Android 中的注解深入探究

更新時(shí)間：2016年08月26日 15:53:09 作者：技術(shù)小黑屋

本文主要介紹 Android 注解這里提供了詳細(xì)的資料及示例代碼，有需要的小伙伴可以參考下

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注解是我們經(jīng)常接觸的技術(shù),Java有注解,Android也有注解,本文將試圖介紹Android中的注解,以及ButterKnife和Otto這些基于注解的庫的一些工作原理.

歸納而言,Android中的注解大概有以下好處

提高我們的開發(fā)效率
更早的發(fā)現(xiàn)程序的問題或者錯(cuò)誤
更好的增加代碼的描述能力
更加利于我們的一些規(guī)范約束
提供解決問題的更優(yōu)解

準(zhǔn)備工作

默認(rèn)情況下,Android中的注解包并沒有包括在framework中,它獨(dú)立成一個(gè)單獨(dú)的包,通常我們需要引入這個(gè)包.

dependencies {
  compile 'com.android.support:support-annotations:22.2.0'
}

但是如果我們已經(jīng)引入了appcompat則沒有必要再次引用support-annotations,因?yàn)閍ppcompat默認(rèn)包含了對其引用.

替代枚舉

在最早的時(shí)候,當(dāng)我們想要做一些值得限定實(shí)現(xiàn)枚舉的效果,通常是

定義幾個(gè)常量用于限定
從上面的常量選取值進(jìn)行使用
一個(gè)比較描述上面問題的示例代碼如下

public static final int COLOR_RED = 0;
public static final int COLOR_GREEN = 1;
public static final int COLOR_YELLOW = 2;

public void setColor(int color) {
  //some code here
}
//調(diào)用
setColor(COLOR_RED)

然而上面的還是有不盡完美的地方

setColor(COLOR_RED)與setColor(0)效果一樣,而后者可讀性很差,但卻可以正常運(yùn)行

setColor方法可以接受枚舉之外的值,比如setColor(3),這種情況下程序可能出問題

一個(gè)相對較優(yōu)的解決方法就是使用Java中的Enum.使用枚舉實(shí)現(xiàn)的效果如下

// ColorEnum.java
public enum ColorEmun {
  RED,
  GREEN,
  YELLOW
}

public void setColorEnum(ColorEmun colorEnum) {
  //some code here
}

setColorEnum(ColorEmun.GREEN);

然而Enum也并非最佳,Enum因?yàn)槠湎啾确桨敢坏某Ａ縼碚f,占用內(nèi)存相對大很多而受到曾經(jīng)被Google列為不建議使用,為此Google特意引入了一些相關(guān)的注解來替代枚舉.

Android中新引入的替代枚舉的注解有IntDef和StringDef,這里以IntDef做例子說明一下.

public class Colors {
  @IntDef({RED, GREEN, YELLOW})
  @Retention(RetentionPolicy.SOURCE)
  public @interface LightColors{}

  public static final int RED = 0;
  public static final int GREEN = 1;
  public static final int YELLOW = 2;
}

聲明必要的int常量
聲明一個(gè)注解為LightColors
使用@IntDef修飾LightColors,參數(shù)設(shè)置為待枚舉的集合
使用@Retention(RetentionPolicy.SOURCE)指定注解僅存在與源碼中,不加入到class文件中

Null相關(guān)的注解

和Null相關(guān)的注解有兩個(gè)

@Nullable 注解的元素可以是Null
@NonNull 注解的元素不能是Null

上面的兩個(gè)可以修飾如下的元素

成員屬性
方法參數(shù)
方法的返回值

@Nullable
private String obtainReferrerFromIntent(@NonNull Intent intent) {
  return intent.getStringExtra("apps_referrer");
}

NonNull檢測生效的條件

顯式傳入null
在調(diào)用方法之前已經(jīng)判斷了參數(shù)為null時(shí)

setReferrer(null);//提示警告

//不提示警告
String referrer = getIntent().getStringExtra("apps_referrer");
setReferrer(referrer);

