一、場(chǎng)景以及解決的問題

實(shí)際項(xiàng)目中，經(jīng)常會(huì)遇到，剛進(jìn)入某一個(gè)界面，需要請(qǐng)求數(shù)據(jù)顯示加載中布局，網(wǎng)絡(luò)錯(cuò)誤顯示網(wǎng)絡(luò)錯(cuò)誤布局，服務(wù)器錯(cuò)誤時(shí)顯示服務(wù)器錯(cuò)誤布局，列表數(shù)據(jù)為空時(shí)顯示空布局。
最開始的時(shí)候，會(huì)將這幾個(gè)布局全部堆積在主布局中設(shè)置為Gone，等到需要的時(shí)候再去Visible。這樣子會(huì)有以下幾個(gè)問題：

• 一次性會(huì)將所有情況下對(duì)應(yīng)的布局全部加載
• 導(dǎo)致真正的頁(yè)面布局臃腫，不利于后期維護(hù)
• 做不到按需加載或懶加載
  MultiStatusLayout支持按需加載、便于調(diào)用控制、支持?jǐn)U展至任意Layout

二、實(shí)際效果以及項(xiàng)目中配置

1.效果

demo

2.項(xiàng)目中集成配置

詳細(xì)配置以及用法，參見github

1）gradle集成

allprojects {
        repositories {
            ...
            maven { url 'https://jitpack.io' }
        }
    }
    
dependencies {
        implementation 'com.github.Walll-E.MultiStatusLayout:library:1.0.7'
        annotationProcessor 'com.github.Walll-E.MultiStatusLayout:compiler:1.0.7'
    }

2）使用

定義一個(gè)類比如MultiStatusInit ，類頂部添加注解MultiStatus，點(diǎn)擊AndroidStudio的build即可。靜靜的等待編譯完畢，雙擊shift按鈕出現(xiàn)搜索框，輸入 MultiStatus 就會(huì)檢索出來相關(guān)的類，如下配置的四個(gè)Layout：編譯生成的類如下：
MultiStatusLayout、MultiStatusConstraintLayout、MultiStatusFrameLayout、MultiStatusLinearLayout

@MultiStatus(value = {
        RelativeLayout.class, 
        ConstraintLayout.class, 
        FrameLayout.class, 
        LinearLayout.class},
        
        provider = {
                RelativeLayoutConstraintProvider.class,
                ConstraintLayoutConstraintProvider.class, 
                FrameLayoutConstraintProvider.class, 
                LinearLayoutConstraintProvider.class})
public class MultiStatusInit {
}

三、Talk is cheap，show me the code

1.項(xiàng)目結(jié)構(gòu)介紹：

Annotation：MultiStatus屬性分別是：value和provider。

• value：代表需要?jiǎng)討B(tài)生成的系統(tǒng)以及第三方Layout，例如RelativeLayout、ConstraintLayout
• provider：對(duì)應(yīng)value中Layout的約束提供類，例如RelativeLayoutConstraintProvider、ConstraintLayoutConstraintProvider這兩個(gè)由sdk內(nèi)部提供

Compiler：根據(jù) 注解MultiStatus中配置的value，provider動(dòng)態(tài)生成相應(yīng)的MultiStatusxxxxxxLayout，apt生成供外部使用的核心類

Library：核心module

• MultiStatusEvent：利用apt生成的MultiStatusxxxxxxLayout實(shí)現(xiàn)這個(gè)接口，此接口提供生成類的一些行為（showLoading、showContent、showEmpty等）
• OnReloadDataListener：網(wǎng)絡(luò)錯(cuò)誤，服務(wù)器等錯(cuò)誤時(shí)，顯示相應(yīng)布局中重試接口
• MultiStatusHelper：根據(jù)不同情況顯示相應(yīng)布局的核心類

2.MultiStatusxxxxLayout提供的屬性介紹:

3.核心代碼：

Annotation

MultiStatus代碼如下：

@Retention(RetentionPolicy.CLASS)
@Target(ElementType.TYPE)
public @interface MultiStatus {
    Class<? extends ViewGroup>[] value() default {};

    Class<? extends ViewConstraintProvider>[] provider() default {};
}

• value：繼承自ViewGroup的View，例如RelativeLayout、LinearLayout、ConstraintLayout等。
• provider：實(shí)現(xiàn)ViewConstraintProvider這個(gè)接口的類，項(xiàng)目?jī)?nèi)提供RelativeLayoutConstraintProvider，ConstraintLayoutConstraintProvider
  需要注意的是：value配置的值和provider值順序必須一致。如果不一致，可能導(dǎo)致一些不可預(yù)測(cè)的bug -.-

