頁面加載流程奠货、setcontentview與inflate過程解析優(yōu)化

頁面的加載中，必不可少的是setcontentview吱窝，如果是通過資源r.layout來進(jìn)行布局加載讥邻，那么一定繞不開inflate 資源文件。那么setcontentview中到底進(jìn)行了哪些操作癣诱？官方推出的asyncinflatelayout到底優(yōu)化哪些地方计维？哪些地方是能再進(jìn)行一次優(yōu)化的？
activity中inflate操作簡化流程圖：

image

從setcontent來看撕予，分為幾個步驟

1.將docview鲫惶，theme級別配置設(shè)置到docview和window中 
2.docview removeall所有的子view 
3.開始從xml中、view 來addview都docview中实抡；
getDelegate().setContentView();
public void setContentView(int resId) {
    ensureSubDecor();//theme設(shè)置到content,
    ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
    contentParent.removeAllViews();
    LayoutInflater.from(mContext).inflate(resId, contentParent);
   mOriginalWindowCallback.onContentChanged();
}
在ensuresubdocor方法中欠母，有值得注意的點：
private void ensureSubDecor() {
    if (!mSubDecorInstalled) {
        mSubDecor = createSubDecor(); //創(chuàng)建docview同時添加到window中；
        ...
        applyFixedSizeWindow();//contentviewtheme設(shè)置吆寨；
        ....
    }
}
關(guān)鍵點：
1.createSubDecor()創(chuàng)建docview赏淌， 判斷類型創(chuàng)建相應(yīng)的docview set到window中；

之后到xml解析和view生成的邏輯中：

inflate 調(diào)用到 android.view.LayoutInflater#inflate(int, android.view.ViewGroup)
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
    final Resources res = getContext().getResources();
    if (DEBUG) {
        Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("
                + Integer.toHexString(resource) + ")");
    }
    //從resource拿到目標(biāo)資源文件
    final XmlResourceParser parser = res.getLayout(resource);
    try {
        return inflate(parser, root, attachToRoot);
    } finally {
        parser.close();
    }
}
//從resource拿到目標(biāo)資源文件  具體解析
public XmlResourceParser getLayout(@LayoutRes int id) throws NotFoundException {
    return loadXmlResourceParser(id, "layout");
}
//指定文件的xml解析器
XmlResourceParser loadXmlResourceParser(@AnyRes int id, @NonNull String type)
        throws NotFoundException {
    final TypedValue value = obtainTempTypedValue();
    try {
        final ResourcesImpl impl = mResourcesImpl;
        impl.getValue(id, value, true);
        if (value.type == TypedValue.TYPE_STRING) {
            return impl.loadXmlResourceParser(value.string.toString(), id,
                    value.assetCookie, type);
        }
        ....報錯
    } finally {
        releaseTempTypedValue(value);
    }
}
//loadXmlResourceParser 處理類啄清； 
XmlResourceParser loadXmlResourceParser(@NonNull String file, @AnyRes int id, int assetCookie,
        @NonNull String type)
        throws NotFoundException {
    if (id != 0) {
        try {
            synchronized (mCachedXmlBlocks) {
                final int[] cachedXmlBlockCookies = mCachedXmlBlockCookies; //緩存塊為4
                final String[] cachedXmlBlockFiles = mCachedXmlBlockFiles; //緩存塊為4
                final XmlBlock[] cachedXmlBlocks = mCachedXmlBlocks;//緩存塊為4
                // 首先看是否在緩存中六水，F(xiàn)irst see if this block is in our cache.
                final int num = cachedXmlBlockFiles.length;
                for (int i = 0; i < num; i++) {
                    if (cachedXmlBlockCookies[i] == assetCookie && cachedXmlBlockFiles[i] != null
                            && cachedXmlBlockFiles[i].equals(file)) {
                        return cachedXmlBlocks[i].newParser();
                    }
                }
                //不在緩存中的，創(chuàng)建一個新塊放到下一個插槽
                // Not in the cache, create a new block and put it at the next slot in the cache.
                final XmlBlock block = mAssets.openXmlBlockAsset(assetCookie, file);
                if (block != null) {
                    final int pos = (mLastCachedXmlBlockIndex + 1) % num;//有限的塊緩存只在4塊內(nèi)進(jìn)行緩存
                    mLastCachedXmlBlockIndex = pos;
                    final XmlBlock oldBlock = cachedXmlBlocks[pos];
                    if (oldBlock != null) {
                        oldBlock.close();//釋放掉之前占位的塊辣卒；
                    }
                    cachedXmlBlockCookies[pos] = assetCookie;//緩存type
                    cachedXmlBlockFiles[pos] = file;//緩存filename
                    cachedXmlBlocks[pos] = block;  //這個地方注意一下掷贾，極限優(yōu)化中可以用到；
                    return block.newParser();//返回塊中的解析結(jié)果
                }
            }
        } catch (Exception e) {
           ...拋出錯誤
        }
    }
    ...拋出錯誤
}
//xml parser之后成為擁有start-end-attrs-name的基本數(shù)據(jù)結(jié)構(gòu)荣茫，再通過inflate轉(zhuǎn)化成view實體