//提示警告
String referrer = getIntent().getStringExtra("apps_referrer");
if (referrer == null) {
  setReferrer(referrer);
}

private void setReferrer(@NonNull String referrer) {
  //some code here
}

區(qū)間范圍注解

Android中的IntRange和FloatRange是兩個(gè)用來限定區(qū)間范圍的注解,

float currentProgress;

public void setCurrentProgress(@FloatRange(from=0.0f, to=1.0f) float progress) {
  currentProgress = progress;
}

如果我們傳入非法的值,如下所示

setCurrentProgress(11);

就會(huì)得到這樣的錯(cuò)誤

Value must be >=0.0 and <= 1.0(was 11)

長度以及數(shù)組大小限制

限制字符串的長度

private void setKey(@Size(6) String key) {
}

限定數(shù)組集合的大小

private void setData(@Size(max = 1) String[] data) {
}
setData(new String[]{"b", "a"});//error occurs

限定特殊的數(shù)組長度,比如3的倍數(shù)

private void setItemData(@Size(multiple = 3) String[] data) {
}

權(quán)限相關(guān)

在Android中,有很多場景都需要使用權(quán)限,無論是Marshmallow之前還是之后的動(dòng)態(tài)權(quán)限管理.都需要在manifest中進(jìn)行聲明,如果忘記了,則會(huì)導(dǎo)致程序崩潰. 好在有一個(gè)注解能輔助我們避免這個(gè)問題.使用RequiresPermission注解即可.

@RequiresPermission(Manifest.permission.SET_WALLPAPER)
  public void changeWallpaper(Bitmap bitmap) throws IOException {
}

資源注解

在Android中幾乎所有的資源都可以有對應(yīng)的資源id.比如獲取定義的字符串,我們可以通過下面的方法

public String getStringById(int stringResId) {
  return getResources().getString(stringResId);
}

使用這個(gè)方法,我們可以很容易的獲取到定義的字符串,但是這樣的寫法也存在著風(fēng)險(xiǎn).

getStringById(R.mipmap.ic_launcher)

如果我們在不知情或者疏忽情況下,傳入這樣的值,就會(huì)出現(xiàn)問題. 但是如果我們使用資源相關(guān)的注解修飾了參數(shù),就能很大程度上避免錯(cuò)誤的情況.

public String getStringById(@StringRes int stringResId) {
  return getResources().getString(stringResId);
}

在Android中資源注解如下所示

AnimRes
AnimatorRes
AnyRes
ArrayRes
AttrRes
BoolRes
ColorRes
DimenRes
DrawableRes
FractionRes
IdRes
IntegerRes
InterpolatorRes
LayoutRes
MenuRes
PluralsRes
RawRes
StringRes
StyleRes
StyleableRes
TransitionRes
XmlRes

Color值限定

上面部分提到了ColorRes,用來限定顏色資源id,這里我們將使用ColorInt,一個(gè)用來限定Color值的注解. 在較早的TextView的setTextColor是這樣實(shí)現(xiàn)的.

public void setTextColor(int color) {
  mTextColor = ColorStateList.valueOf(color);
  updateTextColors();
}

然而上面的方法在調(diào)用時(shí)常常會(huì)出現(xiàn)這種情況

myTextView.setTextColor(R.color.colorAccent);

如上,如果傳遞過去的參數(shù)為color的資源id就會(huì)出現(xiàn)顏色取錯(cuò)誤的問題,這個(gè)問題在過去還是比較嚴(yán)重的.好在ColorInt出現(xiàn)了,改變了這一問題.

public void setTextColor(@ColorInt int color) {
  mTextColor = ColorStateList.valueOf(color);
  updateTextColors();
}

當(dāng)我們再次傳入Color資源值時(shí),就會(huì)得到錯(cuò)誤的提示.

