編輯:關於Android編程
如何高效地實現以下界面?
vc23z/FJbWFnZVZpZXehorHqzOJUZXh0Vmlld6Giu/231lRleHRWaWV3oaK1x8K8QnV0dG9uo6zIu7rzuPhCdXR0b27J6NbDvODM/cb3o6zU2bj5vt21x8K917TMrNW5yr621NOmyv2+3aO7PC9wPg0KPHA+yrXP1sjnz8KjujxiciAvPg0KKiBVc2VyLmphdmE8L3A+DQo8cHJlIGNsYXNzPQ=="brush:java;">
public class User {
private String name;
private int score;
private int level;
private int avatar;
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public int getScore() { return score; }
public void setScore(int score) { this.score = score; }
public int getLevel() { return level; }
public int getAvatar() { return avatar; }
public void setAvatar(int avatar) { this.avatar = avatar; }
public void setLevel(int level) { this.level = level; }
public static User newInstance() {
User user = new User();
user.setName("王大錘:" + (int)(Math.random() * 10));
user.setScore((int) (Math.random() * 999));
user.setLevel((int) (Math.random() * 77));
user.setAvatar(R.drawable.avatar);
return user;
}
}
activity_detail.xml
DetailActivity
public class DetailActivity extends AppCompatActivity {
ImageView avatarIV;
TextView nameTV;
TextView descTV;
Button actionBtn;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
initView();
login();
}
private void login(){ fill(User.newInstance()); }
private void logout(){ fill(null); }
private void initView() {
avatarIV = (ImageView) findViewById(R.id.detail_avatar);
nameTV = (TextView) findViewById(R.id.detail_name);
descTV = (TextView) findViewById(R.id.detail_desc);
actionBtn = (Button) findViewById(R.id.detail_action_button);
}
private void fill(final User user){
final int visibility = user != null ? View.VISIBLE : View.GONE;
if (avatarIV != null){
avatarIV.setVisibility(visibility);
if (user != null)
avatarIV.setImageDrawable(ContextCompat.getDrawable(this,user.getAvatar()));
}
if (nameTV != null){
nameTV.setVisibility(visibility);
if (user != null)
nameTV.setText(user.getName());
}
if (descTV != null){
descTV.setVisibility(visibility);
if (user != null)
descTV.setText(String.format("積分:%d 等級:%d",user.getScore(),user.getLevel()));
}
if (actionBtn != null){
actionBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (user == null) login();
else logout();
}
});
actionBtn.setText(user == null ? "登錄":"退出登錄");
}
}
}
可以看到,在Activity中View的定義、find、判空占據了大量篇幅,我們需要更優雅的實現。
你可能聽說過Jake Wharton的ButterKnife,這個庫只需要在定義View變量的時候通過注解傳入對應id,隨後在onCreate時調用ButterKnife.bind(this)
即可完成view的注入,示例如下:
class ExampleActivity extends Activity {
@BindView(R.id.user) EditText username;
@BindView(R.id.pass) EditText password;
@Override public void onCreate(Bundle savedInstanceState{
super.onCreate(savedInstanceState);
setContentView(R.layout.simple_activity);
ButterKnife.bind(this);
}
}
如果使用了Android Data Binding,那麼View的定義、find、判空這些都不用寫了,如何做呢?
首先,你需要滿足一個條件:你的Android Plugin for Gradle
版本必須等於或高於1.5.0-alpha1版本,這個版本位於根目錄build.gradle
中,示例如下:
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:2.1.0-rc1'
}
}
接著,你必須告訴編譯器開啟Data Binding,一般位於app:build.gradle
的android標簽中,示例如下:
android {
compileSdkVersion 23
buildToolsVersion "23.0.2"
dataBinding {
enabled true
}
...
}
以activity_detail.xml
為例,原來的根節點為LinearLayout
,如下所示:
....
我們拷一份activity_detail.xml
,改為activity_detail2.xml
,並且需要在外面wrap一層layout標簽,修改後的activity_detail2.xml
為:
...
