DataBinding学习笔记(一)源码分析
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DataBinding整体使用流程
开发阶段
UserModel.java
public class UserModel { public String name; public String nickName; public int age; public UserModel(String name, String nickName, int age) { this.name = name; this.age = age; this.nickName = nickName; } public boolean isAge18() { return age >= 18; }}
activity_main.xml
在xml中使用”@{}”标识符
<layout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools"> <data> <variable name="user" type="com.listen.test_databinding.UserModel"/> <variable name="testClick" type="android.view.View.OnClickListener"/> <import type="android.view.View"/> </data> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context="com.listen.test_databinding.MainActivity"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text='@{"名字" + user.name}'/> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text='@{user.nickName}' android:visibility="@{null == user.nickName ? View.VISIBLE : View.GONE}"/> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text='@{user.isAge18() ? "man" : "boy"}'/> <Button android:id="@+id/btn_test" android:layout_width="match_parent" android:layout_height="50dp" android:onClick="@{testClick}" android:text="测试"/> </LinearLayout></layout>
MainActivity.java
public class MainActivity extends AppCompatActivity { private ActivityMainBinding mBinding; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mBinding = DataBindingUtil.setContentView(this, R.layout.activity_main); final UserModel user = new UserModel("listen", "ls", 18); mBinding.setUser(user); mBinding.setTestClick(new View.OnClickListener() { @Override public void onClick(View view) { Toast.makeText(MainActivity.this, "testClick", Toast.LENGTH_SHORT).show(); } }); }}
编译阶段
1.Databinding会自动解析识别xml中的”@{}”标识符,并在以下目录生成2个xml文件
1.build/intermediates/data-binding-layout-out/activity_main.xml
2.build/intermediates/data-binding-info/debug/activity_main-layout.xml
activity_main.xml
带“@{}”的xml文件是android系统无法识别的,为了向后兼容,需要在编译期统一转换成系统能识别的标准xml布局,而原先在布局中添加的”@{}”,”@{三目运算符}”等信息,则会存储在activity_main-layout.xml中。
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:tag="layout/activity_main_0" tools:context="com.listen.test_databinding.MainActivity"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:tag="binding_1"/> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:tag="binding_2" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:tag="binding_3"/> <Button android:id="@+id/btn_test" android:layout_width="match_parent" android:layout_height="50dp" android:tag="binding_4" android:text="测试"/></LinearLayout>
activity_main-layout.xml(xml描述文件)
1.任何view只要用到了”@{}”标识,就会在activity_main-layout.xml中生成target描述,并根据该view在parent中的位置生成”binding_[index]”标识,并设置在tag中。
2.如果一个view即没有设置”android:id”,也没有使用”@{}”标识,则不会在activity_main-layout.xml中生成这个view的target描述。
3.LinearLayout比较特殊,并没有设置”android:id”,也没有使用”@{}”,但还是会生成一个默认的tag=”layout/activity_main_0”,表示它是根布局,在ViewDataBinding.java实例化时,需要判断根布局的tag,后面源码会分析到。