MultiStatusHelper

//將xml中獲取的字符串ids，解析為單個(gè)的字符串id
private void setIds(String referenceIds, int type) {
        if (referenceIds == null) return;
        int begin = 0;
        while (true) {
            int end = referenceIds.indexOf(",", begin);
            if (end == -1) {
                addId(referenceIds.substring(begin), type);
                return;
            }
            addId(referenceIds.substring(begin, end), type);
            begin = end + 1;
        }
    }
    //將單個(gè)的字符串id解析為能供系統(tǒng)識(shí)別的id
    private void addId(String idString, int type) {
        if (idString == null || mContext == null) return;
        idString = idString.trim();
        int tag = 0;
        try {
            // id.class中的id為：com.wall_e.multiStatusLayout.R.id;
            Class res = id.class;
            Field field = res.getField(idString);
            tag = field.getInt(null);
        } catch (Exception e) {
            e.printStackTrace();
        }
        //如果tag==0，證明沒有獲取到相應(yīng)的id
        if (tag == 0) {
            tag = mContext.getResources().getIdentifier(idString, "id", mContext.getPackageName());
        }
        if (tag == 0) {
            Log.d(TAG, "xml中配置的referenceIds并不能被解析，當(dāng)前的Id:" + idString);
            return;
        }
        //將解析傳來的id放入mReferenceIds 緩存起來
        if (mReferenceIds == null) {
            mReferenceIds = new ArrayMap<>();
        }
        if (mReferenceIds.containsKey(type)) {
            List<Integer> list = mReferenceIds.get(type);
            if (list != null && !list.contains(tag)) {
                list.add(tag);
            }
        } else {
            List<Integer> list = new ArrayList<>();
            list.add(tag);
            mReferenceIds.put(type, list);
        }
    }

以上代碼是將app:contentReferenceIds="actionButtonCenter,actionButtonRight,actionButtonLeft"
中的contentReferenceIds中的id字符串解析為R.id.actionButtonCenter類型，首先截取出來單個(gè)的字符串id，然后用包(com.wall_e.multiStatusLayout)下的R.id,反射獲取對(duì)應(yīng)的id，如果為0，利用mContext.getResources().getIdentifier(idString, "id", mContext.getPackageName());獲取id，如果不為0，則緩存在mReferenceIds 中以供后面的使用。

 /**
     * 加載相應(yīng)狀態(tài)的布局，并且添加至ViewGroup中
     *
     * @param index       存放布局容器的索引
     * @param layoutResId 布局資源id
     * @return 返回相應(yīng)狀態(tài)的布局
     */
      private View inflateAndAddViewInLayout(int index, int layoutResId) {
        int realIndex = mRealIndex.get(index, -1);
        View view;
        if (realIndex == -1) {
            view = ViewGroup.inflate(mContext, layoutResId, null);
            if (mViewConstraintProvider != null) {
                mViewConstraintProvider.addViewBlewTargetView(view, mTargetViewId, mParent);
            }
            realIndex = mParent.indexOfChild(view);
            if (realIndex == -1) {
                mParent.addView(view);
                realIndex = mParent.getChildCount()-1;
            }
            mRealIndex.put(index, realIndex);
        } else {
            view = mParent.getChildAt(realIndex);
        }
        return view;
    }

首先去判斷mRealIndex是否緩存過這個(gè)View在ViewGroup中的索引，如果不為-1，則表示此種type的View還沒有加載進(jìn)ViewGroup，利用ViewGroup.inflate(mContext, layoutResId, null);加載完相應(yīng)的View之后，如果mViewConstraintProvider（View的約束提供）不為空，則將View添加進(jìn)ViewGroup中并且添加相應(yīng)的依賴關(guān)系 ，所謂的依賴關(guān)系主要是mTargetViewId與view的依賴關(guān)系，mTargetViewId可以為界面title的id。

   /**
     * 如果有背景，則不需要隱藏其他view
     *
     * @param view
     * @return
     */
    private boolean hasBackground(View view) {
        if (mParent instanceof LinearLayout || mParent instanceof GridLayout) {
            return false;
        } else {
            Drawable drawable = view.getBackground();
            if (drawable instanceof ColorDrawable) {
                ColorDrawable colorDrawable = (ColorDrawable) drawable;
                int color = colorDrawable.getColor();
                return color != Color.TRANSPARENT;
            }
            return drawable instanceof BitmapDrawable;
        }
    }

