DataBinding整體使用流程
整體流程圖.png
開發(fā)階段
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"@{}"標識符
<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="測試"/>
</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();
}
});
}
}
編譯階段
1.Databinding會自動解析識別xml中的"@{}"標識符谷婆，并在以下目錄生成2個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
帶“@{}”的xml文件是android系統(tǒng)無法識別的慨蛙，為了向后兼容辽聊，需要在編譯期統(tǒng)一轉(zhuǎn)換成系統(tǒng)能識別的標準xml布局，而原先在布局中添加的"@{}"期贫，"@{三目運算符}"等信息跟匆，則會存儲在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="測試"/>
</LinearLayout>
activity_main-layout.xml（xml描述文件）
1.任何view只要用到了"@{}"標識通砍，就會在activity_main-layout.xml中生成target描述玛臂，并根據(jù)該view在parent中的位置生成"binding_[index]"標識，并設(shè)置在tag中封孙。
2.如果一個view即沒有設(shè)置"android:id"迹冤，也沒有使用"@{}"標識，則不會在activity_main-layout.xml中生成這個view的target描述虎忌。
3.LinearLayout比較特殊泡徙，并沒有設(shè)置"android:id"，也沒有使用"@{}"膜蠢，但還是會生成一個默認的tag="layout/activity_main_0"堪藐，表示它是根布局，在ViewDataBinding.java實例化時狡蝶，需要判斷根布局的tag庶橱，后面源碼會分析到。
<?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根據(jù)解析后的activity_main-layout.xml贪惹，和layout下的activity_main.xml文件苏章，生成build/intermediates/classes/debug/[項目路徑]/databinding/
ActivityMainBinding.java和BR.java
ActivityMainBinding目錄.png
ActivityMainBinding主要具備以下功能
1.作為view和model的連接器，持有需要展示的數(shù)據(jù)和views的成員變量
2.將數(shù)據(jù)映射到view（就是setText奏瞬，setOnClick等）
3.在UI線程更新數(shù)據(jù)
BR.java就是一個常量類
可以通過binding.setVariable(BRuser, new User())進行數(shù)據(jù)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;
}
運行階段
Databinding框架最主要做的事枫绅，就是以上2步，接下來就是在代碼中調(diào)用生成的ViewDataBinding硼端，并進行數(shù)據(jù)綁定操作并淋。
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);// 最終調(diào)用的還是activity.setContentView()，不過這里的layoutId是已經(jīng)去掉"@{}"的標準xml布局
View decorView = activity.getWindow().getDecorView();
ViewGroup contentView = (ViewGroup) decorView.findViewById(android.R.id.content);//獲取根頂級容器view
return bindToAddedViews(bindingComponent, contentView, 0, layoutId);
}
取出布局的rootView珍昨，調(diào)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) {
// 從頂級容器view中獲取當前布局的rootView县耽，調(diào)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:
// 將rootView傳遞給ActivityMainBinding.bind()
return com.listen.test_databinding.databinding.ActivityMainBinding.bind(view, bindingComponent);
}
return null;
}
此處做了rootView的判斷，如果傳遞過來的不是當前ViewDataBinding綁定的布局镣典，則拋異常兔毙。所以即使rootView沒有設(shè)置id，及"@{}"兄春，在info-layout.xml中也會生成相應(yīng)的target描述澎剥。
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在此處初始化
}
}
這里需要特別注意的是在編譯期自動生成的activity_main.xml文件中自動添加了tag="binding_1"，"binding_2"等赶舆，其實在初始化完這些view后哑姚，都已經(jīng)清空祭饭，是不影響我們在代碼中設(shè)置tag的；不過rootView并沒有清除tag（就是xml布局最外層的layout）叙量，如果>=14以上版本倡蝙，在代碼里設(shè)置setTag(R.id.databinding,"anything")，或宛乃，<14版本悠咱，在代碼里設(shè)置setTag("anything")，則會報錯征炼，so析既，這個tag是由DataBinding占著的，使用上得小心谆奥。
public ActivityMainBinding(android.databinding.DataBindingComponent bindingComponent, View root) {
super(bindingComponent, root, 0);
// 遍歷布局眼坏，找到所有views，并存儲在bindings[]中酸些，5表示布局一共有5個view宰译，sIncludes存儲被include進 // 來的布局，sViewsWithIds存儲設(shè)置了"android:id"魄懂，但是沒有用到"@{}"的view
Object[] bindings = mapBindings(bindingComponent, root, 5, sIncludes, sViewsWithIds);
// 將bindings[]中的view取出沿侈，賦值給當前各個view的成員變量，并清除tag市栗，避免沖突
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);
}
}
*/
// 請求刷新缀拭，實現(xiàn)數(shù)據(jù)與view的綁定
this.invalidateAll();
}
mapBindings()，其實就是遞歸遍歷view樹的過程填帽，不過不是byId蛛淋，而是byTag，尋找以"binding_"開頭的view篡腌，并取出"binding_[索引]"中的索引褐荷，賦值給binding[]數(shù)組。所有的view只在一次遍歷中獲得嘹悼，而如果是用findViewById的方式叛甫，每次調(diào)用都需要遍歷一次view樹[性能對比]。需要特別注意的是binding數(shù)組的元素不一定都是view或viewGroup杨伙，如果有include布局的時候binding數(shù)組存儲的可能是include布局的viewDataBinding對象合溺。
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，則從"layout/activity_main_0"中取出索引"0"缀台，設(shè)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_")) {
// 同樣判斷tag，取出"binding_1"哮奇，"bingding_2"中的索引膛腐，賦值到bindings[]中
viewGroup = parseTagInt(tag, BINDING_NUMBER_START);
if(bindings[viewGroup] == null) {
bindings[viewGroup] = view;
}
...
