1.使用
在app级的build.gradle文件中添加
dataBinding {
enabled = true
}我使用的是kotlin，还添加kapt了
plugins { id 'kotlin-kapt' }然后布局文件添加layout
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
<data>
<variable
name="user"
type="com.example.kotlinweather.ui.databin.User" />
<variable
name="m1"
type="java.lang.String" />
<variable
name="listener"
type="android.view.View.OnClickListener" />
</data>
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/userName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@{user.name}"
android:textSize="20sp"/>
<TextView
android:id="@+id/userPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@={user.password}"
android:textSize="20sp"
android:onClickListener="@{listener}"/>
</LinearLayout>
</layout>javaBean类：
class User(userName: String, userPassword: String): BaseObservable() {
var name = userName
@Bindable
get() = field
set(value) {
field = value
notifyPropertyChanged(BR.name)
}
var password = userPassword
@Bindable
get() = field
set(value) {
field = value
notifyPropertyChanged(BR.password)
}
}activity使用：
class DataBindTestActivity: AppCompatActivity() {
lateinit var binding: ActivityDataBindTestBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = DataBindingUtil.setContentView(this, R.layout.activity_data_bind_test)
binding.lifecycleOwner = this
val user = User("xh", "123456")
binding.user = user
user.password = "123456789"
}
}显示结果：
2.生成的文件
1.对应的Binding.java文件
路径：app/build/generated/data_binding_base_class_source_out/debug/out/项目/databinding下生成了对应的Binding.java文件
public abstract class ActivityDataBindTestBinding extends ViewDataBinding {
@NonNull
public final TextView userName;
@NonNull
public final TextView userPassword;
@Bindable
protected User mUser;
@Bindable
protected String mM1;
@Bindable
protected View.OnClickListener mListener;
protected ActivityDataBindTestBinding(Object _bindingComponent, View _root, int _localFieldCount,
TextView userName, TextView userPassword) {
super(_bindingComponent, _root, _localFieldCount);
this.userName = userName;
this.userPassword = userPassword;
}
public abstract void setUser(@Nullable User user);
@Nullable
public User getUser() {
return mUser;
}
.......
}咱们在layout中设置的对应的变量在这个文件中都有对应的set/get方法且对应的View也有。
2.BR.java
路径app/build/generated/source/kapt/debug中，这个文件在这个路径下的2个文件夹中都存在
3.DataBinderMapperImpl.java
路径app/build/generated/source/kapt/debug中，这个文件在这个路径下的2个文件夹中都存在，但是继承和实现不一样。
4.ActivityDataBindTestBindingImpl.java文件
路径app/build/generated/source/kapt/debug/项目包/databinding中
5.对应的-layout布局
有2个文件，第一个路径：app/build/intermediates/data_binding_layout_info_type_merge/debug/out下
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<Layout directory="layout" filePath="app\src\main\res\layout\activity_data_bind_test.xml"
isBindingData="true" isMerge="false"
layout="activity_data_bind_test" modulePackage="com.example.kotlinweather" rootNodeType="android.widget.LinearLayout">
<Variables name="user" declared="true" type="com.example.kotlinweather.ui.databin.User">
<location endLine="6" endOffset="62" startLine="4" startOffset="8" />
</Variables>
<Variables name="m1" declared="true" type="java.lang.String">
<location endLine="9" endOffset="37" startLine="7" startOffset="8" />
</Variables>
<Variables name="listener" declared="true" type="android.view.View.OnClickListener">
<location endLine="12" endOffset="54" startLine="10" startOffset="8" />
</Variables>
<Targets>
<Target tag="layout/activity_data_bind_test_0" view="LinearLayout">
<Expressions />
<location endLine="35" endOffset="18" startLine="15" startOffset="4" />
</Target>
<Target id="@+id/userName" tag="binding_1" view="TextView">
<Expressions>
<Expression attribute="android:text" text="user.name">