如果mParent 是LinearLayout或者GridLayout，直接返回false。調(diào)用showLoading，showEmpty，showError等方法時(shí)，需要不顯示布局中其他View,因?yàn)檫@兩種ViewGroup布局原理的問題，需要直接隱藏其他View
如果不是上面的那兩種View，獲取他們的background，如果是ColorDrawable并且 colorDrawable.getColor()的值不是Color.TRANSPARENT；如果是BitmapDrawable則不隱藏，其他的一概隱藏

  /**
     * 按需隱藏相關(guān)的View
     *
     * @param type
     */
    private void hideViews(int type) {
        ViewGroup parent = mParent;
        int targetViewId = mTargetViewId;
        int count = mParent.getChildCount();
        List<Integer> referenceIds = null;
        //根據(jù)type獲取對(duì)應(yīng)的不受showEmpty、showLoading等控制的緩存id list
        if (mReferenceIds != null) {
            referenceIds = mReferenceIds.get(type);
        }
        int realIndex = mRealIndex.get(type, -1);
        type = isCollectionEmpty(referenceIds) ? -1 : type;
        List<View> views;
        //根據(jù)相應(yīng)的type做出相應(yīng)的隱藏邏輯
        switch (type) {
            case OTHER_TYPE:
                views = accordingToTypeShow(realIndex, referenceIds, mOnOtherReferenceIdsAction, parent, targetViewId);
                if (mOnOtherReferenceIdsAction != null) {
                    mOnOtherReferenceIdsAction.showOtherAction(views);
                }
                break;
            case LOADING_TYPE:
                views = accordingToTypeShow(realIndex, referenceIds, mOnLoadingReferenceIdsAction, parent, targetViewId);
                if (mOnLoadingReferenceIdsAction != null) {
                    mOnLoadingReferenceIdsAction.showLoadingAction(views);
                }
                break;
            case EMPTY_TYPE:
                views = accordingToTypeShow(realIndex, referenceIds, mOnEmptyReferenceIdsAction, parent, targetViewId);
                if (mOnEmptyReferenceIdsAction != null) {
                    mOnEmptyReferenceIdsAction.showEmptyAction(views);
                }
                break;
            case ERROR_TYPE:
                views = accordingToTypeShow(realIndex, referenceIds, mOnErrorReferenceIdsAction, parent, targetViewId);
                if (mOnErrorReferenceIdsAction != null) {
                    mOnErrorReferenceIdsAction.showErrorAction(views);
                }
                break;
            case NET_ERROR_TYPE:
                views = accordingToTypeShow(realIndex, referenceIds, mOnNetErrorReferenceIdsAction, parent, targetViewId);
                if (mOnNetErrorReferenceIdsAction != null) {
                    mOnNetErrorReferenceIdsAction.showNetErrorAction(views);
                }
                break;
            default:
                for (int i = 0; i < count; i++) {
                    //如果是當(dāng)前的type在parent中的真正索引等于當(dāng)前所以，跳過
                    if (i == realIndex) continue;
                    View view = parent.getChildAt(i);
                    //如果view的id==targetViewId 并且當(dāng)前View是Gone并且當(dāng)前view是ViewStub 跳過
                    if (targetViewId != view.getId()
                            && view.getVisibility() != GONE
                            && !(view instanceof ViewStub)
                    ) {
                        view.setVisibility(GONE);
                    }
                }
                break;
        }
    }

    
    private List<View> accordingToTypeHide(int realIndex, List<Integer> referenceIds, OnReferenceViewAction action, ViewGroup mParent, int mTargetViewId) {
        List<View> views = null;
        int childCount = mParent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            if (i == realIndex) continue;
            View view = mParent.getChildAt(i);
            int id = view.getId();
            //緩存中有此id，則此view不受showLoading、showEmpty等方法控制
            if (referenceIds.contains(id)) {
                //如果type對(duì)應(yīng)的OnReferenceViewAction不為空，將此id對(duì)應(yīng)的view添加至list中返回給上層，用于相應(yīng)方法調(diào)用時(shí)觸發(fā)
                if (action == null)continue;
                if (views==null){
                    views = new ArrayList<>();
                }
                    views.add(view);
                continue;
            }
            //如果view的id==targetViewId 并且當(dāng)前View是Gone并且當(dāng)前view是ViewStub 跳過
            if (mTargetViewId != view.getId()
                    && view.getVisibility() != GONE
                    && !(view instanceof ViewStub)) {
                view.setVisibility(GONE);
            }
        }
        return views;
    }

