource");

throw new IllegalStateException("ViewStub must have a non-null ViewGroup viewParent");

// 获取ViewStub在视图中的位置
final int index = parent.indexOfChild(this);
// 移除ViewStub
// 注意：调用removeViewInLayout方法之后，调用findViewById()是找不到该ViewStub对象
parent.removeViewInLayout(this);

// mInflatedId 是在xml设置的 inflateId
if (mInflatedId != NO_ID) {
    // 将id复制给view
    view.setId(mInflatedId);
    //注意：如果指定了mInflatedId , 被inflate的layoutView的id就是mInflatedId
}

final ViewGroup.LayoutParams layoutParams = getLayoutParams();
// 将xml中指定的 android:layout 布局文件中最顶层的View 也就是根view，
// 添加到被移除的 ViewStub的位置
if (layoutParams != null) {
    parent.addView(view, index, layoutParams);
} else {
    parent.addView(view, index);
}

public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    return new AllVh(LayoutInflater
            .from(viewGroup.getContext())
            .inflate(R.layout.list_item, viewGroup, false));
}

public static LayoutInflater from(Context context) {
    // 获取系统服务 LAYOUT_INFLATER_SERVICE ，并赋值给 LayoutInflater
    // Context 是一个抽象类，真正的实现类是ContextImpl
    LayoutInflater LayoutInflater =
            (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    if (LayoutInflater == null) {
        throw new AssertionError("LayoutInflater not found.");
    }
    return LayoutInflater;
}

public Object getSystemService(String name) {
    // SystemServiceRegistry 是管理系统服务的
    // 调用getSystemService方法，通过服务名字查找对应的服务
    return SystemServiceRegistry.getSystemService(this, name);
}

public static Object getSystemService(ContextImpl ctx, String name) {
    // SYSTEM_SERVICE_FETCHERS 是一个map集合
    // 从 map 集合中取出系统服务
    ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
    return fetcher != null ? fetcher.getService(ctx) : null;
}

private static <T> void registerService(String serviceName, Class<T> serviceClass,
        ServiceFetcher<T> serviceFetcher) {
    SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
    SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
}

static {
    // 初始化加载所有的系统服务
    ...
    // 省略了很多系统服务
    registerService(Context.LAYOUT_INFLATER_SERVICE, LayoutInflater.class,
            new CachedServiceFetcher<LayoutInflater>() {
        @Override
        public LayoutInflater createService(ContextImpl ctx) {
            return new PhoneLayoutInflater(ctx.getOuterContext());
        }});
    ...
    // 省略了很多系统服务
}

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // 设置视图大小为0
    setMeasuredDimension(0, 0);
}

...
try {
    // 利用构造函数，创建View
    final View view = constructor.newInstance(args);
    if (view instanceof ViewStub) {
        // 如果是ViewStub，则设置LayoutInflater
        final ViewStub viewStub = (ViewStub) view;
        viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
    }
    return view;
} finally {
    mConstructorArgs[0] = lastContext;
}
...