<Location endLine="24" endOffset="38" startLine="24" startOffset="12" />
<TwoWay>false</TwoWay>
<ValueLocation endLine="24" endOffset="36" startLine="24" startOffset="28" />
</Expression>
</Expressions>
<location endLine="25" endOffset="36" startLine="20" startOffset="8" />
</Target>
<Target id="@+id/userPassword" tag="binding_2" view="TextView">
<Expressions>
<Expression attribute="android:text" text="user.password">
<Location endLine="31" endOffset="43" startLine="31" startOffset="12" />
<TwoWay>true</TwoWay>
<ValueLocation endLine="31" endOffset="41" startLine="31" startOffset="29" />
</Expression>
<Expression attribute="android:onClickListener" text="listener">
<Location endLine="33" endOffset="48" startLine="33" startOffset="12" />
<TwoWay>false</TwoWay>
<ValueLocation endLine="33" endOffset="46" startLine="33" startOffset="39" />
</Expression>
</Expressions>
<location endLine="33" endOffset="50" startLine="27" startOffset="8" />
</Target>
</Targets>
</Layout>第二个路径：app/build/incremental/mergeDebugResources/stripped.dir/layout下
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent" android:tag="layout/activity_data_bind_test_0" xmlns:android="http://schemas.android.com/apk/res/android">
<TextView
android:id="@+id/userName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:tag="binding_1"
android:textSize="20sp"/>
<TextView
android:id="@+id/userPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:tag="binding_2"
android:textSize="20sp"
/>
</LinearLayout>3.绑定布局时序
绑定布局咱们的入口是DataBinding类中的setContentView方法
public static <T extends ViewDataBinding> T setContentView(@NonNull Activity activity,
int layoutId, @Nullable DataBindingComponent bindingComponent) {
activity.setContentView(layoutId);
View decorView = activity.getWindow().getDecorView();
ViewGroup contentView = (ViewGroup) decorView.findViewById(android.R.id.content);
return bindToAddedViews(bindingComponent, contentView, 0, layoutId);
}
private static <T extends ViewDataBinding> T bindToAddedViews(DataBindingComponent component,
ViewGroup parent, int startChildren, int layoutId) {
final int endChildren = parent.getChildCount();
final int childrenAdded = endChildren - startChildren;
if (childrenAdded == 1) {
//只有一个子view
final View childView = parent.getChildAt(endChildren - 1);
return bind(component, childView, layoutId);
} else {
//存在多个子View
final View[] children = new View[childrenAdded];
for (int i = 0; i < childrenAdded; i++) {
children[i] = parent.getChildAt(i + startChildren);
}
return bind(component, children, layoutId);
}
}
static <T extends ViewDataBinding> T bind(DataBindingComponent bindingComponent, View[] roots,
int layoutId) {
return (T) sMapper.getDataBinder(bindingComponent, roots, layoutId);
}
static <T extends ViewDataBinding> T bind(DataBindingComponent bindingComponent, View root,
int layoutId) {
return (T) sMapper.getDataBinder(bindingComponent, root, layoutId);
}调用的也是activity的setContentView去显示布局，然后调用了bindToAddedViews方法去绑定添加View后续调用了bind方法。然后执行到bind方法中，里边调用的是sMapper.getDataBinder方法。DataBindingUtil中是这么设置sMapper的。
private static DataBinderMapper sMapper = new DataBinderMapperImpl();
private static DataBindingComponent sDefaultComponent = null;DataBinderMapperImpl刚才有生成这个文件。
public class DataBinderMapperImpl extends MergedDataBinderMapper {
DataBinderMapperImpl() {
addMapper(new com.example.kotlinweather.DataBinderMapperImpl());
}
}这个类构造方法中会调用addMapper去添加，参数是生成的另一个文件，仔细看类名哦，是项目包下的同名文件。我们看同名文件下的getDataBinder方法
@Override
public ViewDataBinding getDataBinder(DataBindingComponent component, View view, int layoutId) {
int localizedLayoutId = INTERNAL_LAYOUT_ID_LOOKUP.get(layoutId);
if(localizedLayoutId > 0) {
final Object tag = view.getTag();