CheckResult

這是一個(gè)關(guān)于返回結(jié)果的注解，用來注解方法，如果一個(gè)方法得到了結(jié)果，卻沒有使用這個(gè)結(jié)果，就會(huì)有錯(cuò)誤出現(xiàn)，一旦出現(xiàn)這種錯(cuò)誤，就說明你沒有正確使用該方法。

@CheckResult
public String trim(String s) {
  return s.trim();
}

線程相關(guān)

Android中提供了四個(gè)與線程相關(guān)的注解

@UiThread,通?？梢缘韧谥骶€程,標(biāo)注方法需要在UIThread執(zhí)行,比如View類就使用這個(gè)注解
@MainThread 主線程,經(jīng)常啟動(dòng)后創(chuàng)建的第一個(gè)線程
@WorkerThread 工作者線程,一般為一些后臺的線程,比如AsyncTask里面的doInBackground就是這樣的.
@BinderThread 注解方法必須要在BinderThread線程中執(zhí)行,一般使用較少.

一些示例

new AsyncTask<Void, Void, Void>() {
    //doInBackground is already annotated with @WorkerThread
    @Override
    protected Void doInBackground(Void... params) {
      return null;
      updateViews();//error
    }
  };

@UiThread
public void updateViews() {
  Log.i(LOGTAG, "updateViews ThreadInfo=" + Thread.currentThread());
}

注意,這種情況下不會(huì)出現(xiàn)錯(cuò)誤提示

new Thread(){
  @Override
  public void run() {
    super.run();
    updateViews();
  }
}.start();

雖然updateViews會(huì)在一個(gè)新的工作者線程中執(zhí)行,但是在compile時(shí)沒有錯(cuò)誤提示.

因?yàn)樗呐袛嘁罁?jù)是,如果updateView的線程注解(這里為@UiThread)和run(沒有線程注解)不一致才會(huì)錯(cuò)誤提示.如果run方法沒有線程注解,則不提示.

CallSuper

重寫的方法必須要調(diào)用super方法

使用這個(gè)注解,我們可以強(qiáng)制方法在重寫時(shí)必須調(diào)用父類的方法比如Application的onCreate,onConfigurationChanged等.

Keep

在Android編譯生成APK的環(huán)節(jié),我們通常需要設(shè)置minifyEnabled為true實(shí)現(xiàn)下面的兩個(gè)效果

混淆代碼

刪除沒有用的代碼

但是出于某一些目的,我們需要不混淆某部分代碼或者不刪除某處代碼,除了配置復(fù)雜的Proguard文件之外,我們還可以使用@Keep注解 .

@Keep
public static int getBitmapWidth(Bitmap bitmap) {
  return bitmap.getWidth();
}

ButterKnife

ButterKnife是一個(gè)用來綁定View,資源和回調(diào)的提高效率的工具.作者為Jake Wharton. ButterKnife的好處

使用BindView替代繁瑣的findViewById和類型轉(zhuǎn)換
使用OnClick注解方法來替換顯式聲明的匿名內(nèi)部類
使用BindString,BindBool,BindDrawable等注解實(shí)現(xiàn)資源獲取

一個(gè)摘自Github的示例

class ExampleActivity extends Activity {
 @BindView(R.id.user) EditText username;
 @BindView(R.id.pass) EditText password;

 @BindString(R.string.login_error) String loginErrorMessage;

 @OnClick(R.id.submit) void submit() {
  // TODO call server...
 }

 @Override public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.simple_activity);
  ButterKnife.bind(this);
  // TODO Use fields...
 }
}

ButterKnife工作原理

以BindView注解使用為例,示例代碼為

public class MainActivity extends AppCompatActivity {
  @BindView(R.id.myTextView)
  TextView myTextView;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ButterKnife.bind(this);
  }
}

1.程序在compile時(shí),會(huì)根據(jù)注解自動(dòng)生成兩個(gè)類,這里為MainActivity_ViewBinder.class和MainActivity_ViewBinding.class

2.當(dāng)我們調(diào)用ButterKnife.bind(this);時(shí),會(huì)查找當(dāng)前類對應(yīng)的ViewBinder類,并調(diào)用bind方法,這里會(huì)調(diào)用到MainActiivty_ViewBinder.bind方法.

