Android Framework中的PolicyManager简介

本文主要是介绍Android Framework中的PolicyManager简介，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

PolicyManager类位于framework\base\core\java\com\android\internal\policy目录中的PolicyManager.java文件中。PolicyManager主要用于创建Window类、LayoutInflater类和WindowManagerPolicy类，它扮演着简单工厂模式中的工厂类角色，而抽象产品角色由IPolicy接口实现，具体产品角色由Policy类实现。它们的关系如下图所示：

 

 

从下面三个类的代码可以看出，都使用了hide注解，因此，这三个类都是不对外公开的API，只限于Framework内部使用。

抽象产品类IPolicy实现如下（IPolicy.java）：

[java]
 package com.android.internal.policy;
 
 import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.Window;
 import android.view.WindowManagerPolicy;
 
 /**
  * {@hide}
  */
 
 /* The implementation of this interface must be called Policy and contained
  * within the com.android.internal.policy.impl package */
 public interface IPolicy {
     public Window makeNewWindow(Context context);
 
     public LayoutInflater makeNewLayoutInflater(Context context);
 
     public WindowManagerPolicy makeNewWindowManager();
 }
 package com.android.internal.policy;
 
import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.Window;
 import android.view.WindowManagerPolicy;
 
/**
  * {@hide}
  */
 
/* The implementation of this interface must be called Policy and contained
  * within the com.android.internal.policy.impl package */
 public interface IPolicy {
     public Window makeNewWindow(Context context);
 
    public LayoutInflater makeNewLayoutInflater(Context context);
 
    public WindowManagerPolicy makeNewWindowManager();
 }
 
 具体产品类Policy实现如下（Policy.java）：
 
[java]
 package com.android.internal.policy.impl;
 
 import android.content.Context;
 import android.util.Log;
 
 import com.android.internal.policy.IPolicy;
 import com.android.internal.policy.impl.PhoneLayoutInflater;
 import com.android.internal.policy.impl.PhoneWindow;
 import com.android.internal.policy.impl.PhoneWindowManager;
 
 /**
  * {@hide}
  */
 
 // Simple implementation of the policy interface that spawns the right 
 // set of objects 
 public class Policy implements IPolicy {
     private static final String TAG = "PhonePolicy";
 
     //需要在Policy类创建时预先加载的一些类 
     private static final String[] preload_classes = {
         "com.android.internal.policy.impl.PhoneLayoutInflater",
         "com.android.internal.policy.impl.PhoneWindow",
         "com.android.internal.policy.impl.PhoneWindow$1",
         "com.android.internal.policy.impl.PhoneWindow$ContextMenuCallback",
         "com.android.internal.policy.impl.PhoneWindow$DecorView",
         "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState",
  "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState$SavedState",
     };
 
     static {
         // 出于性能考虑，在Policy类加载时提前加载会用到的相关类 
         for (String s : preload_classes) {
             try {
         //加载指定类到Java虚拟机中，并执行类中的静态代码段 
                 Class.forName(s);
             } catch (ClassNotFoundException ex) {
                 Log.e(TAG, "Could not preload class for phone policy: " + s);
             }
         }
     }
 
     public PhoneWindow makeNewWindow(Context context) {
         return new PhoneWindow(context);
     }
 
     public PhoneLayoutInflater makeNewLayoutInflater(Context context) {
         return new PhoneLayoutInflater(context);
     }
 
     //PhoneWindowManager实现了WindowManagerPolicy接口     
     //这里返回值直接写成WindowManagerPolicy更合理些 
     public PhoneWindowManager makeNewWindowManager() {
         return new PhoneWindowManager();
     }
 }
 package com.android.internal.policy.impl;
 
import android.content.Context;
 import android.util.Log;
 
import com.android.internal.policy.IPolicy;
 import com.android.internal.policy.impl.PhoneLayoutInflater;
 import com.android.internal.policy.impl.PhoneWindow;
 import com.android.internal.policy.impl.PhoneWindowManager;
 
/**
  * {@hide}
  */
 
// Simple implementation of the policy interface that spawns the right
 // set of objects
 public class Policy implements IPolicy {
     private static final String TAG = "PhonePolicy";
 
