Android Framework中的PolicyManager简介

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）：

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); } //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）：

<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(); } }