Android应用如何监听自己是否被卸载及卸载反馈功能的实现（第三版）

两个月前发了两篇有关监听自己是否被卸载和卸载反馈功能实现的博客，第二版的地址如下：http://www.cnblogs.com/zealotrouge/p/3159772.html，感谢@whiletrue_童鞋发现了我的代码在4.2.2系统上无法实现卸载反馈，经过调试，有了问题的解决方案，但是由于发完博客后即处于闭关开发阶段，没时间打理博客，所以解决方案迟迟没有与大家见面，最近空闲下来，将解决思路及方案发出来给大家看看还有没有问题。

　　调试发现，监听依然没有问题，毕竟是Linux Kernel中的接口，Framework层再怎么改也改不到那儿去，那么问题出在哪呢？阻塞结束后，通过调用exec函数发出am命令调起浏览器访问网页，在API16（Android 4.1.x）的设备上尚可正常访问网页，而API17（Android 4.2.x）的设备上连浏览器也不能调起。

　　通过分析log，发现了一条线索，如下面的log的所示：

W/ActivityManager( 387): Permission Denial: startActivity asks to run as user -2 but is calling from user 0; this requires android.permission.INTERACT_ACROSS_USERS_FULL
　　log中直接给出提示，需要加一个权限INTERACT_ACROSS_USERS_FULL，这个权限时API17新引入的，目的在于允许不同用户的应用之间可以产生交互。可是加上去之后发现，还不是无法调起浏览器，而且log依然提示需要权限INTERACT_ACROSS_USERS_FULL，很是奇怪，于是继续分析。

　　首先说明一下Linux中的pid和uid，以及android扩展的userSerialNumber。pid是Process的标识，用于系统对进程的控制，从API层面看就是用于Process.killProcess()和Process.sendSignal()；uid在Linux系统中是用来标识用户的，而在android将uid视为app的标识id，用于"sandbox"安全模型，即用于app权限控制；而对于API17引入的多用户支持（目前只支持平板），uid已经被占用，只好新引入userSerialNumber来标识用户。

　　回到刚才的问题，log中告知startActivity时运行用户标识为-2，而调用却是由用户标识0发起，导致拒绝执行。用这句话搜索，发现在Google开发者网站中有相关的issue，链接如下：https://code.google.com/p/android/issues/detail?id=39801（打不开可以把https改为http）。结合官方的回答，问题原因如下：由于被卸载，C端进程监听到目录被删除，立即执行am命令，此时将会默认以USER_CURRENT的身份执行，由于API17中ActivityManagerService.handleIncomingUser()会校验userSerialNumber，发现用户标识不匹配，导致权限校验失败——这也说明了权限的影响范围仅限于Java端的进程，对于fork()出来的C端进程来说，并不继承父进程在Android中声明的权限。

　　解决方案：增加处理分支，若API>=17，将userSerialNumber传递给C端进程，然后在am命令中带上参数--user userSerialNumber即可。

Java端代码如下：



  1 package main.activity;
  2
  3 import java.lang.reflect.InvocationTargetException;
  4 import java.lang.reflect.Method;
  5
  6 import pym.test.uninstalledobserver.R;
  7 import android.app.Activity;
  8 import android.os.Build;
  9 import android.os.Bundle;
10 import android.util.Log;
11
12 /**
13  * @author pengyiming
14  * @note 监听此应用是否被卸载，若被卸载则弹出卸载反馈
15  * @note 由于API17加入多用户支持，原有命令在4.2及更高版本上执行时缺少userSerial参数，特此修改
16  *
17  */
18
19 public class UninstalledObserverActivity extends Activity
20 {
21     /* 数据段begin */
22     private static final String TAG = "UninstalledObserverActivity";
23    
24     // 监听进程pid
25     private int mObserverProcessPid = -1;
26     /* 数据段end */
27    
28     /* static */
29     // 初始化监听进程
30     private native int init(String userSerial);
31     static
32     {
33         Log.d(TAG, "load lib --> uninstalled_observer");
34         System.loadLibrary("uninstalled_observer");
35     }
36     /* static */
37    
38     /* 函数段begin */
39     @Override
40     public void onCreate(Bundle savedInstanceState)
41     {
42         super.onCreate(savedInstanceState);
43        
44         setContentView(R.layout.uninstalled_observer_layout);
45        
46         // API level小于17，不需要获取userSerialNumber
47         if (Build.VERSION.SDK_INT < 17)
48         {
49             mObserverProcessPid = init(null);
50         }
51         // 否则，需要获取userSerialNumber
52         else
53         {
54             mObserverProcessPid = init(getUserSerial());
55         }
56     }
57    
58     @Override
59     protected void onDestroy()
60     {
61         super.onDestroy();
62        
63         // 示例代码，用于结束监听进程
64 //        if (mObserverProcessPid > 0)
65 //        {
66 //            android.os.Process.killProcess(mObserverProcessPid);
67 //        }
68     }
69    
70     // 由于targetSdkVersion低于17，只能通过反射获取
71     private String getUserSerial()
72     {
73         Object userManager = getSystemService("user");
74         if (userManager == null)
75         {
76             Log.e(TAG, "userManager not exsit !!!");
77             return null;
78         }
79        
80         try
81         {
82             Method myUserHandleMethod = android.os.Process.class.getMethod("myUserHandle", (Class<?>[]) null);
83             Object myUserHandle = myUserHandleMethod.invoke(android.os.Process.class, (Object[]) null);
84            
85             Method getSerialNumberForUser = userManager.getClass().getMethod("getSerialNumberForUser", myUserHandle.getClass());
86             long userSerial = (Long) getSerialNumberForUser.invoke(userManager, myUserHandle);
87             return String.valueOf(userSerial);
88         }
89         catch (NoSuchMethodException e)
90         {
91             Log.e(TAG, "", e);
92         }
93         catch (IllegalArgumentException e)
94         {
95             Log.e(TAG, "", e);
96         }
97         catch (IllegalAccessException e)
98         {
99             Log.e(TAG, "", e);
100         }
101         catch (InvocationTargetException e)
102         {
103             Log.e(TAG, "", e);
104         }
105        
106         return null;
107     }
108     /* 函数段end */
109 }


