Android Framework中的PolicyManager简介

fmms 13年前

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：

Android Framework中的PolicyManager简介

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）：

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）：
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);      }        public PhoneWindowManager makeNewWindowManager() {          return new PhoneWindowManager();      }  }
工厂类PolicyManager实现如下（PolicyManager.java）：
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();      }  }
转自：http://blog.csdn.net/ace1985/article/details/7253188