Android Framework中的PolicyManager簡介

fmms 12年前發布 | 32K 次閱讀 Android Android開發 移動開發

PolicyManager 類位于framework\base\core\java\com\android\internal\policy目錄中的 PolicyManager.java文件中。PolicyManager主要用于創建Window類、LayoutInflater類和 WindowManagerPolicy類，它扮演著簡單工廠模式中的工廠類角色，而抽象產品角色由IPolicy接口實現，具體產品角色由Policy 類實現。它們的關系如下圖所示：

Android Framework中的PolicyManager簡介

從下面三個類的代碼可以看出，都使用了hide注解，因此，這三個類都是不對外公開的API，只限于Framework內部使用。

抽象產品類IPolicy實現如下（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();
}
具體產品類Policy實現如下（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類創建時預先加載的一些類
    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 {
        // 出于性能考慮，在Policy類加載時提前加載會用到的相關類
        for (String s : preload_classes) {
            try {
    //加載指定類到Java虛擬機中，并執行類中的靜態代碼段
                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();
    }
}
工廠類PolicyManager實現如下（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 {
        // 運行時動態裝載IPolicy實現類
        try {
            //加載Policy類的同時會執行其中的靜態代碼段
            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);
        }
    }

    // 構造函數私有，保證是單例類
    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();
    }
}
轉自：http://blog.csdn.net/ace1985/article/details/7253188

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