//從parser中的基本數(shù)據(jù)想帅，構(gòu)建view
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
    synchronized (mConstructorArgs) {
        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
        final Context inflaterContext = mContext;
        final AttributeSet attrs = Xml.asAttributeSet(parser);
        Context lastContext = (Context) mConstructorArgs[0];
        mConstructorArgs[0] = inflaterContext;
        View result = root;

        try {
            // Look for the root node. 查找root節(jié)點
            int type;
            .....查找root節(jié)點
            final String name = parser.getName();
           
            if (TAG_MERGE.equals(name)) {
               //merge標(biāo)簽驗證是否有attachroot
                rInflate(parser, root, inflaterContext, attrs, false);
            } else {
                // Temp is the root view that was found in the xml  通過tag生成view
                final View temp = createViewFromTag(root, name, inflaterContext, attrs);
                ViewGroup.LayoutParams params = null;
                if (root != null) {
                   ...
                    params = root.generateLayoutParams(attrs);//生成params，布局參數(shù)
                    if (!attachToRoot) {
                        // Set the layout params for temp if we are not
                        // attaching. (If we are, we use addView, below)
                        temp.setLayoutParams(params);
                    }
                }
                ...
                // Inflate all children under temp against its context.
                rInflateChildren(parser, temp, attrs, true);
                ...
                // We are supposed to attach all the views we found (int temp)to root. Do that now.
                if (root != null && attachToRoot) {
                    root.addView(temp, params);
                }
                // Decide whether to return the root that was passed in or the top view found in xml.
                if (root == null || !attachToRoot) {
                    result = temp;
                }
            }
        } catch (XmlPullParserException e) {
           ....exception deal
        } finally {
            // Don't retain static reference on context.上下文中不要保留靜態(tài)引用
            mConstructorArgs[0] = lastContext;
            mConstructorArgs[1] = null;
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
        return result;
    }
}

以上的流程中啡莉，window是在activity中new出來港准，docview是根據(jù)設(shè)置的theme來進(jìn)行inflate旨剥，setcontentview res方式也是通過inflate方法；通過inflate就不可避免的走到讀取文件--->格式化解析---->反射出view實體類這幾步浅缸；
如果做極限優(yōu)化轨帜，那么我們根據(jù)inflate相應(yīng)的代碼可以得出一個優(yōu)化點，可以在子線程嘗試對xml進(jìn)行加載衩椒，只要inflate執(zhí)行到存儲到block緩存中阵谚，那么就可以再下次使用相同文件的時候加快加載速度；同時在抖音的優(yōu)化策略中烟具，有對class的提前l(fā)oad來減小主頁上加載速度的優(yōu)化梢什；
還有公司開發(fā)組另辟蹊徑，把xml 轉(zhuǎn)view的其中幾個步驟進(jìn)行優(yōu)化朝聋，例如讀取xml文件的io耗時嗡午，那么我們直接再編譯期間將xml文件讀取轉(zhuǎn)化成class文件，setcontentview變成代碼動態(tài)生成布局越過xml的讀取解析兩部分冀痕，直接到inflate的convert步驟中荔睹；

asyncinflatelayout是什么框架？其中做了哪些事能異步加載布局言蛇？
顧名思義是一個異步加載布局的框架僻他，官方出品。從源碼來看不是很重腊尚，只是一個thread inflate布局的框架吨拗，主要解決inflate中io文件操作，和反射操作阻塞主線程的問題婿斥，讓infalte在子線程進(jìn)行劝篷，成功之后回調(diào)給主線程進(jìn)行后續(xù)處理；

public AsyncLayoutInflater(@NonNull Context context) {
    mInflater = new BasicInflater(context);
    mHandler = new Handler(mHandlerCallback);
    mInflateThread = InflateThread.getInstance();
}
//構(gòu)造函數(shù)中的實體類就是整個asyncinflate核心民宿，handler進(jìn)行回調(diào)娇妓，thread負(fù)責(zé)子線程infalte，infalte負(fù)責(zé)具體加載活鹰；

可能是個輕量且優(yōu)化不是很大哈恰，不能作為kpi來進(jìn)行，所以在asyncinflate的封裝上沒有考慮得特別完善志群。從子線程未用線程池着绷，異步加載未考慮調(diào)用infalte和加載view不同類的情況，都會不太細(xì)膩有限制赖舟；

頁面加載流程、setcontentview與inflate過程解析優(yōu)化

頁面加載流程碧绞、setcontentview與inflate過程解析優(yōu)化