if(tag == null) {
throw new RuntimeException("view must have a tag");
}
switch(localizedLayoutId) {
case LAYOUT_ACTIVITYDATABINDTEST: {
if ("layout/activity_data_bind_test_0".equals(tag)) {
return new ActivityDataBindTestBindingImpl(component, view);
}
throw new IllegalArgumentException("The tag for activity_data_bind_test is invalid. Received: " + tag);
}
}
}
return null;
}
@Override
public ViewDataBinding getDataBinder(DataBindingComponent component, View[] views, int layoutId) {
if(views == null || views.length == 0) {
return null;
}
int localizedLayoutId = INTERNAL_LAYOUT_ID_LOOKUP.get(layoutId);
if(localizedLayoutId > 0) {
final Object tag = views[0].getTag();
if(tag == null) {
throw new RuntimeException("view must have a tag");
}
switch(localizedLayoutId) {
}
}
return null;
}通过咱们生成的xml文件里的Tag来进行判断，来返回对应的ViewBinding对象。看生成的Impl文件
public ActivityDataBindTestBindingImpl(@Nullable androidx.databinding.DataBindingComponent bindingComponent, @NonNull View root) {
this(bindingComponent, root, mapBindings(bindingComponent, root, 3, sIncludes, sViewsWithIds));
}
private ActivityDataBindTestBindingImpl(androidx.databinding.DataBindingComponent bindingComponent, View root, Object[] bindings) {
super(bindingComponent, root, 1
, (android.widget.TextView) bindings[1]
, (android.widget.TextView) bindings[2]
);
this.mboundView0 = (android.widget.LinearLayout) bindings[0];
this.mboundView0.setTag(null);
this.userName.setTag(null);
this.userPassword.setTag(null);
setRootTag(root);
// listeners
invalidateAll();
}其中调用了mapBindings方法之后再请求了下边的构造方法。mapBindings
protected static Object[] mapBindings(DataBindingComponent bindingComponent, View root,
int numBindings, IncludedLayouts includes, SparseIntArray viewsWithIds) {
Object[] bindings = new Object[numBindings];
mapBindings(bindingComponent, root, bindings, includes, viewsWithIds, true);
return bindings;
}
private static void mapBindings(DataBindingComponent bindingComponent, View view,
Object[] bindings, IncludedLayouts includes, SparseIntArray viewsWithIds,
boolean isRoot) {
final int indexInIncludes;
final ViewDataBinding existingBinding = getBinding(view);
if (existingBinding != null) {
return;
}
Object objTag = view.getTag();
final String tag = (objTag instanceof String) ? (String) objTag : null;
boolean isBound = false;
if (isRoot && tag != null && tag.startsWith("layout")) {
//通过tag来判断是否为布局
final int underscoreIndex = tag.lastIndexOf('_');
//通过tag中的格式，最后一个下划线后的数字来存放view
if (underscoreIndex > 0 && isNumeric(tag, underscoreIndex + 1)) {
final int index = parseTagInt(tag, underscoreIndex + 1);
if (bindings[index] == null) {
bindings[index] = view;
}
indexInIncludes = includes == null ? -1 : index;
isBound = true;
} else {
indexInIncludes = -1;
}
} else if (tag != null && tag.startsWith(BINDING_TAG_PREFIX)) {
//通过tag来判断是否为binding_的view
//通过tag中的格式，最后一个下划线后的数字来存放view
int tagIndex = parseTagInt(tag, BINDING_NUMBER_START);
if (bindings[tagIndex] == null) {
bindings[tagIndex] = view;
}
isBound = true;
indexInIncludes = includes == null ? -1 : tagIndex;
} else {
// Not a bound view
indexInIncludes = -1;
}
if (!isBound) {
final int id = view.getId();
if (id > 0) {
int index;
if (viewsWithIds != null && (index = viewsWithIds.get(id, -1)) >= 0 &&
bindings[index] == null) {
bindings[index] = view;
}
}
}
if (view instanceof ViewGroup) {
//如果是布局文件，就遍历底下的子view
final ViewGroup viewGroup = (ViewGroup) view;
final int count = viewGroup.getChildCount();
int minInclude = 0;
for (int i = 0; i < count; i++) {
final View child = viewGroup.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('/') > 0) {
// This *could* be an include. Test against the expected includes.