<?xml version="1.0" encoding="utf-8" standalone="yes"?><Layout absoluteFilePath="/Users/lisong/Documents/AndroidStudioWorkSpace/Test_Databinding/app/src/main/res/layout/activity_main.xml" directory="layout" isMerge="false" layout="activity_main" modulePackage="com.listen.test_databinding"> <Variables name="user" declared="true" type="com.listen.test_databinding.UserModel"> ... </Variables> <Variables name="testClick" declared="true" type="android.view.View.OnClickListener"> ... </Variables> <Imports name="View" type="android.view.View"> ... </Imports> <Targets> <Target tag="layout/activity_main_0" view="LinearLayout"> <Expressions/> ... </Target> <Target tag="binding_1" view="TextView"> <Expressions> <Expression attribute="android:text" text=""名字" + user.name"> ... </Expression> </Expressions> </Target> <Target tag="binding_2" view="TextView"> <Expressions> <Expression attribute="android:text" text="user.nickName"> ... </Expression> <Expression attribute="android:visibility" text="null == user.nickName ? View.VISIBLE : View.GONE"> ... </Expression> </Expressions> </Target> <Target tag="binding_3" view="TextView"> <Expressions> <Expression attribute="android:text" text="user.isAge18() ? "man" : "boy""> ... </Expression> </Expressions> </Target> <Target id="@+id/btn_test" tag="binding_4" view="Button"> <Expressions> <Expression attribute="android:onClick" text="testClick"> ... </Expression> </Expressions> </Target> </Targets></Layout>
2.生成ActivityMainBinding.java和BR.java
DataBinding根据解析后的activity_main-layout.xml,和layout下的activity_main.xml文件,生成build/intermediates/classes/debug/[项目路径]/databinding/
ActivityMainBinding.java和BR.java
ActivityMainBinding主要具备以下功能
1.作为view和model的连接器,持有需要展示的数据和views的成员变量
2.将数据映射到view(就是setText,setOnClick等)
3.在UI线程更新数据
BR.java就是一个常量类
可以通过binding.setVariable(BRuser, new User())进行数据更新
public class BR { public static final int _all = 0; public static final int testClick = 1; public static final int user = 2; public BR() { }}
public boolean setVariable(int variableId, Object variable) { switch(variableId) { case BR.testClick : setTestClick((android.view.View.OnClickListener) variable); return true; case BR.user : setUser((com.listen.test_databinding.UserModel) variable); return true; } return false;}
运行阶段
Databinding框架最主要做的事,就是以上2步,接下来就是在代码中调用生成的ViewDataBinding,并进行数据绑定操作。
DataBindingUtil是一切的入口
ActivityMainBinding mBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);
public static <T extends ViewDataBinding> T setContentView(Activity activity, int layoutId, DataBindingComponent bindingComponent) { activity.setContentView(layoutId);// 最终调用的还是activity.setContentView(),不过这里的layoutId是已经去掉"@{}"的标准xml布局 View decorView = activity.getWindow().getDecorView(); ViewGroup contentView = (ViewGroup) decorView.findViewById(android.R.id.content);//获取根顶级容器view return bindToAddedViews(bindingComponent, contentView, 0, layoutId);}
取出布局的rootView,调用ActivityMainBinding.bind()
private static <T extends ViewDataBinding> T bindToAddedViews(android.databinding.DataBindingComponent component, ViewGroup parent, int startChildren, int layoutId) { final int endChildren = parent.getChildCount(); final int childrenAdded = endChildren - startChildren; if (childrenAdded == 1) { // 从顶级容器view中获取当前布局的rootView,调用bind方法 final View childView = parent.getChildAt(endChildren - 1); return bind(component, childView, layoutId); } else { ... }}static <T extends ViewDataBinding> T bind(DataBindingComponent bindingComponent, View root, int layoutId) { // sMapper = DataBinderMapper.java return (T) sMapper.getDataBinder(bindingComponent, root, layoutId);}/** DataBinderMapper.java */public android.databinding.ViewDataBinding getDataBinder(android.databinding.DataBindingComponent bindingComponent, android.view.View view, int layoutId) { switch(layoutId) { case com.listen.test_databinding.R.layout.activity_main: // 将rootView传递给ActivityMainBinding.bind() return com.listen.test_databinding.databinding.ActivityMainBinding.bind(view, bindingComponent); } return null;}