3.MainActiivty_ViewBinder.bind方法實(shí)際上是調(diào)用了findViewById然后在進(jìn)行類型轉(zhuǎn)換,賦值給MainActivity的myTextView屬性

ButterKnife的bind方法

public static Unbinder bind(@NonNull Activity target) {
  return getViewBinder(target).bind(Finder.ACTIVITY, target, target);
}

ButterKnife的getViewBinder和findViewBinderForClass

@NonNull @CheckResult @UiThread
 static ViewBinder<Object> getViewBinder(@NonNull Object target) {
  Class<?> targetClass = target.getClass();
  if (debug) Log.d(TAG, "Looking up view binder for " + targetClass.getName());
  return findViewBinderForClass(targetClass);
 }

 @NonNull @CheckResult @UiThread
 private static ViewBinder<Object> findViewBinderForClass(Class<?> cls) {
  //如果內(nèi)存集合BINDERS中包含,則不再查找
  ViewBinder<Object> viewBinder = BINDERS.get(cls);
  if (viewBinder != null) {
   if (debug) Log.d(TAG, "HIT: Cached in view binder map.");
   return viewBinder;
  }
  String clsName = cls.getName();
  if (clsName.startsWith("android.") || clsName.startsWith("java.")) {
   if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search.");
   return NOP_VIEW_BINDER;
  }
  //noinspection TryWithIdenticalCatches Resolves to API 19+ only type.
  try {
   //使用反射創(chuàng)建實(shí)例
   Class<?> viewBindingClass = Class.forName(clsName + "_ViewBinder");
   //noinspection unchecked
   viewBinder = (ViewBinder<Object>) viewBindingClass.newInstance();
   if (debug) Log.d(TAG, "HIT: Loaded view binder class.");
  } catch (ClassNotFoundException e) {
    //如果沒有找到,對父類進(jìn)行查找
   if (debug) Log.d(TAG, "Not found. Trying superclass " + cls.getSuperclass().getName());
   viewBinder = findViewBinderForClass(cls.getSuperclass());
  } catch (InstantiationException e) {
   throw new RuntimeException("Unable to create view binder for " + clsName, e);
  } catch (IllegalAccessException e) {
   throw new RuntimeException("Unable to create view binder for " + clsName, e);
  }
  //加入內(nèi)存集合,便于后續(xù)的查找
  BINDERS.put(cls, viewBinder);
  return viewBinder;
 }

MainActivity_ViewBinder的反編譯源碼

➜ androidannotationsample javap -c MainActivity_ViewBinder
Warning: Binary file MainActivity_ViewBinder contains com.example.admin.androidannotationsample.MainActivity_ViewBinder
Compiled from "MainActivity_ViewBinder.java"
public final class com.example.admin.androidannotationsample.MainActivity_ViewBinder implements butterknife.internal.ViewBinder<com.example.admin.androidannotationsample.MainActivity> {
 public com.example.admin.androidannotationsample.MainActivity_ViewBinder();
  Code:
    0: aload_0
    1: invokespecial #1         // Method java/lang/Object."<init>":()V
    4: return

 public butterknife.Unbinder bind(butterknife.internal.Finder, com.example.admin.androidannotationsample.MainActivity, java.lang.Object);
  Code:
    0: new      #2         // class com/example/admin/androidannotationsample/MainActivity_ViewBinding
    3: dup
    4: aload_2
    5: aload_1
    6: aload_3              // 創(chuàng)建ViewBinding實(shí)例
    7: invokespecial #3         // Method com/example/admin/androidannotationsample/MainActivity_ViewBinding."<init>":(Lcom/example/admin/androidannotationsample/MainActivity;Lbutterknife/internal/Finder;Ljava/lang/Object;)V
   10: areturn