int includeIndex = findIncludeIndex(childTag, minInclude,
includes, indexInIncludes);
if (includeIndex >= 0) {
isInclude = true;
minInclude = includeIndex + 1;
final int index = includes.indexes[indexInIncludes][includeIndex];
final int layoutId = includes.layoutIds[indexInIncludes][includeIndex];
int lastMatchingIndex = findLastMatching(viewGroup, i);
if (lastMatchingIndex == i) {
bindings[index] = DataBindingUtil.bind(bindingComponent, child,
layoutId);
} else {
final int includeCount = lastMatchingIndex - i + 1;
final View[] included = new View[includeCount];
for (int j = 0; j < includeCount; j++) {
included[j] = viewGroup.getChildAt(i + j);
}
bindings[index] = DataBindingUtil.bind(bindingComponent, included,
layoutId);
i += includeCount - 1;
}
}
}
}
if (!isInclude) {
//这个递归是咱们子View会生成的原因
mapBindings(bindingComponent, child, bindings, includes, viewsWithIds, false);
}
}
}
}返回了view数组后又调用了super，父类的构造方法。这个类继承自ActivityDataBindTestBinding，ActivityDataBindTestBinding中又调用了父类ViewDataBinding的构造方法。
protected ActivityDataBindTestBinding(Object _bindingComponent, View _root, int _localFieldCount,
TextView userName, TextView userPassword) {
super(_bindingComponent, _root, _localFieldCount);
this.userName = userName;
this.userPassword = userPassword;
} protected ViewDataBinding(Object bindingComponent, View root, int localFieldCount) {
this(checkAndCastToBindingComponent(bindingComponent), root, localFieldCount);
}
protected ViewDataBinding(DataBindingComponent bindingComponent, View root, int localFieldCount) {
mBindingComponent = bindingComponent;
mLocalFieldObservers = new WeakListener[localFieldCount];
this.mRoot = root;
if (Looper.myLooper() == null) {
throw new IllegalStateException("DataBinding must be created in view's UI Thread");
}
if (USE_CHOREOGRAPHER) {
mChoreographer = Choreographer.getInstance();
mFrameCallback = new Choreographer.FrameCallback() {
@Override
public void doFrame(long frameTimeNanos) {
mRebindRunnable.run();
}
};
} else {
mFrameCallback = null;
mUIThreadHandler = new Handler(Looper.myLooper());
}
}这一路的操作就把咱们的布局绑定到了ActivityDataBindTestBinding文件中，然后再viewDataBinding的构造方法中进行了渲染，通过sdk的比较，要么使用编舞者要么用线程来更新。编舞者的原理需要去了解FrameWork的Choregrapher类。
4.改变数据通知更新UI时序
这个入口是在生成的ViewBindingImpl文件中的set方法中，来看setUser
private long mDirtyFlags = 0xffffffffffffffffL;
public void setUser(@Nullable com.example.kotlinweather.ui.databin.User User) {
updateRegistration(0, User);
this.mUser = User;
synchronized(this) {
mDirtyFlags |= 0x1L;
}
notifyPropertyChanged(BR.user);
super.requestRebind();
}首先执行更新注册监听方法updateRegistration，然后用'脏标志'来或等于16进制的1.之后提示元素更改和请求渲染。
1.更新注册方法时序
private static final CreateWeakListener CREATE_PROPERTY_LISTENER = new CreateWeakListener() {
@Override
public WeakListener create(
ViewDataBinding viewDataBinding,
int localFieldId,
ReferenceQueue<ViewDataBinding> referenceQueue
) {
return new WeakPropertyListener(viewDataBinding, localFieldId, referenceQueue)
.getListener();
}
};
//根据传过来的元素继承什么，调用相应的注册方法 这里就不多粘出来了