在上述操作完成後,編譯器會自動為我們生成
com.asha.demo.databinding.ActivityDetail2Binding.java
類,這個類的命令方式為:包名 + databinding + activity_detail2駝峰命名方式 + Binding.java。隨後,使用這個activity_detail2
的DetailActivity2.java
的代碼可以簡化為:
public class DetailActivity2 extends AppCompatActivity {
ActivityDetail2Binding binding;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(this,R.layout.activity_detail2);
login();
}
private void login(){ fill(User.newInstance()); }
private void logout(){ fill(null); }
private void fill(final User user){
final int visibility = user != null ? View.VISIBLE : View.GONE;
if (user != null){
binding.detailAvatar.setImageDrawable(ContextCompat.getDrawable(this,user.getAvatar()));
binding.detailName.setText(user.getName());
binding.detailDesc.setText(String.format("積分:%d 等級:%d",user.getScore(),user.getLevel()));
}
binding.detailAvatar.setVisibility(visibility);
binding.detailName.setVisibility(visibility);
binding.detailDesc.setVisibility(visibility);
binding.detailActionButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (user == null) login();
else logout();
}
});
binding.detailActionButton.setText(user == null ? "登錄":"退出登錄");
}
}
是的,所有View的定義、find、判空都不見了,所有的這些操作都在編譯器為我們生成的ActivityDetail2Binding.java
中完成,只需要在onCreate時調用如下代碼進行setContentView即可實現,
binding = DataBindingUtil.setContentView(this,R.layout.activity_detail2);
可以在as中方便的查看編譯器自動生成的類,這個類位於/app/build/intermediates/classes/debug/com/asha/demo/databinding/ActivityDetail2Binding.class中,縮減掉Binding邏輯後的代碼為:
public class ActivityDetail2Binding extends ViewDataBinding {
private static final IncludedLayouts sIncludes = null;
private static final SparseIntArray sViewsWithIds = new SparseIntArray();
public final Button detailActionButton;
public final ImageView detailAvatar;
public final TextView detailDesc;
public final TextView detailName;
private final LinearLayout mboundView0;
private long mDirtyFlags = -1L;
public ActivityDetail2Binding(DataBindingComponent bindingComponent, View root) {
super(bindingComponent, root, 0);
Object[] bindings = mapBindings(bindingComponent, root, 5, sIncludes, sViewsWithIds);
this.detailActionButton = (Button)bindings[4];
this.detailAvatar = (ImageView)bindings[1];
this.detailDesc = (TextView)bindings[3];
this.detailName = (TextView)bindings[2];
this.mboundView0 = (LinearLayout)bindings[0];
this.mboundView0.setTag((Object)null);
this.setRootTag(root);
this.invalidateAll();
}
...
static {
sViewsWithIds.put(2131492948, 1);
sViewsWithIds.put(2131492949, 2);
sViewsWithIds.put(2131492950, 3);
sViewsWithIds.put(2131492951, 4);
}
}
其中全局靜態SparseIntArray數組中存放了4個數字,這個四個數字為R.java中生成的對應View的id,
public final class R {
...
public static final class id {
...
public static final int detail_action_button = 2131492951;
public static final int detail_avatar = 2131492948;
public static final int detail_desc = 2131492950;
public static final int detail_name = 2131492949;
...
}
...
}
在ActvityDetail2Binding
實例構造的時候調用了mapBindings
,一次解決了所有View的查找,mapBindings
函數在ActvityDetail2Binding
父類ViewDataBinding
中實現。
在ActivityDetail2.java
中還存在大量的View控制、數據填充代碼,如何把這些代碼在交給layout.xml
完成呢?
第2節中已經定義了User.java類作為Model類,但是我們經常會遇到Model類和真正View展示不一致的情況,本例子中定義一個來ModelAdapter類來完整Model數據到展示數據的適配。示例代碼為ActivityDetail3.java
的內部類,可以調用ActivityDetail3.java
中的函數,代碼定義如下:
public class DetailActivity3 extends AppCompatActivity {
public class ModelAdapter {
private User user;
public ModelAdapter(User user) { this.user = user;}
public String getName(){ return user != null ? user.getName() : null;}
public Drawable getAvatar(){
return user != null ? ContextCompat.getDrawable(DetailActivity3.this,user.getAvatar()) : null;
}
public String getDesc(){
return user != null ? String.format("積分:%d 等級:%d",user.getScore(),user.getLevel()) : null;
}
public String actionText(){ return user != null ? "退出登錄" : "登陸"; }
public void clickHandler(View view){
if (user != null) logout();
else login();
}
}
}
同樣復制一份activity_detail2.xml
為activity_detail3.xml
,在
節點加入節點,並且在裡面定義需要用的model類(比如ModelAdapter adapter),當然也可以是基礎類型變量(比如int visibility);
隨後,就可以在下面的view中使用表達式了,全部布局文件如下:
如下代碼所示,只需要在登錄狀態改變的時候,給viewDataBinding設置所需要的adatper、visibility值,即可完成數據的填充
public class DetailActivity3 extends AppCompatActivity {
ActivityDetail3Binding binding;
public class ModelAdapter {
...