上面這段代碼的核心是處理布局中無條件隱藏的view，不必隱藏須滿足以下兩個(gè)條件：

• View的id是mTargetViewId
• View是ViewStub
  特殊說明：
  首先根據(jù)type獲取相應(yīng)緩存id list，type為L(zhǎng)OADING_TYPE時(shí)對(duì)應(yīng)loadingReferenceIds 和 OnLoadingReferenceIdsAction，OnLoadingReferenceIdsAction會(huì)回調(diào)loadingReferenceIds 中的views，以便對(duì)這些view單獨(dú)做處理。其他的type同理。

/**
     * 顯示
     */
    public void showContent() {
        if (mViewType == CONTENT_TYPE)
            return;
        mViewType = CONTENT_TYPE;
        int count = mParent.getChildCount();
        int size = mRealIndex.size();
        count -= size;
        List<Integer> contentIds = null;
        List<View> contentView = null;
        if (mReferenceIds != null) {
            contentIds = mReferenceIds.get(CONTENT_TYPE);
        }
        if (contentIds != null) {
            contentView = new ArrayList<>();
        }
        boolean hasContentAction = mOnContentReferenceIdsAction != null;
        for (int i = 0; i < count; i++) {
            View view = mParent.getChildAt(i);
            if (contentIds != null && contentIds.contains(view.getId())) {
                if (hasContentAction)
                    contentView.add(view);
                continue;
            }
            if (!(view instanceof ViewStub) && view.getVisibility() != VISIBLE) {
                view.setVisibility(VISIBLE);
            }
        }
        for (int i = 0; i < size; i++) {
            mParent.getChildAt(mRealIndex.valueAt(i)).setVisibility(GONE);
        }
        if (hasContentAction) {
            mOnContentReferenceIdsAction.showContentAction(contentView);
        }
    }

showContent()這個(gè)方法用于顯示布局中原有的控件。網(wǎng)絡(luò)請(qǐng)求成功之后您就可以調(diào)用這個(gè)方法。
首先獲取mReferenceIds緩存的CONTENT_TYPE的ids，遍歷parent中的view如果view的id在contentIds中，并且OnContentReferenceIdsAction不為空，將view添加至contentView中。
最后OnContentReferenceIdsAction不為空，將contentview返回供上層調(diào)用處理。

接下來我們看看自動(dòng)生成相關(guān)Layout的代碼類——MultiStatusProcessor

具體關(guān)于APT相關(guān)介紹不是本文重點(diǎn)，如果感興趣自己可以google/baidu。

@Override
    public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {
        Set<? extends Element> elements = roundEnvironment.getElementsAnnotatedWith(MultiStatus.class);
        if (elements == null || elements.isEmpty()) {
            return true;
        }
        mMessager.printMessage(Diagnostic.Kind.NOTE, "<<<<<<<<<<<<<<<<<<< MultiStatusProcessor process START >>>>>>>>>>>>>>>");
        Map<String, String> viewProviderMap = new HashMap<>();
        List<String> viewClassList = new ArrayList<>();
        List<String> providerClassList = new ArrayList<>();
        //解析MultiStatus注解里面value和provider
        parseParam(elements, viewClassList, providerClassList);
        //將解析出來的value和provider合并
        mergeList(viewClassList, providerClassList, viewProviderMap);
        try {
            //真正生成代碼的地方
            generate(viewProviderMap);
        } catch (IOException  e) {
            mMessager.printMessage(Diagnostic.Kind.ERROR, "Exception occurred when generating class file.");
            e.printStackTrace();
        }
        mMessager.printMessage(Diagnostic.Kind.NOTE, "<<<<<<<<<<<<<<<<<<< MultiStatusProcessor process END >>>>>>>>>>>>>>>");
        return true;
    }

APT自動(dòng)化生成代碼的核心方法。

• 解析注解MultiStatus中的value和provider中的值
• 需要value和provider中的值對(duì)應(yīng)順序一致，然后進(jìn)行合并操作
• 核心的代碼生成邏輯

   private void generate(Map<String, String> viewProviderMap) throws IOException {
        for (Map.Entry<String, String> entry : viewProviderMap.entrySet()) {
            String clazz = entry.getKey();
            String provider = entry.getValue();
            int lastDotIndex = clazz.lastIndexOf(".");
            String superPackageName = clazz.substring(0, lastDotIndex);
            String superClassName = clazz.substring(lastDotIndex + 1);
            String className;
            //因?yàn)榈谝粋€(gè)版本只支持RelativeLayout，當(dāng)時(shí)類名為MultiStatusLayout
            //為了兼容后期其他Layout，生成類的前面都加MultiStatus，例如：MultiStatusLinearLayout
            if (superClassName.equals("RelativeLayout")) {
                className = CLASS_PREFIX + "Layout";
            } else {
                className = CLASS_PREFIX + superClassName;
            }

            mMessager.printMessage(Diagnostic.Kind.NOTE, clazz + "=======>" + className);