protected boolean updateRegistration(int localFieldId, Observable observable) {
return updateRegistration(localFieldId, observable, CREATE_PROPERTY_LISTENER);
}
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
protected boolean updateRegistration(int localFieldId, Object observable,
CreateWeakListener listenerCreator) {
//如果数据为空就注销这个注册
if (observable == null) {
return unregisterFrom(localFieldId);
}
//mLocalFieldObservers这个参数在ViewDataBinding构造方法中有初始化
//mLocalFieldObservers = new WeakListener[localFieldCount];
WeakListener listener = mLocalFieldObservers[localFieldId];
if (listener == null) {
//注册
registerTo(localFieldId, observable, listenerCreator);
return true;
}
//判断是否为一个对象
if (listener.getTarget() == observable) {
return false;//nothing to do, same object
}
//相应的监听listener存在且值有改变就先注销再重新
unregisterFrom(localFieldId);
registerTo(localFieldId, observable, listenerCreator);
return true;
}
protected void registerTo(int localFieldId, Object observable,
CreateWeakListener listenerCreator) {
//再次判断咱们的对象user是否为空
if (observable == null) {
return;
}
WeakListener listener = mLocalFieldObservers[localFieldId];
if (listener == null) {
//这里的this 指的是对应的ViewDataBinding对象
//得到的listener 根据上边传的值 返回的是WeakPropertyListener.getlistener的WeakListener类
listener = listenerCreator.create(this, localFieldId, sReferenceQueue);
mLocalFieldObservers[localFieldId] = listener;
//如果你的被观察者存在那么就订阅，默认咱们是没有的。需要手动的调用viewDataBinding.setLifecycleOwner才会调用if内的订阅
if (mLifecycleOwner != null) {
listener.setLifecycleOwner(mLifecycleOwner);
}
}
//上面说了返回的会是WeakListener的
listener.setTarget(observable);
}
这样咱们就来看WeakPropertyListener和WeakListener。
private static class WeakPropertyListener extends Observable.OnPropertyChangedCallback
implements ObservableReference<Observable> {
final WeakListener<Observable> mListener;
public WeakPropertyListener(
ViewDataBinding binder,
int localFieldId,
ReferenceQueue<ViewDataBinding> referenceQueue
) {
//此listener代表的是WeakPropertyListener
mListener = new WeakListener<Observable>(binder, localFieldId, this, referenceQueue);
}
@Override
public WeakListener<Observable> getListener() {
return mListener;
}
@Override
public void addListener(Observable target) {
//这边的target是咱们的User，从WeakListener中传出来的，咱们User继承自BaseObservable
target.addOnPropertyChangedCallback(this);
}
......
}
class WeakListener<T> extends WeakReference<ViewDataBinding> {
private final ObservableReference<T> mObservable;
protected final int mLocalFieldId;
private T mTarget;//存放咱们的User对象
public WeakListener(
ViewDataBinding binder,
int localFieldId,
ObservableReference<T> observable,
ReferenceQueue<ViewDataBinding> referenceQueue
) {
//去父类的构造方法，存着咱们对应的viewDataBinding对象
super(binder, referenceQueue);
mLocalFieldId = localFieldId;
mObservable = observable;
}
public void setTarget(T object) {
unregister();
mTarget = object;
if (mTarget != null) {
//这个mObservable是刚才的listener-WeakPropertyListener
mObservable.addListener(mTarget);
}
}
......