}
// isBound=false睛约，說明當前的view既不是根布局，也沒有用到"@{}"（如果有用到就會生成"binding_"
// 的tag）哲身；則通過id獲取該view辩涝，并設(shè)置到bingding[]
// 如果存在設(shè)置了id，但是沒有“@{}”的view會被添加到sViewsWithIds中勘天，如果
// "binding_[index]"的index最大為3怔揩，則view的起始index設(shè)置為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是個viewGroup脯丝，則遍歷子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) {
// 如果當前view也是一個rootView商膊，則判斷tag中是否有include標識信息
// 如果包含include標簽，生成的info-layout文件應(yīng)該是以下樣式：
// <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信息宠进，則重新調(diào)用DataBindingUtil.bind()生成ViewDataBinding晕拆，重復(fù)當前流程，
// 不過當前的bindings[index]就不是一個view材蹬，而是一個viewDataBinding
bindings[index] = DataBindingUtil.bind(bindingComponent, child, layoutId);
...
}
}
}
if(!isInclude) {
// 如果只是一個viewGroup实幕，不是include進來的布局，則重新調(diào)用mapBindings堤器，只是isRoot=false昆庇，則會上面進入"binding_"的判斷邏輯
mapBindings(bindingComponent, child, bindings, includes, viewsWithIds, false);
}
}
}
}
}
view遍歷流程圖
view遍歷流程.png
View都找到了，現(xiàn)在該是時候設(shè)置listener闸溃，data的時候了整吆。這時候會通過invalidateAll()請求數(shù)據(jù)更新，層層調(diào)用后圈暗，還是回到了ActivityMainBinding的executeBindings()掂为，在這個方法里將更新后的model數(shù)據(jù)，onclick等重新設(shè)置到Textview员串，Button上勇哗，完成了model->view的單向綁定。
// 子類：xxxViewDataBinding extends ViewDataBinding
public void invalidateAll() {
synchronized(this) {
this.mDirtyFlags = 4L;
}
this.requestRebind();
}
// 父類：ViewDataBinding.java
// 通過handler.post()執(zhí)行mRebindRunnable
protected void requestRebind() {
...
mUIThreadHandler.post(mRebindRunnable);
}
// mRebindRunnable調(diào)用了executePendingBindings()
private final Runnable mRebindRunnable = new Runnable() {
@Override
public void run() {
...
executePendingBindings();
}
};
// executePendingBindings調(diào)用了executeBindings()
public void executePendingBindings() {
...
executeBindings();
...
}
// 子類：xxxViewDataBinding extends ViewDataBinding
protected void executeBindings() {
...
// 當調(diào)用ViewDataBinding.setUser(new User())時寸齐，就是給成員變量mUser賦值欲诺，在這里獲取this.mUser
UserModel user = this.mUser;
if((dirtyFlags & 6L) != 0L) {
// 獲取并構(gòu)建數(shù)據(jù)，所以model中的字段要么為public渺鹦，要么提供一個getter方法扰法，不然這里無法獲取
// 可以看到，在xml中的@{}表達式毅厚，此時已經(jīng)解析成對應(yīng)的方法isAge18塞颁，user.name等
if(user != null) {
userIsAge18User = user.isAge18();
nameUser = user.name;
nickNameUser = user.nickName;
}
...
// 獲取并構(gòu)建數(shù)據(jù)
userIsAge18UserStrin = userIsAge18User?"man":"boy";
stringNameUser = "名字" + nameUser;
ObjectnullNickNameUs1 = null == nickNameUser;
...
objectnullNickNameUs = ObjectnullNickNameUs1?0:8;
}
// 設(shè)置listener
if((dirtyFlags & 5L) != 0L) {
this.btnTest.setOnClickListener(testClick);
}
// 通過TextViewBindingAdapter將數(shù)據(jù)設(shè)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);
}
}
以上便是當我們通過DataBindingUtil.setContentView()對Databinding進行初始化，以及當我們獲取到最新數(shù)據(jù)，通過Binding.setModel進行數(shù)據(jù)更新時的操作流程祠锣。
數(shù)據(jù)綁定流程.png
參考
英文官方文檔
https://developer.android.com/topic/libraries/data-binding/index.html
Google開發(fā)團隊介紹DataDinding使用
https://realm.io/cn/news/data-binding-android-boyar-mount/?utm_source=tuicool&utm_medium=referral
QQ音樂團隊分享酷窥，比較貼近源碼的介紹
http://gold.xitu.io/entry/57e48e7ba22b9d006139c60b