            TypeSpec.Builder builder = TypeSpec.classBuilder(className)
                    .addJavadoc(CLASS_JAVA_DOC)
                    // 注釋 1
                    .addModifiers(Modifier.PUBLIC)
                    // 注釋 2
                    .superclass(ClassName.get(superPackageName, superClassName))
                    // 注釋 3
                    .addSuperinterface(ClassName.get(PACKAGE_NAME, "MultiStatusEvent"))
                    //注釋 4
                    .addField(ClassName.get(PACKAGE_NAME, "MultiStatusHelper"), "mMultiStatusHelper", Modifier.PRIVATE);
            //生成方法的具體操作
            generateMethod(builder, clazz, provider);

            JavaFile javaFile = JavaFile.builder(PACKAGE_NAME, builder.build()).build();
            javaFile.writeTo(mFilter);
        }
    }

1.生成類是public
2.定義生成類的全路徑包名，類名
3.生成的類實(shí)現(xiàn)MultiStatusEvent接口
4.生成類添加成員變量mMultiStatusHelper

  private void constructor(TypeSpec.Builder builder, String clazz, String providerClassPath) {
        TypeName contextType = ClassName.get("android.content", "Context");
        TypeName attributeSetType = ClassName.get("android.util", "AttributeSet");
        MethodSpec constructorOne = MethodSpec.constructorBuilder()
                .addModifiers(Modifier.PUBLIC)
                .addParameter(contextType, "context")
                .addStatement("this(context,null)")
                .build();
        MethodSpec constructorTwo = MethodSpec.constructorBuilder()
                .addModifiers(Modifier.PUBLIC)
                .addParameter(contextType, "context")
                .addParameter(attributeSetType, "attrs")
                .addStatement("this(context,attrs,0)")
                .build();
        MethodSpec constructorThree = MethodSpec.constructorBuilder()
                .addModifiers(Modifier.PUBLIC)
                .addParameter(contextType, "context")
                .addParameter(attributeSetType, "attrs")
                .addParameter(TypeName.INT, "defStyleAttr")
                .addStatement("super(context,attrs,defStyleAttr)")
                .addStatement("mMultiStatusHelper = new MultiStatusHelper(context,attrs,defStyleAttr,this)")
                //注釋1
                .addStatement("generateProviderClass($S)", providerClassPath)
                .build();
        builder.addMethod(constructorOne)
                .addMethod(constructorTwo)
                .addMethod(constructorThree);
    }

上面代碼片段是生成類構(gòu)造器，因?yàn)樯傻念愐彩荓ayout，所以需要構(gòu)造View的基本構(gòu)造器，最終還是交由MultiStatusHelper中處理。
注釋1：providerClassPath為，實(shí)現(xiàn)ViewConstraintProvider接口的全路徑，利用generateProviderClass（）方法生成相應(yīng)的class，然后供后續(xù)使用。

 private void setViewConstraintProviderClass(TypeSpec.Builder builder, String className, String providerClassPath) {
        MethodSpec methodSpec = MethodSpec.methodBuilder("generateProviderClass")
                .addModifiers(Modifier.PRIVATE)
                .addParameter(String.class, "providerClassPath")
                .beginControlFlow("if(providerClassPath == null)")
                .addStatement("return")
                .endControlFlow()
                .beginControlFlow("try")
                .addStatement("$T providerClass = $T.forName(providerClassPath)", Class.class, Class.class)
                .addStatement("mMultiStatusHelper.setViewConstraintProvider(providerClass)")
                .addStatement("} catch ($T e) { \n e.printStackTrace()", ClassNotFoundException.class)
                .endControlFlow()
                .build();
        builder.addMethod(methodSpec);
    }

上面代碼片段是生成generateProviderClass（String providerClassPath）的代碼。
最終編譯生成的java代碼如下：

private void generateProviderClass(String providerClassPath) {
    if(providerClassPath == null) {
      return;
    }
    try {
      Class providerClass = Class.forName(providerClassPath);
      mMultiStatusHelper.setViewConstraintProvider(providerClass);
      } catch (ClassNotFoundException e) { 
           e.printStackTrace();
    }
  }

終于嗶嗶嗶嗶完了，太難了?。?！您只看到我扣在屏幕上的字，卻看不到我滴在鍵盤上的淚(′??Д??`)。
如果有什么問題。請(qǐng)發(fā)送郵件至pittleeeeee@gmail.com