}listener最后存放的是WeakListener。因为他即持有着咱们的viewDataBinding，还持有着User对象。以上最后走到了BaseObservable对象的addOnPropertyChangedCallback方法。接下去看
private transient PropertyChangeRegistry mCallbacks;
@Override
public void addOnPropertyChangedCallback(@NonNull OnPropertyChangedCallback callback) {
synchronized (this) {
if (mCallbacks == null) {
mCallbacks = new PropertyChangeRegistry();
}
}
//这里的callback是咱们上面传下来的WeakPropertyListener，他继承于OnPropertyChangedCallback
mCallbacks.add(callback);
}最后这个add方法是CallbackRegistry里的
private List<C> mCallbacks = new ArrayList<C>();
public synchronized void add(C callback) {
if (callback == null) {
throw new IllegalArgumentException("callback cannot be null");
}
int index = mCallbacks.lastIndexOf(callback);
if (index < 0 || isRemoved(index)) {
mCallbacks.add(callback);
}
}这样咱们就存放了我们的注册监听在callbacks中。
2.提示元素更改（notifyPropertyChanged）
ViewDataBinding也是继承自BaseObservable的，所以调用此方法时就到了BaseObservable中的此方法。
private transient PropertyChangeRegistry mCallbacks;
public void notifyPropertyChanged(int fieldId) {
synchronized (this) {
if (mCallbacks == null) {
return;
}
}
//这个mCallbacks咱们再注册时序时看过，是PropertyChangeRegistry类
mCallbacks.notifyCallbacks(this, fieldId, null);
}
//再次回顾一下这个方法
@Override
public void addOnPropertyChangedCallback(@NonNull OnPropertyChangedCallback callback) {
synchronized (this) {
if (mCallbacks == null) {
mCallbacks = new PropertyChangeRegistry();
}
}
mCallbacks.add(callback);
}因为我们的ViewDataBinding没有执行过addOnPropertyChangedCallback方法所以会执行return，之前执行addOnPropertyChangedCallback方法是User类！不能搞错
3.更新控件UI
其实无论是高版本还是低版本，刷新UI都是mRebindRunnable
protected void requestRebind() {
if (mContainingBinding != null) {
mContainingBinding.requestRebind();
} else {
final LifecycleOwner owner = this.mLifecycleOwner;
if (owner != null) {
//判断是否为显示中
Lifecycle.State state = owner.getLifecycle().getCurrentState();
if (!state.isAtLeast(Lifecycle.State.STARTED)) {
return; // wait until lifecycle owner is started
}
}
synchronized (this) {
if (mPendingRebind) {
return;
}
mPendingRebind = true;
}
if (USE_CHOREOGRAPHER) {
mChoreographer.postFrameCallback(mFrameCallback);
} else {
mUIThreadHandler.post(mRebindRunnable);
}
}
}
//在构造方法中有初始化mFrameCallback
protected ViewDataBinding(DataBindingComponent bindingComponent, View root, int localFieldCount) {
mBindingComponent = bindingComponent;
mLocalFieldObservers = new WeakListener[localFieldCount];
if (USE_CHOREOGRAPHER) {
mChoreographer = Choreographer.getInstance();
mFrameCallback = new Choreographer.FrameCallback() {
@Override
public void doFrame(long frameTimeNanos) {
mRebindRunnable.run();
}
};
} else {
mFrameCallback = null;
mUIThreadHandler = new Handler(Looper.myLooper());
}
}mRebindRunnable
private final Runnable mRebindRunnable = new Runnable() {
@Override
public void run() {
......