 public butterknife.Unbinder bind(butterknife.internal.Finder, java.lang.Object, java.lang.Object);
  Code:
    0: aload_0
    1: aload_1
    2: aload_2
    3: checkcast   #4         // class com/example/admin/androidannotationsample/MainActivity
    6: aload_3              //調(diào)用上面的重載方法
    7: invokevirtual #5         // Method bind:(Lbutterknife/internal/Finder;Lcom/example/admin/androidannotationsample/MainActivity;Ljava/lang/Object;)Lbutterknife/Unbinder;
   10: areturn
}
MainActivity_ViewBinding的反編譯源碼

➜ androidannotationsample javap -c MainActivity_ViewBinding
Warning: Binary file MainActivity_ViewBinding contains com.example.admin.androidannotationsample.MainActivity_ViewBinding
Compiled from "MainActivity_ViewBinding.java"
public class com.example.admin.androidannotationsample.MainActivity_ViewBinding<T extends com.example.admin.androidannotationsample.MainActivity> implements butterknife.Unbinder {
 protected T target;

 public com.example.admin.androidannotationsample.MainActivity_ViewBinding(T, butterknife.internal.Finder, java.lang.Object);
  Code:
    0: aload_0
    1: invokespecial #1         // Method java/lang/Object."<init>":()V
    4: aload_0
    5: aload_1
    6: putfield   #2         // Field target:Lcom/example/admin/androidannotationsample/MainActivity;
    9: aload_1
   10: aload_2
   11: aload_3              //調(diào)用Finder.findRequireViewAsType找到View,并進(jìn)行類型轉(zhuǎn)換,并復(fù)制給MainActivity中對一個(gè)的變量
   12: ldc      #4         // int 2131427412
   14: ldc      #5         // String field 'myTextView'
   16: ldc      #6         // class android/widget/TextView
                      // 內(nèi)部實(shí)際調(diào)用了findViewById
   18: invokevirtual #7         // Method butterknife/internal/Finder.findRequiredViewAsType:(Ljava/lang/Object;ILjava/lang/String;Ljava/lang/Class;)Ljava/lang/Object;
   21: checkcast   #6         // class android/widget/TextView
   24: putfield   #8         // Field com/example/admin/androidannotationsample/MainActivity.myTextView:Landroid/widget/TextView;
   27: return

 public void unbind();
  Code:
    0: aload_0
    1: getfield   #2         // Field target:Lcom/example/admin/androidannotationsample/MainActivity;
    4: astore_1
    5: aload_1
    6: ifnonnull   19
    9: new      #9         // class java/lang/IllegalStateException
   12: dup
   13: ldc      #10         // String Bindings already cleared.
   15: invokespecial #11         // Method java/lang/IllegalStateException."<init>":(Ljava/lang/String;)V
   18: athrow
   19: aload_1
   20: aconst_null            // 解除綁定,設(shè)置對應(yīng)的變量為null
   21: putfield   #8         // Field com/example/admin/androidannotationsample/MainActivity.myTextView:Landroid/widget/TextView;
   24: aload_0
   25: aconst_null
   26: putfield   #2         // Field target:Lcom/example/admin/androidannotationsample/MainActivity;
   29: return
}

Finder的源碼

package butterknife.internal;

import android.app.Activity;
import android.app.Dialog;
import android.content.Context;
import android.support.annotation.IdRes;
import android.view.View;

@SuppressWarnings("UnusedDeclaration") // Used by generated code.
public enum Finder {
 VIEW {
  @Override public View findOptionalView(Object source, @IdRes int id) {
   return ((View) source).findViewById(id);
  }