此处做了rootView的判断,如果传递过来的不是当前ViewDataBinding绑定的布局,则抛异常。所以即使rootView没有设置id,及”@{}”,在info-layout.xml中也会生成相应的target描述。
public static ActivityMainBinding bind(View view, DataBindingComponent bindingComponent) { if(!"layout/activity_main_0".equals(view.getTag())) { throw new RuntimeException("view tag isn\'t correct on view:" + view.getTag()); } else { return new ActivityMainBinding(bindingComponent, view); // ActivityMainBinding在此处初始化 }}
这里需要特别注意的是在编译期自动生成的activity_main.xml文件中自动添加了tag=”binding_1”,”binding_2”等,其实在初始化完这些view后,都已经清空,是不影响我们在代码中设置tag的;不过rootView并没有清除tag(就是xml布局最外层的layout),如果>=14以上版本,在代码里设置setTag(R.id.databinding,”anything”),或,<14版本,在代码里设置setTag(“anything”),则会报错,so,这个tag是由DataBinding占着的,使用上得小心。
public ActivityMainBinding(android.databinding.DataBindingComponent bindingComponent, View root) { super(bindingComponent, root, 0); // 遍历布局,找到所有views,并存储在bindings[]中,5表示布局一共有5个view,sIncludes存储被include进 // 来的布局,sViewsWithIds存储设置了"android:id",但是没有用到"@{}"的view Object[] bindings = mapBindings(bindingComponent, root, 5, sIncludes, sViewsWithIds); // 将bindings[]中的view取出,赋值给当前各个view的成员变量,并清除tag,避免冲突 this.btnTest = (Button)bindings[4]; this.btnTest.setTag((Object)null); this.mboundView0 = (LinearLayout)bindings[0]; this.mboundView0.setTag((Object)null); this.mboundView1 = (TextView)bindings[1]; this.mboundView1.setTag((Object)null); this.mboundView2 = (TextView)bindings[2]; this.mboundView2.setTag((Object)null); this.mboundView3 = (TextView)bindings[3]; this.mboundView3.setTag((Object)null); this.setRootTag(root); /** ViewDatabBinding.java protected void setRootTag(View view) { //private static final boolean USE_TAG_ID = DataBinderMapper.TARGET_MIN_SDK >= 14; if (USE_TAG_ID) { view.setTag(R.id.dataBinding, this); } else { view.setTag(this); } } */ // 请求刷新,实现数据与view的绑定 this.invalidateAll();}
mapBindings(),其实就是递归遍历view树的过程,不过不是byId,而是byTag,寻找以”binding_”开头的view,并取出”binding_[索引]”中的索引,赋值给binding[]数组。所有的view只在一次遍历中获得,而如果是用findViewById的方式,每次调用都需要遍历一次view树[性能对比]。需要特别注意的是binding数组的元素不一定都是view或viewGroup,如果有include布局的时候binding数组存储的可能是include布局的viewDataBinding对象。
private static void mapBindings(DataBindingComponent bindingComponent, View view, Object[] bindings, ViewDataBinding.IncludedLayouts includes, SparseIntArray viewsWithIds, boolean isRoot) { ViewDataBinding existingBinding = getBinding(view); if(existingBinding == null) { Object objTag = view.getTag(); String tag = objTag instanceof String?(String)objTag:null; if(isRoot && tag != null && tag.startsWith("layout")) { // 如果是rootView,则从"layout/activity_main_0"中取出索引"0",设置到bindings[0]中 viewGroup = tag.lastIndexOf(95); count = parseTagInt(tag, viewGroup + 1); if(bindings[count] == null) { bindings[count] = view; } ... } else if(tag != null && tag.startsWith("binding_")) { // 同样判断tag,取出"binding_1","bingding_2"中的索引,赋值到bindings[]中 viewGroup = parseTagInt(tag, BINDING_NUMBER_START); if(bindings[viewGroup] == null) { bindings[viewGroup] = view; } ... } // isBound=false,说明当前的view既不是根布局,也没有用到"@{}"(如果有用到就会生成"binding_" // 的tag);则通过id获取该view,并设置到bingding[] // 如果存在设置了id,但是没有“@{}”的view会被添加到sViewsWithIds中,如果 // "binding_[index]"的index最大为3,则view的起始index设置为4。 // static { // sIncludes = null; // sViewsWithIds = new android.util.SparseIntArray(); // sViewsWithIds.put(R.id.btn_test, 4); //} if(!isBound) { viewGroup = view.getId(); if(viewGroup > 0 && viewsWithIds != null && (count = viewsWithIds.get(viewGroup, -1)) >= 0 && bindings[count] == null) { bindings[count] = view; } } if(view instanceof ViewGroup) { // 如果是view是个viewGroup,则遍历子view ViewGroup var25 = (ViewGroup)view; count = var25.getChildCount(); ... for(int i = 0; i < count; ++i) { View child = var25.getChildAt(i); boolean isInclude = false; if(indexInIncludes >= 0 && child.getTag() instanceof String) { String childTag = (String)child.getTag(); if(childTag.endsWith("_0") && childTag.startsWith("layout") && childTag.indexOf(47) > 0) { // 如果当前view也是一个rootView,则判断tag中是否有include标识信息 // 如果包含include标签,生成的info-layout文件应该是以下样式: // <Target include="include_main" tag="layout/activity_main_0"> // </Target> int includeIndex = findIncludeIndex(childTag, minInclude, includes, indexInIncludes); if(includeIndex >= 0) { isInclude = true; ... // 如果包含include信息,则重新调用DataBindingUtil.bind()生成ViewDataBinding,重复当前流程, // 不过当前的bindings[index]就不是一个view,而是一个viewDataBinding bindings[index] = DataBindingUtil.bind(bindingComponent, child, layoutId); ... } } } if(!isInclude) { // 如果只是一个viewGroup,不是include进来的布局,则重新调用mapBindings,只是isRoot=false,则会上面进入"binding_"的判断逻辑 mapBindings(bindingComponent, child, bindings, includes, viewsWithIds, false); } } } }}
view遍历流程图
View都找到了,现在该是时候设置listener,data的时候了。这时候会通过invalidateAll()请求数据更新,层层调用后,还是回到了ActivityMainBinding的executeBindings(),在这个方法里将更新后的model数据,onclick等重新设置到Textview,Button上,完成了model->view的单向绑定。
// 子类:xxxViewDataBinding extends ViewDataBindingpublic void invalidateAll() { synchronized(this) { this.mDirtyFlags = 4L; } this.requestRebind();}// 父类:ViewDataBinding.java// 通过handler.post()执行mRebindRunnableprotected void requestRebind() { ... mUIThreadHandler.post(mRebindRunnable);}// mRebindRunnable调用了executePendingBindings()private final Runnable mRebindRunnable = new Runnable() { @Override public void run() { ... executePendingBindings(); }};// executePendingBindings调用了executeBindings()public void executePendingBindings() { ... executeBindings(); ...}// 子类:xxxViewDataBinding extends ViewDataBindingprotected void executeBindings() { ... // 当调用ViewDataBinding.setUser(new User())时,就是给成员变量mUser赋值,在这里获取this.mUser UserModel user = this.mUser; if((dirtyFlags & 6L) != 0L) { // 获取并构建数据,所以model中的字段要么为public,要么提供一个getter方法,不然这里无法获取 // 可以看到,在xml中的@{}表达式,此时已经解析成对应的方法isAge18,user.name等 if(user != null) { userIsAge18User = user.isAge18(); nameUser = user.name; nickNameUser = user.nickName; } ... // 获取并构建数据 userIsAge18UserStrin = userIsAge18User?"man":"boy"; stringNameUser = "名字" + nameUser; ObjectnullNickNameUs1 = null == nickNameUser; ... objectnullNickNameUs = ObjectnullNickNameUs1?0:8; } // 设置listener if((dirtyFlags & 5L) != 0L) { this.btnTest.setOnClickListener(testClick); } // 通过TextViewBindingAdapter将数据设置到TextView上 if((dirtyFlags & 6L) != 0L) { TextViewBindingAdapter.setText(this.mboundView1, stringNameUser); TextViewBindingAdapter.setText(this.mboundView2, nickNameUser); this.mboundView2.setVisibility(objectnullNickNameUs); TextViewBindingAdapter.setText(this.mboundView3, userIsAge18UserStrin); }}
以上便是当我们通过DataBindingUtil.setContentView()对Databinding进行初始化,以及当我们获取到最新数据,通过Binding.setModel进行数据更新时的操作流程。
参考
英文官方文档
https://developer.android.com/topic/libraries/data-binding/index.html
Google开发团队介绍DataDinding使用
https://realm.io/cn/news/data-binding-android-boyar-mount/?utm_source=tuicool&utm_medium=referral
QQ音乐团队分享,比较贴近源码的介绍
http://gold.xitu.io/entry/57e48e7ba22b9d006139c60b
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