executePendingBindings();
}
};
public void executePendingBindings() {
//这里判断是否为空，否则递归调用知道为空 执行Internal
if (mContainingBinding == null) {
executeBindingsInternal();
} else {
mContainingBinding.executePendingBindings();
}
}
private void executeBindingsInternal() {
if (mIsExecutingPendingBindings) {
requestRebind();
return;
}
if (!hasPendingBindings()) {
return;
}
mIsExecutingPendingBindings = true;
mRebindHalted = false;
if (mRebindCallbacks != null) {
mRebindCallbacks.notifyCallbacks(this, REBIND, null);
// The onRebindListeners will change mPendingHalted
if (mRebindHalted) {
mRebindCallbacks.notifyCallbacks(this, HALTED, null);
}
}
if (!mRebindHalted) {
//刷新ui
executeBindings();
if (mRebindCallbacks != null) {
mRebindCallbacks.notifyCallbacks(this, REBOUND, null);
}
}
mIsExecutingPendingBindings = false;
}
protected abstract void executeBindings();执行到了executeBindings方法，这个方法是个抽象方法，就需要我们自己对应的viewDataBinding里看。
@Override
protected void executeBindings() {
long dirtyFlags = 0;
synchronized(this) {
dirtyFlags = mDirtyFlags;
mDirtyFlags = 0;
}
java.lang.String UserName1 = null;
com.example.kotlinweather.ui.databin.User user = mUser;
java.lang.String UserPassword1 = null;
if ((dirtyFlags & 0x39L) != 0) {
if ((dirtyFlags & 0x29L) != 0) {
if (user != null) {
// read user.name
UserName1 = user.getName();
}
}
if ((dirtyFlags & 0x31L) != 0) {
if (user != null) {
// read user.password
UserPassword1 = user.getPassword();
}
}
}
// batch finished
if ((dirtyFlags & 0x29L) != 0) {
// api target 1
//在这里设置了我们的ui
androidx.databinding.adapters.TextViewBindingAdapter.setText(this.userName, UserName1);
}
if ((dirtyFlags & 0x31L) != 0) {
// api target 1
//在这里设置了我们的ui
androidx.databinding.adapters.TextViewBindingAdapter.setText(this.userPassword, UserPassword1);
}
}4.脏标记判断
上关键位置的代码（首次刷新UI）的代码。
private long mDirtyFlags = 0xffffffffffffffffL;
@Override
protected void executeBindings() {
long dirtyFlags = 0;
synchronized(this) {
dirtyFlags = mDirtyFlags;
mDirtyFlags = 0;
}
java.lang.String UserName1 = null;
com.example.kotlinweather.ui.databin.User user = mUser;
java.lang.String UserPassword1 = null;
......
if ((dirtyFlags & 0x39L) != 0) {
if ((dirtyFlags & 0x29L) != 0) {
if (user != null) {
// read user.name
UserName1 = user.getName();
}
}
if ((dirtyFlags & 0x31L) != 0) {
if (user != null) {
// read user.password
UserPassword1 = user.getPassword();
}
}
}
// batch finished
if ((dirtyFlags & 0x29L) != 0) {
// api target 1
androidx.databinding.adapters.TextViewBindingAdapter.setText(this.userName, UserName1);
}
if ((dirtyFlags & 0x31L) != 0) {
// api target 1
androidx.databinding.adapters.TextViewBindingAdapter.setText(this.userPassword, UserPassword1);
}
......
}因为这个运算是二进制，用二进制看。首次进入的时候我们的‘脏标记’是0xffffffffL,因为BR文件长度6位，咱们二进制只取6位即可。
| 十六进制 | 二进制 | 和脏数据&的结果 |
| 0xffL | 11 1111 | 本身就是脏数据 |
| 0x39L | 11 1001 | 结果是本身 |
| 0x29L | 10 1001 | 结果是本身 |
| 0x31L | 11 0001 | 结果是本身 |
与操作的逻辑是：0&0=0；0&1=0；1&0=0；1&1=1。所以第一次进来都会被setText。然后全局的脏数据mDirtyFlags 赋值给方法内脏布局后清零。
5.重看提示元素更改（notifyPropertyChanged）
activity的方法我加了一行。
binding.listener = View.OnClickListener {
user.password += "1"
}那为什么我改变password的值UI能够跟着改变呢？
var password = userPassword
@Bindable
get() = field
set(value) {
field = value
notifyPropertyChanged(BR.password)
}因为set方法中存在着notifyPropertyChanged这个方法提示元素更改。
public class BaseObservable implements Observable {
private transient PropertyChangeRegistry mCallbacks;
@Override
public void addOnPropertyChangedCallback(@NonNull OnPropertyChangedCallback callback) {
