Android Framework中的PolicyManager簡介

PolicyManager類位於framework\base\core\java\com\Android\internal\policy目錄中的PolicyManager.java文件中。PolicyManager主要用於創建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：

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，只限於Framework內部使用。

抽象產品類IPolicy實現如下（IPolicy.java）：

1. package com.android.internal.policy;
3. import android.content.Context;
4. import android.view.LayoutInflater;
5. import android.view.Window;
6. import android.view.WindowManagerPolicy;
8. /**
9. * {@hide}
10. */
12. /* The implementation of this interface must be called Policy and contained
13. * within the com.android.internal.policy.impl package */
14. public interface IPolicy {
15. public Window makeNewWindow(Context context);
17. public LayoutInflater makeNewLayoutInflater(Context context);
19. public WindowManagerPolicy makeNewWindowManager();
20. }

具體產品類Policy實現如下（Policy.java）：

1. package com.android.internal.policy.impl;
3. import android.content.Context;
4. import android.util.Log;
6. import com.android.internal.policy.IPolicy;
7. import com.android.internal.policy.impl.PhoneLayoutInflater;
8. import com.android.internal.policy.impl.PhoneWindow;
9. import com.android.internal.policy.impl.PhoneWindowManager;
11. /**
12. * {@hide}
13. */
15. // Simple implementation of the policy interface that spawns the right
16. // set of objects
17. public class Policy implements IPolicy {
18. private static final String TAG = "PhonePolicy";
20. //需要在Policy類創建時預先加載的一些類
21. private static final String[] preload_classes = {
22. "com.android.internal.policy.impl.PhoneLayoutInflater",
23. "com.android.internal.policy.impl.PhoneWindow",
24. "com.android.internal.policy.impl.PhoneWindow$1",
25. "com.android.internal.policy.impl.PhoneWindow$ContextMenuCallback",
26. "com.android.internal.policy.impl.PhoneWindow$DecorView",
27. "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState",
28. "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState$SavedState",
29. };
31. static {
32. // 出於性能考慮，在Policy類加載時提前加載會用到的相關類
33. for (String s : preload_classes) {
34. try {
35. //加載指定類到Java虛擬機中，並執行類中的靜態代碼段
36. Class.forName(s);
37. } catch (ClassNotFoundException ex) {
38. Log.e(TAG, "Could not preload class for phone policy: " + s);
39. }
40. }
41. }
43. public PhoneWindow makeNewWindow(Context context) {
44. return new PhoneWindow(context);
45. }
47. public PhoneLayoutInflater makeNewLayoutInflater(Context context) {
48. return new PhoneLayoutInflater(context);
49. }
51. //PhoneWindowManager實現了WindowManagerPolicy接口
52. //這裡返回值直接寫成WindowManagerPolicy更合理些
53. public PhoneWindowManager makeNewWindowManager() {
54. return new PhoneWindowManager();
55. }
56. }

工廠類PolicyManager實現如下（PolicyManager.java）：

1. package com.android.internal.policy;
3. import android.content.Context;
4. import android.view.LayoutInflater;
5. import android.view.Window;
6. import android.view.WindowManagerPolicy;
8. import com.android.internal.policy.IPolicy;
10. /**
11. * {@hide}
12. */
14. public final class PolicyManager {
15. private static final String POLICY_IMPL_CLASS_NAME =
16. "com.android.internal.policy.impl.Policy";
18. private static final IPolicy sPolicy;
20. static {
21. // 運行時動態裝載IPolicy實現類
22. try {
23. //加載Policy類的同時會執行其中的靜態代碼段
24. Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
25. sPolicy = (IPolicy)policyClass.newInstance();
26. } catch (ClassNotFoundException ex) {
27. throw new RuntimeException(
28. POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
29. } catch (InstantiationException ex) {
30. throw new RuntimeException(
31. POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
32. } catch (IllegalAccessException ex) {
33. throw new RuntimeException(
34. POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
35. }
36. }
38. // 構造函數私有，保證是單例類
39. private PolicyManager() {}
41. // The static methods to spawn new policy-specific objects
42. public static Window makeNewWindow(Context context) {
43. return sPolicy.makeNewWindow(context);
44. }
46. public static LayoutInflater makeNewLayoutInflater(Context context) {
47. return sPolicy.makeNewLayoutInflater(context);
48. }
50. public static WindowManagerPolicy makeNewWindowManager() {
51. return sPolicy.makeNewWindowManager();
52. }
53. }