核心——native方法头文件：



1 /* 头文件begin */
2 #include <jni.h>
3 #include <stdlib.h>
4 #include <stdio.h>
5 #include <string.h>
6 #include <unistd.h>
7 #include <fcntl.h>
8 #include <sys/inotify.h>
9 #include <sys/stat.h>
10
11 #include <android/log.h>
12 /* 头文件end */
13
14 /* 宏定义begin */
15 //清0宏
16 #define MEM_ZERO(pDest, destSize) memset(pDest, 0, destSize)
17
18 //LOG宏定义
19 #define LOG_INFO(tag, msg) __android_log_write(ANDROID_LOG_INFO, tag, msg)
20 #define LOG_DEBUG(tag, msg) __android_log_write(ANDROID_LOG_DEBUG, tag, msg)
21 #define LOG_WARN(tag, msg) __android_log_write(ANDROID_LOG_WARN, tag, msg)
22 #define LOG_ERROR(tag, msg) __android_log_write(ANDROID_LOG_ERROR, tag, msg)
23 /* 宏定义end */
24
25 #ifndef _Included_main_activity_UninstalledObserverActivity
26 #define _Included_main_activity_UninstalledObserverActivity
27 #ifdef __cplusplus
28 extern "C" {
29 #endif
30
31 #undef main_activity_UninstalledObserverActivity_MODE_PRIVATE
32 #define main_activity_UninstalledObserverActivity_MODE_PRIVATE 0L
33 #undef main_activity_UninstalledObserverActivity_MODE_WORLD_READABLE
34 #define main_activity_UninstalledObserverActivity_MODE_WORLD_READABLE 1L
35 #undef main_activity_UninstalledObserverActivity_MODE_WORLD_WRITEABLE
36 #define main_activity_UninstalledObserverActivity_MODE_WORLD_WRITEABLE 2L
37 #undef main_activity_UninstalledObserverActivity_MODE_APPEND
38 #define main_activity_UninstalledObserverActivity_MODE_APPEND 32768L
39 #undef main_activity_UninstalledObserverActivity_MODE_MULTI_PROCESS
40 #define main_activity_UninstalledObserverActivity_MODE_MULTI_PROCESS 4L
41 #undef main_activity_UninstalledObserverActivity_BIND_AUTO_CREATE
42 #define main_activity_UninstalledObserverActivity_BIND_AUTO_CREATE 1L
43 #undef main_activity_UninstalledObserverActivity_BIND_DEBUG_UNBIND
44 #define main_activity_UninstalledObserverActivity_BIND_DEBUG_UNBIND 2L
45 #undef main_activity_UninstalledObserverActivity_BIND_NOT_FOREGROUND
46 #define main_activity_UninstalledObserverActivity_BIND_NOT_FOREGROUND 4L
47 #undef main_activity_UninstalledObserverActivity_BIND_ABOVE_CLIENT
48 #define main_activity_UninstalledObserverActivity_BIND_ABOVE_CLIENT 8L
49 #undef main_activity_UninstalledObserverActivity_BIND_ALLOW_OOM_MANAGEMENT
50 #define main_activity_UninstalledObserverActivity_BIND_ALLOW_OOM_MANAGEMENT 16L
51 #undef main_activity_UninstalledObserverActivity_BIND_WAIVE_PRIORITY
52 #define main_activity_UninstalledObserverActivity_BIND_WAIVE_PRIORITY 32L
53 #undef main_activity_UninstalledObserverActivity_BIND_IMPORTANT
54 #define main_activity_UninstalledObserverActivity_BIND_IMPORTANT 64L
55 #undef main_activity_UninstalledObserverActivity_BIND_ADJUST_WITH_ACTIVITY
56 #define main_activity_UninstalledObserverActivity_BIND_ADJUST_WITH_ACTIVITY 128L
57 #undef main_activity_UninstalledObserverActivity_CONTEXT_INCLUDE_CODE
58 #define main_activity_UninstalledObserverActivity_CONTEXT_INCLUDE_CODE 1L
59 #undef main_activity_UninstalledObserverActivity_CONTEXT_IGNORE_SECURITY
60 #define main_activity_UninstalledObserverActivity_CONTEXT_IGNORE_SECURITY 2L
61 #undef main_activity_UninstalledObserverActivity_CONTEXT_RESTRICTED
62 #define main_activity_UninstalledObserverActivity_CONTEXT_RESTRICTED 4L
63 #undef main_activity_UninstalledObserverActivity_RESULT_CANCELED
64 #define main_activity_UninstalledObserverActivity_RESULT_CANCELED 0L
65 #undef main_activity_UninstalledObserverActivity_RESULT_OK
66 #define main_activity_UninstalledObserverActivity_RESULT_OK -1L
67 #undef main_activity_UninstalledObserverActivity_RESULT_FIRST_USER
68 #define main_activity_UninstalledObserverActivity_RESULT_FIRST_USER 1L
69 #undef main_activity_UninstalledObserverActivity_DEFAULT_KEYS_DISABLE
70 #define main_activity_UninstalledObserverActivity_DEFAULT_KEYS_DISABLE 0L
71 #undef main_activity_UninstalledObserverActivity_DEFAULT_KEYS_DIALER
72 #define main_activity_UninstalledObserverActivity_DEFAULT_KEYS_DIALER 1L
73 #undef main_activity_UninstalledObserverActivity_DEFAULT_KEYS_SHORTCUT
74 #define main_activity_UninstalledObserverActivity_DEFAULT_KEYS_SHORTCUT 2L
75 #undef main_activity_UninstalledObserverActivity_DEFAULT_KEYS_SEARCH_LOCAL
76 #define main_activity_UninstalledObserverActivity_DEFAULT_KEYS_SEARCH_LOCAL 3L
77 #undef main_activity_UninstalledObserverActivity_DEFAULT_KEYS_SEARCH_GLOBAL
78 #define main_activity_UninstalledObserverActivity_DEFAULT_KEYS_SEARCH_GLOBAL 4L
79
80 /*
81  * Class:     main_activity_UninstalledObserverActivity
82  * Method:    init
83  * Signature: (Ljava/lang/String;)V
84  */
85 JNIEXPORT int JNICALL Java_main_activity_UninstalledObserverActivity_init(JNIEnv *, jobject, jstring);
86
87 #ifdef __cplusplus
88 }
89 #endif
90 #endif


