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();

}

}</pre><br>

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