}
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(this,R.layout.activity_detail3);
login();
}
private void login(){
fill(User.newInstance());
}
private void logout(){
fill(null);
}
private void fill(final User user){
binding.setAdapter(new ModelAdapter(user));
binding.setVisibility( user != null ? View.VISIBLE : View.GONE);
}
}
同樣,ActivityDetail3Binding中,編譯器根據activity_detail3.xml
中的標簽,自動生成了諸如setAdapter、setVisibility的代碼,setAdapter相關代碼如下:
public class ActivityDetail3Binding extends ViewDataBinding{
private ModelAdapter mAdapter;
...
public void setAdapter(ModelAdapter adapter) {
this.mAdapter = adapter;
synchronized(this) {
this.mDirtyFlags |= 1L;
}
this.notifyPropertyChanged(1);
super.requestRebind();
}
public ModelAdapter getAdapter() {
return this.mAdapter;
}
...
}
非常簡單,自動生成了getter和setter,在完成set操作後,調用執行notifyPropertyChanged
和super.requestRebind()
* notifyPropertyChanged
ViewDataBinding本身就是一個BaseObservable, 在往ViewDataBinding注冊觀察某個屬性的變化,如果注冊了mAdapter的變化,對應的觀察器就會接收到回調。相關邏輯與反向Binding相關,谷歌官方還沒給出相關使用文檔,不再深入分析;
public abstract class ViewDataBinding extends BaseObservable {
protected void requestRebind() {
synchronized (this) {
if (mPendingRebind) {
return;
}
mPendingRebind = true;
}
if (USE_CHOREOGRAPHER) {
mChoreographer.postFrameCallback(mFrameCallback);
} else {
mUIThreadHandler.post(mRebindRunnable);
}
}
/**
* Runnable executed on animation heartbeat to rebind the dirty Views.
*/
private final Runnable mRebindRunnable = new Runnable() {
@Override
public void run() {
synchronized (this) {
mPendingRebind = false;
}
if (VERSION.SDK_INT >= VERSION_CODES.KITKAT) {
// Nested so that we don't get a lint warning in IntelliJ
if (!mRoot.isAttachedToWindow()) {
// Don't execute the pending bindings until the View
// is attached again.
mRoot.removeOnAttachStateChangeListener(ROOT_REATTACHED_LISTENER);
mRoot.addOnAttachStateChangeListener(ROOT_REATTACHED_LISTENER);
return;
}
}
executePendingBindings();
}
};
}
3.在父類ViewDataBinding
中經過一些的判斷,調用到ActivityDetail3Binding
中的executeBindings
,在executeBindings
中根據dirtyFlags執行不同的View屬性賦值,以下所有ActivityDetail3Binding
相關代碼都是編譯器自動生成的
public class ActivityDetail3Binding extends ViewDataBinding{
...