  @Override public Context getContext(Object source) {
   return ((View) source).getContext();
  }

  @Override protected String getResourceEntryName(Object source, @IdRes int id) {
   final View view = (View) source;
   // In edit mode, getResourceEntryName() is unsupported due to use of BridgeResources
   if (view.isInEditMode()) {
    return "<unavailable while editing>";
   }
   return super.getResourceEntryName(source, id);
  }
 },
 ACTIVITY {
  @Override public View findOptionalView(Object source, @IdRes int id) {
   return ((Activity) source).findViewById(id);
  }

  @Override public Context getContext(Object source) {
   return (Activity) source;
  }
 },
 DIALOG {
  @Override public View findOptionalView(Object source, @IdRes int id) {
   return ((Dialog) source).findViewById(id);
  }

  @Override public Context getContext(Object source) {
   return ((Dialog) source).getContext();
  }
 };

 //查找對應(yīng)的Finder,如上面的ACTIVITY, DIALOG, VIEW
 public abstract View findOptionalView(Object source, @IdRes int id);

 public final <T> T findOptionalViewAsType(Object source, @IdRes int id, String who,
   Class<T> cls) {
  View view = findOptionalView(source, id);
  return castView(view, id, who, cls);
 }

 public final View findRequiredView(Object source, @IdRes int id, String who) {
  View view = findOptionalView(source, id);
  if (view != null) {
   return view;
  }
  String name = getResourceEntryName(source, id);
  throw new IllegalStateException("Required view '"
    + name
    + "' with ID "
    + id
    + " for "
    + who
    + " was not found. If this view is optional add '@Nullable' (fields) or '@Optional'"
    + " (methods) annotation.");
 }

 //來自ViewBinding的調(diào)用
 public final <T> T findRequiredViewAsType(Object source, @IdRes int id, String who,
   Class<T> cls) {
  View view = findRequiredView(source, id, who);
  return castView(view, id, who, cls);
 }

 public final <T> T castView(View view, @IdRes int id, String who, Class<T> cls) {
  try {
   return cls.cast(view);
  } catch (ClassCastException e) {
   String name = getResourceEntryName(view, id);
   throw new IllegalStateException("View '"
     + name
     + "' with ID "
     + id
     + " for "
     + who
     + " was of the wrong type. See cause for more info.", e);
  }
 }

 @SuppressWarnings("unchecked") // That's the point.
 public final <T> T castParam(Object value, String from, int fromPos, String to, int toPos) {
  try {
   return (T) value;
  } catch (ClassCastException e) {
   throw new IllegalStateException("Parameter #"
     + (fromPos + 1)
     + " of method '"
     + from
     + "' was of the wrong type for parameter #"
     + (toPos + 1)
     + " of method '"
     + to
     + "'. See cause for more info.", e);
  }
 }

 protected String getResourceEntryName(Object source, @IdRes int id) {
  return getContext(source).getResources().getResourceEntryName(id);
 }

 public abstract Context getContext(Object source);
}

Otto

Otto Bus 是一個(gè)專為Android改裝的Event Bus,在很多項(xiàng)目中都有應(yīng)用.由Square開源共享.

public class EventBusTest {
  private static final String LOGTAG = "EventBusTest";
  Bus mBus = new Bus();

  public void test() {
    mBus.register(this);
  }

  class NetworkChangedEvent {

  }

  @Produce
  public NetworkChangedEvent sendNetworkChangedEvent() {
    return new NetworkChangedEvent();
  }

  @Subscribe
  public void onNetworkChanged(NetworkChangedEvent event) {
    Log.i(LOGTAG, "onNetworkChanged event=" + event);
  }
}

Otto 的工作原理

使用@Produce和@Subscribe標(biāo)記方法
當(dāng)調(diào)用bus.register方法,去檢索注冊對象的標(biāo)記方法,并cache映射關(guān)系
當(dāng)post事件時(shí),將事件與handler方法對應(yīng)加入事件隊(duì)列
抽取事件隊(duì)列,然后調(diào)用handler處理