    //需要在Policy类创建时预先加载的一些类
     private static final String[] preload_classes = {
         "com.android.internal.policy.impl.PhoneLayoutInflater",
         "com.android.internal.policy.impl.PhoneWindow",
         "com.android.internal.policy.impl.PhoneWindow$1",
         "com.android.internal.policy.impl.PhoneWindow$ContextMenuCallback",
         "com.android.internal.policy.impl.PhoneWindow$DecorView",
         "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState",
  "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState$SavedState",
     };
 
    static {
         // 出于性能考虑，在Policy类加载时提前加载会用到的相关类
         for (String s : preload_classes) {
             try {
      //加载指定类到Java虚拟机中，并执行类中的静态代码段
                 Class.forName(s);
             } catch (ClassNotFoundException ex) {
                 Log.e(TAG, "Could not preload class for phone policy: " + s);
             }
         }
     }
 
    public PhoneWindow makeNewWindow(Context context) {
         return new PhoneWindow(context);
     }
 
    public PhoneLayoutInflater makeNewLayoutInflater(Context context) {
         return new PhoneLayoutInflater(context);
     }
 
    //PhoneWindowManager实现了WindowManagerPolicy接口  
     //这里返回值直接写成WindowManagerPolicy更合理些
     public PhoneWindowManager makeNewWindowManager() {
         return new PhoneWindowManager();
     }
 }
 
 工厂类PolicyManager实现如下（PolicyManager.java）：
 
[java]
 <pre class="java" name="code">package com.android.internal.policy;
 
 import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.Window;
 import android.view.WindowManagerPolicy;
 
 import com.android.internal.policy.IPolicy;
 
 /**
  * {@hide}
  */
 
 public final class PolicyManager {
     private static final String POLICY_IMPL_CLASS_NAME =
         "com.android.internal.policy.impl.Policy";
 
     private static final IPolicy sPolicy;
 
     static {
        // 运行时动态装载IPolicy实现类 
         try {
            //加载Policy类的同时会执行其中的静态代码段 
             Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
             sPolicy = (IPolicy)policyClass.newInstance();
         } catch (ClassNotFoundException ex) {
             throw new RuntimeException(
                     POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
         } catch (InstantiationException ex) {
             throw new RuntimeException(
                     POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
         } catch (IllegalAccessException ex) {
             throw new RuntimeException(
                     POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
         }
     }
 
     // 构造函数私有，保证是单例类 
     private PolicyManager() {}
 
     // The static methods to spawn new policy-specific objects 
     public static Window makeNewWindow(Context context) {
         return sPolicy.makeNewWindow(context);
     }
 
     public static LayoutInflater makeNewLayoutInflater(Context context) {
         return sPolicy.makeNewLayoutInflater(context);
     }
 
     public static WindowManagerPolicy makeNewWindowManager() {
         return sPolicy.makeNewWindowManager();
     }
 }
 <pre class="java" name="code">package com.android.internal.policy;
 
import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.Window;
 import android.view.WindowManagerPolicy;
 
import com.android.internal.policy.IPolicy;
 
/**
  * {@hide}
  */
 
public final class PolicyManager {
     private static final String POLICY_IMPL_CLASS_NAME =
         "com.android.internal.policy.impl.Policy";
 
    private static final IPolicy sPolicy;
 
    static {
        // 运行时动态装载IPolicy实现类
         try {
            //加载Policy类的同时会执行其中的静态代码段
             Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
             sPolicy = (IPolicy)policyClass.newInstance();
         } catch (ClassNotFoundException ex) {
             throw new RuntimeException(
                     POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
         } catch (InstantiationException ex) {
             throw new RuntimeException(
                     POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
         } catch (IllegalAccessException ex) {
             throw new RuntimeException(
                     POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
         }
     }
 
    // 构造函数私有，保证是单例类
     private PolicyManager() {}
 
    // The static methods to spawn new policy-specific objects
     public static Window makeNewWindow(Context context) {
         return sPolicy.makeNewWindow(context);
     }
 
    public static LayoutInflater makeNewLayoutInflater(Context context) {
         return sPolicy.makeNewLayoutInflater(context);
     }
 
    public static WindowManagerPolicy makeNewWindowManager() {
         return sPolicy.makeNewWindowManager();
     }
 }
 

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