protected void executeBindings() {
long dirtyFlags = 0L;
synchronized(this) {
dirtyFlags = this.mDirtyFlags;
this.mDirtyFlags = 0L;
}
Drawable avatarAdapter = null;
ModelAdapter adapter = this.mAdapter;
String descAdapter = null;
String nameAdapter = null;
ActivityDetail3Binding.OnClickListenerImpl androidViewViewOnCli = null;
String actionTextAdapter = null;
int visibility = this.mVisibility;
if((dirtyFlags & 5L) != 0L && adapter != null) {
avatarAdapter = adapter.getAvatar();
descAdapter = adapter.getDesc();
nameAdapter = adapter.getName();
androidViewViewOnCli = (this.mAndroidViewViewOnCl == null?(this.mAndroidViewViewOnCl = new ActivityDetail3Binding.OnClickListenerImpl()):this.mAndroidViewViewOnCl).setValue(adapter);
actionTextAdapter = adapter.actionText();
}
if((dirtyFlags & 6L) != 0L) {
;
}
if((dirtyFlags & 5L) != 0L) {
TextViewBindingAdapter.setText(this.detailActionButton, actionTextAdapter);
this.detailActionButton.setOnClickListener(androidViewViewOnCli);
ImageViewBindingAdapter.setImageDrawable(this.detailAvatar, avatarAdapter);
TextViewBindingAdapter.setText(this.detailDesc, descAdapter);
TextViewBindingAdapter.setText(this.detailName, nameAdapter);
}
if((dirtyFlags & 6L) != 0L) {
this.detailAvatar.setVisibility(visibility);
this.detailDesc.setVisibility(visibility);
this.detailName.setVisibility(visibility);
}
}
...
}
至此,完成了View數據的填充分析。
自動生成的ViewDataBinding類(例如ActivityDetail3Binding)內包含了Model + View,是MVVM中的MV的概念。
第2章的View注入,第3章的View賦值都是鋪墊,他們最後都是為Binding操作進行服務。目前谷歌已經支持雙向Binding,但上文已經提到,目前資料比較少。本文只關注單向的Binding,即:Model的變化,自動同步到View上。
目前所提供的ObservableField有:
本文使用簡單的ObservableInt作為示例,解決visibility的單項綁定問題。
* 改造activity_detail4.xml:定義類型為ObservableInt的variable,name為visibility,隨後賦值給ImageView的android:visibility
,示例如下:
...
...
改造DetailActivity4.java
,只需要在onCreate時把visibility
賦值給binding(ActivityDetail4Binding)即可,後面對visibility的操作,就會更新到view上,示例代碼如下:
public class DetailActivity4 extends AppCompatActivity {
ActivityDetail4Binding binding;
ObservableInt visibility = new ObservableInt();
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(this,R.layout.activity_detail4,new MyComponent());
binding.setVisibility(visibility);
login();
}
private void login(){ fill(User.newInstance()); }
private void logout(){ fill(null); }
private void fill(final User user){
visibility.set(user != null ? View.VISIBLE : View.GONE);
....
}
....
}
與給ActivityDetail4Binding直接set純Model不同,所有的ObservableField都實現了Observable接口,只要實現了Observable接口,都是單向Binding類型,所以ActivityDetail4Binding中的setVisibility
多加了一行代碼:this.updateRegistration(1, visibility)
,其中1為propertyId,目前一共自動生成了2個,0為adatper,1為visibility,代碼如下:
public class ActivityDetail4Binding extends ViewDataBinding {
...
public void setVisibility(ObservableInt visibility) {
this.updateRegistration(1, visibility);
this.mVisibility = visibility;
synchronized(this) {
this.mDirtyFlags |= 2L;
}
this.notifyPropertyChanged(3);
super.requestRebind();
}
...
}
updateRegistration函數為ViewDataBinding
中的函數,會根據 Observable、ObservableList、ObservableMap三種類型,分別創建對應的Listener。ObservableInt為Observable,所以會使用CREATE_PROPERTY_LISTENER,在registerTo
函數中創建WeakPropertyListener
,
代碼如下:
public abstract class ViewDataBinding extends BaseObservable {
...
private boolean updateRegistration(int localFieldId, Object observable,
CreateWeakListener listenerCreator) {
if (observable == null) {
return unregisterFrom(localFieldId);
}
WeakListener listener = mLocalFieldObservers[localFieldId];
if (listener == null) {
registerTo(localFieldId, observable, listenerCreator);
return true;
}
if (listener.getTarget() == observable) {
return false;//nothing to do, same object
}
unregisterFrom(localFieldId);
registerTo(localFieldId, observable, listenerCreator);
return true;
}
...