synchronized (this) {
if (mCallbacks == null) {
mCallbacks = new PropertyChangeRegistry();
}
}
mCallbacks.add(callback);
}
public void notifyPropertyChanged(int fieldId) {
synchronized (this) {
if (mCallbacks == null) {
return;
}
}
mCallbacks.notifyCallbacks(this, fieldId, null);
}
}这代码是我贴出来的第三次了，应该很有印象了。 第一次注册时，使用的mOberverble是咱们setUser的user对象，所以调用addOnPropertyChangedCallback方法就得到了后续的注册，这个callback是当时的WeakPropertyListener监听。而viewDataBinding没有执行过所以判空时直接返回了。所以User执行不会为空，看后续的调用。我快进一些，后续调用的方法比较多。
public class PropertyChangeRegistry extends
CallbackRegistry<Observable.OnPropertyChangedCallback, Observable, Void> {
private static final CallbackRegistry.NotifierCallback<Observable.OnPropertyChangedCallback, Observable, Void> NOTIFIER_CALLBACK = new CallbackRegistry.NotifierCallback<Observable.OnPropertyChangedCallback, Observable, Void>() {
@Override
public void onNotifyCallback(Observable.OnPropertyChangedCallback callback, Observable sender,
int arg, Void notUsed) {
callback.onPropertyChanged(sender, arg);//之前的callback是WeakPropertyListener。调用的是它的方法
}
};
public PropertyChangeRegistry() {
super(NOTIFIER_CALLBACK);
}
/**
* Notifies registered callbacks that a specific property has changed.
*
* @param observable The Observable that has changed.
* @param propertyId The BR id of the property that has changed or BR._all if the entire
* Observable has changed.
*/
public void notifyChange(@NonNull Observable observable, int propertyId) {
notifyCallbacks(observable, propertyId, null);
}
}经过一系列跳转后，会执行NOTIFIER_CALLBACK变量中的onNotifyCallback方法。然后就调用了WeakPropertyListener.onPropertyChanged()方法
private static class WeakPropertyListener extends Observable.OnPropertyChangedCallback
implements ObservableReference<Observable> {
final WeakListener<Observable> mListener;
@Override
public void onPropertyChanged(Observable sender, int propertyId) {
ViewDataBinding binder = mListener.getBinder();
if (binder == null) {
return;
}
Observable obj = mListener.getTarget();
if (obj != sender) {
return; // notification from the wrong object?
}
binder.handleFieldChange(mListener.mLocalFieldId, sender, propertyId);
}
}咱们的listener持有着viewDataBinding和User的对象，get到对应的viewDataBinding对象后执行handleFieldChange方法。
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
protected void handleFieldChange(int mLocalFieldId, Object object, int fieldId) {
if (mInLiveDataRegisterObserver || mInStateFlowRegisterObserver) {
// We're in LiveData or StateFlow registration, which always results in a field change
// that we can ignore. The value will be read immediately after anyway, so
// there is no need to be dirty.
return;
}
boolean result = onFieldChange(mLocalFieldId, object, fieldId);
if (result) {
requestRebind();
}
}onFieldChange方法是判断其是否有做变化。有变化就requestRebind方法刷新页面，这个方法上边看过这边就不重复看了。
@Override
protected boolean onFieldChange(int localFieldId, Object object, int fieldId) {
switch (localFieldId) {
case 0 :
return onChangeUser((com.example.kotlinweather.ui.databin.User) object, fieldId);
}
return false;
}
private boolean onChangeUser(com.example.kotlinweather.ui.databin.User User, int fieldId) {
if (fieldId == BR._all) {
synchronized(this) {
mDirtyFlags |= 0x1L;
}
return true;
}
else if (fieldId == BR.name) {
synchronized(this) {
mDirtyFlags |= 0x8L;
}
return true;
}
else if (fieldId == BR.password) {
synchronized(this) {
mDirtyFlags |= 0x10L;
}
return true;
}
return false;
}这边是或运算，改变‘脏标记’的值，这样最后执行executeBindings方法的时候能够保证其通过判断然后刷新ui。
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