如下為對Otto如何利用注解的分析

register的源碼

public void register(Object object) {
  if (object == null) {
   throw new NullPointerException("Object to register must not be null.");
  }
  enforcer.enforce(this);
  //查找object中的Subscriber
  Map<Class<?>, Set<EventHandler>> foundHandlersMap = handlerFinder.findAllSubscribers(object);
  for (Class<?> type : foundHandlersMap.keySet()) {
   Set<EventHandler> handlers = handlersByType.get(type);
   if (handlers == null) {
    //concurrent put if absent
    Set<EventHandler> handlersCreation = new CopyOnWriteArraySet<EventHandler>();
    handlers = handlersByType.putIfAbsent(type, handlersCreation);
    if (handlers == null) {
      handlers = handlersCreation;
    }
   }
   final Set<EventHandler> foundHandlers = foundHandlersMap.get(type);
   if (!handlers.addAll(foundHandlers)) {
    throw new IllegalArgumentException("Object already registered.");
   }
  }

  for (Map.Entry<Class<?>, Set<EventHandler>> entry : foundHandlersMap.entrySet()) {
   Class<?> type = entry.getKey();
   EventProducer producer = producersByType.get(type);
   if (producer != null && producer.isValid()) {
    Set<EventHandler> foundHandlers = entry.getValue();
    for (EventHandler foundHandler : foundHandlers) {
     if (!producer.isValid()) {
      break;
     }
     if (foundHandler.isValid()) {
      dispatchProducerResultToHandler(foundHandler, producer);
     }
    }
   }
  }
 }

HandlerFinder源碼

interface HandlerFinder {

 Map<Class<?>, EventProducer> findAllProducers(Object listener);

 Map<Class<?>, Set<EventHandler>> findAllSubscribers(Object listener);

 //Otto注解查找器
 HandlerFinder ANNOTATED = new HandlerFinder() {
  @Override
  public Map<Class<?>, EventProducer> findAllProducers(Object listener) {
   return AnnotatedHandlerFinder.findAllProducers(listener);
  }

  @Override
  public Map<Class<?>, Set<EventHandler>> findAllSubscribers(Object listener) {
   return AnnotatedHandlerFinder.findAllSubscribers(listener);
  }
 };

具體查找實(shí)現(xiàn)

/** This implementation finds all methods marked with a {@link Subscribe} annotation. */
 static Map<Class<?>, Set<EventHandler>> findAllSubscribers(Object listener) {
  Class<?> listenerClass = listener.getClass();
  Map<Class<?>, Set<EventHandler>> handlersInMethod = new HashMap<Class<?>, Set<EventHandler>>();

  Map<Class<?>, Set<Method>> methods = SUBSCRIBERS_CACHE.get(listenerClass);
  if (null == methods) {
   methods = new HashMap<Class<?>, Set<Method>>();
   loadAnnotatedSubscriberMethods(listenerClass, methods);
  }
  if (!methods.isEmpty()) {
   for (Map.Entry<Class<?>, Set<Method>> e : methods.entrySet()) {
    Set<EventHandler> handlers = new HashSet<EventHandler>();
    for (Method m : e.getValue()) {
     handlers.add(new EventHandler(listener, m));
    }
    handlersInMethod.put(e.getKey(), handlers);
   }
  }

  return handlersInMethod;
 }

以上就是關(guān)于Android中注解的一些總結(jié),文章部分內(nèi)容參考自 Support Annotations ,希望能幫助大家對注解有基礎(chǔ)的認(rèn)識,并運(yùn)用到實(shí)際的日常開發(fā)之中。

通過此文希望能幫助你徹底了解Android 注解機(jī)制,謝謝大家對本站的支持！

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