}
在WeakPropertyListener的mListener有個setTarget函數
,這個函數會向mObservable(即外面傳進來的visibility)注冊一個監聽器,如果visibility值發生變化,這個listener就會得到通知,回調到WeakPropertyListener
的onPropertyChanged
,接著通知到binding(ActivityDetail4Binding)的handleFieldChange
,在handleFieldChange
中調用了ActivityDetail4Binding
的onFieldChange
函數,如果返回值為true,則在handleFieldChange
中調用requestRebind()
,通知View進行賦值更新界面,onFieldChange
相關代碼如下:
public abstract class ViewDataBinding extends BaseObservable {
...
private void handleFieldChange(int mLocalFieldId, Object object, int fieldId) {
boolean result = onFieldChange(mLocalFieldId, object, fieldId);
if (result) {
requestRebind();
}
}
...
}
public class ActivityDetail4Binding extends ViewDataBinding {
...
protected boolean onFieldChange(int localFieldId, Object object, int fieldId) {
switch(localFieldId) {
case 0:
return this.onChangeAdapter((ModelAdapter)object, fieldId);
case 1:
return this.onChangeVisibility((ObservableInt)object, fieldId);
default:
return false;
}
}
...
}
與4.1 ObservableField類似,可以改造一下ModelAdapter
:為getter方法增加@Bindable
注解,為setter方法增加notifyPropertyChanged(com.asha.demo.BR.name)
通知。其中,BR是根據@Bindalbe
自動生成的類,給getter方法增加@Bindable
注解後,BR文件自動會生成一個整型的name。改造後代碼如下:
public class DetailActivity4 extends AppCompatActivity {
ActivityDetail4Binding binding;
ObservableInt visibility = new ObservableInt();
public class ModelAdapter extends BaseObservable{
private User user;
public ModelAdapter(User user) {
this.user = user;
}
...
@Bindable
public String getName(){
return user != null ? user.getName() : null;
}
public void setName(String name){
if (user != null) user.setName(name);
notifyPropertyChanged(com.asha.demo.BR.name);
}
...
}
...
}
隨後,在DetailActivity4.java中調用測試代碼,執行完會在1秒後改變adapter上的name值,並且同步到View上,測試代碼如下:
binding.detailActionButton.postDelayed(new Runnable() {
@Override
public void run() {
adapter.setName("haha");
}
},1000);
具體原理與4.1類似,不再贅述。
在下述示例中,detail_name這個TextView想把adapter.name賦值給自身的text屬性,就需要調用textView.setText(String)
方法,這個方法就是View屬性的setter方法。
上述的setter方法,Data Binding庫幫我們實現了大部分默認方法,具體方法參見android.databinding.adapters包下的類,下圖為ViewBindingAdatper具體實現,
其中setter方法都為static方法,第一個參數都為自身的實例,後面為xml中傳入的參數,只要加入@BindingAdapter注解,編譯器就會全局搜索保存在一個temp文件中,並在生成類似ActivityDetail4Binding
過程中去查找所需的setter方法的。如果需要自定義,只需要在任意app代碼中定義@BindingAdapter即可,例如:
public class DetailActivity4 extends AppCompatActivity {
@BindingAdapter("android:alpha")
public static void globalSetAlpha(View view, float alpha) {
view.setAlpha(alpha);
}
}
很多情況下只是某個Binding文件(例如ActivityDetail4Binding)需要自定義setter方法,這個時候就需要使用DataBindingComponent,
* 首先,定義一個MyComponent,
public class MyComponent implements android.databinding.DataBindingComponent {
@BindingAdapter("android:alpha")
public void setAlpha(View view, float alpha) {
view.setAlpha(0.5f);
}
@Override
public MyComponent getMyComponent() {
return new MyComponent();
}
}
接著,在生成Binding對象時傳入這個DataBindingComponent實例,代碼如下:
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = DataBindingUtil.setContentView(this,R.layout.activity_detail4,new MyComponent());
...
