Android Framework中的PolicyManager简介
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):
[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):
[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):
[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();
- }
- }
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