}
完成後,這個ActivityDetail4Binding范圍內的所有android:alpha="@{foo}"
的方式賦值alpha的setter函數都會使用MyComponent#setAlpha
。
有時候會遇到類型不匹配的問題,比如R.color.white是int,但是通過Data Binding賦值給android:background
屬性後,需要把int轉換為ColorDrawable,實現方式如下:
* 1.定義一個靜態函數,放在項目任意類中,
@BindingConversion
public static Drawable convertColorToDrawable(int drawable) {
return new ColorDrawable(drawable);
}
2.在layout.xml中使用Data Binding,如:
對應在ActivityDetail4Binding.java中生成的代碼如下所示,其中AvatarAdapterObjectn1
為int類型:
ViewBindingAdapter.setBackground(this.mboundView1, DetailActivity4.convertColorToDrawable(AvatarAdapterObjectn1));
例如layout.xml中android:onClick
屬性,在Binding中真正使用setter時,就對應到了setOnClickListener
方法,
@BindingMethod(type = View.class, attribute = "android:onClick", method = "setOnClickListener"),
Data Binding相關的jar包由四部分組成,
* 1.baseLibrary-2.1.0-rc1.jar
作為運行時類庫被打進APK中;
2.DataBinderPlugin(gradle plugin)
在編譯期使用,利用gradle-api(之前叫transform-api,1.5生,2.0改名)處理xml文件,生成DataBindingInfo.java;
3.compiler-2.1.0-rc1.jar
在編譯器使用,入口類繼承自AbstractProcessor,用於處理注解,並生成Binding類,DataBindingCompoent.java,DataBinderMapper.java類;
4.compilerCommon-2.1.0-rc1.jar
被DataBinderPlugin
和compiler-2.1.0-rc1.jar
所依賴
為了提高運行時的效率,Data Binding在背後做了非常多的工作,下圖是我整理的編譯流程,如圖所示:
白色部分為輸入,包括
1.res/layout;
2.源代碼中的注解;
黃色部分為編譯器處理類,包括
1.aapt編譯時處理,入口類名為MakeCopy.java
;
2.gradle-api處理,入口類名為DataBinderPlugin.java
;
3.AbstractProcessor處理,入口類名為ProcessDataBinding.java
;
藍色部分為中間產物,包括
1.data-binding-info
文件夾,包含了layout的基本信息,導入的變量,View標簽中的表達式,標簽的位置索引等等,如下所示為data-binding-info/activity_detail3-layout.xml
:
false
false
....
2.setter_store.bin
,包含所有setter相關信息;
3.layoutinfo.bin
,包含所有layout相關信息;
4.br.bin
,包含所有BR相關信息;
以上bin文件都以Serializable方式序列化到磁盤上,需要的時候進行反序列化操作;
data-binding-layout-out
(最終輸出到res/layout),即去掉根節點
,去掉節點
,與不使用Data Binding時的layout相一致,例如data-binding-layout-out/activity_detail2.xml
:
...
2.DataBindingInfo.class
,一個看似空的類,但在SOURCE階段包含了一個@BindingBuildInfo
注解,包含了基本DataBinding的基本信息,代碼如下:
// DataBindingInfo.class
public class DataBindingInfo {
public DataBindingInfo() {
}
}
// @BindingBuildInfo
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.SOURCE)
public @interface BindingBuildInfo {
String buildId();
String modulePackage();
String sdkRoot();
int minSdk();
String layoutInfoDir();
String exportClassListTo();
boolean isLibrary();
boolean enableDebugLogs() default false;
boolean printEncodedError() default false;
}
3.DataBindingComponent.class
,會根據自定義的DataBindingComponent自動生成對應實例化方法,例如:
public interface DataBindingComponent {
MyComponent getMyComponent();
}
4.ViewDataBinding.class
的子類(ActivityDetail2Binding.class等)
5.BR.class
,Bindable屬性索引表,例如:
public class BR {
public static final int _all = 0;
public static final int adapter = 1;
public static final int name = 2;
public static final int visibility = 3;
public BR() {
}
}
6.DataBindingMapper.class
,Mapper,用於尋找某個layout.xml對應的ViewDataBinding類,例如:
class DataBinderMapper {
static final int TARGET_MIN_SDK = 16;
public DataBinderMapper() {
}
public ViewDataBinding getDataBinder(DataBindingComponent bindingComponent, View view, int layoutId) {
switch(layoutId) {
case 2130968602:
return ActivityDetail2Binding.bind(view, bindingComponent);
case 2130968603:
return ActivityDetail3Binding.bind(view, bindingComponent);
....
default:
return null;
}
}
ViewDataBinding getDataBinder(DataBindingComponent bindingComponent, View[] views, int layoutId) {
return null;
}
int getLayoutId(String tag) {
if(tag == null) {
return 0;
} else {
int code = tag.hashCode();
switch(code) {
case -600937657:
if(tag.equals("layout/activity_detail2_0")) {
return 2130968602;
}
break;
case -600936696:
if(tag.equals("layout/activity_detail3_0")) {
return 2130968603;
}
break;
....
return 0;
}
}
String convertBrIdToString(int id) {
return id >= 0 && id < DataBinderMapper.InnerBrLookup.sKeys.length?DataBinderMapper.InnerBrLookup.sKeys[id]:null;
}
private static class InnerBrLookup {
static String[] sKeys = new String[]{"_all", "adapter", "name", "visibility"};
private InnerBrLookup() {
}
}
}
的data-binding-layout-out
以及DataBinding所需要的data-binding-info
; STEP2 DataBindingInfo.class生成DataBindingInfo.class
生成操作,把相關的信息寫入DataBindingInfo.class
的@BindingBuildInfo
注解中; STEP3 監聽到注解變化@BindingBuildInfo
注解,或者code中發現有新的注解寫入,AbstractProcessor注解處理器就開始執行注解處理。DataBinding中有一個ProcessDataBinding.java
類專門來處理DataBinding相關的注解; STEP4 ProcessDataBinding處理注解,生成binProcessMethodAdapter
,ProcessExpressions
,ProcessBindable
。每次執行都會從磁盤反序列化對應的bin文件,然後忘bin中寫入新的,完成後再序列化到磁盤; STEP5 生成最終產物ProcessMethodAdapter
生成DataBindingComponents.class
;執行ProcessExpressions
生成ViewDataBinding.class子類(ActivityDetail2Binding.class
),並觸發DataBindingMapper.class
更新;執行ProcessBindable
生成BR.class
,並觸發DataBindingMapper.class
更新;
第二章有講到View是如何注入的,其實需要分兩種情況:
* 1.如果這個View標簽屬性中只有id,沒有其他”@{表達式}”形式,則按照第2章提到的方式直接通過id查找;
* 2.如果這個View標簽屬性中有”@{表達式}”形式的值,則編譯器會自動給這個View加個android:tag=”binding_{N}”, 其中{N}按順序從0開始遞增,如android:tag=”binding_0”。當執行ViewDataBinding#mapBindings
去注入View時,會找tag為binding_開頭的View,隨後執行View注入;
另外,如果View標簽原來就有android:tag值,則編譯器會先保存原有值信息,寫入android:tag=”binding_{N}”。當執行完view注入後,再把原來的值賦值給android:tag。注意如果原來的android:tag值為”binding_0”,那麼在View注入時將會發生錯亂。
在完成View注入後,ActivityDetail3Binding會執行this.setRootTag(root)
,代碼如下:
public class ActivityDetail3Binding extends ViewDataBinding {
public ActivityDetail3Binding(DataBindingComponent bindingComponent, View root) {
super(bindingComponent, root, 0);
Object[] bindings = mapBindings(bindingComponent, root, 5, sIncludes, sViewsWithIds);
this.detailActionButton = (Button)bindings[4];
this.detailActionButton.setTag((Object)null);
...
this.setRootTag(root);
this.invalidateAll();
}
}
這與ListView中的ViewHoloder實現方式相似,所以如果把DataBinding運用到ListView的ViewHolder中,就不需要多生成一個ViewHolder,直接使用這個ViewDataBinding類即可,例如ListAdapter
實現:
public static class ListAdapter extends BaseAdapter{
...
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ItemFooBinding binding;
if (convertView == null){
LayoutInflater inflater = LayoutInflater.from(parent.getContext());
binding = DataBindingUtil.inflate(inflater,R.layout.item_foo,parent,false);
} else {
binding = DataBindingUtil.getBinding(convertView);
}
if (binding == null) return null;
bind(binding,position);
return binding.getRoot();
}
private void bind(ItemFooBinding binding, int position) {
binding.title.setText("position:" + position);
Context context = binding.avatar.getContext();
int colorId = position % 2 == 0 ? R.color.colorAccent : R.color.colorPrimary;
binding.avatar.setBackgroundColor(ContextCompat.getColor(context,colorId));
}
}
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