核心——native方法实现：



  1 /* 头文件begin */
  2 #include "main_activity_UninstalledObserverActivity.h"
  3 /* 头文件end */
  4
  5 #ifdef __cplusplus
  6 extern "C"
  7 {
  8 #endif
  9
10 /* 内全局变量begin */
11 static char TAG[] = "UninstalledObserverActivity.init";
12 static jboolean isCopy = JNI_TRUE;
13
14 static const char APP_DIR[] = "/data/data/pym.test.uninstalledobserver";
15 static const char APP_FILES_DIR[] = "/data/data/pym.test.uninstalledobserver/files";
16 static const char APP_OBSERVED_FILE[] = "/data/data/pym.test.uninstalledobserver/files/observedFile";
17 static const char APP_LOCK_FILE[] = "/data/data/pym.test.uninstalledobserver/files/lockFile";
18 /* 内全局变量 */
19
20 /*
21  * Class:     main_activity_UninstalledObserverActivity
22  * Method:    init
23  * Signature: ()V
24  * return: 子进程pid
25  */
26 JNIEXPORT int JNICALL Java_main_activity_UninstalledObserverActivity_init(JNIEnv *env, jobject obj, jstring userSerial)
27 {
28     jstring tag = (*env)->NewStringUTF(env, TAG);
29
30     LOG_DEBUG((*env)->GetStringUTFChars(env, tag, &isCopy)
31             , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "init observer"), &isCopy));
32
33     // fork子进程，以执行轮询任务
34     pid_t pid = fork();
35     if (pid < 0)
36     {
37         LOG_ERROR((*env)->GetStringUTFChars(env, tag, &isCopy)
38                 , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "fork failed !!!"), &isCopy));
39
40         exit(1);
41     }
42     else if (pid == 0)
43     {
44         // 若监听文件所在文件夹不存在，创建
45         FILE *p_filesDir = fopen(APP_FILES_DIR, "r");
46         if (p_filesDir == NULL)
47         {
48             int filesDirRet = mkdir(APP_FILES_DIR, S_IRWXU | S_IRWXG | S_IXOTH);
49             if (filesDirRet == -1)
50             {
51                 LOG_ERROR((*env)->GetStringUTFChars(env, tag, &isCopy)
52                         , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "mkdir failed !!!"), &isCopy));
53
54                 exit(1);
55             }
56         }
57
58         // 若被监听文件不存在，创建文件
59         FILE *p_observedFile = fopen(APP_OBSERVED_FILE, "r");
60         if (p_observedFile == NULL)
61         {
62             p_observedFile = fopen(APP_OBSERVED_FILE, "w");
63         }
64         fclose(p_observedFile);
65
66         // 创建锁文件，通过检测加锁状态来保证只有一个卸载监听进程
67         int lockFileDescriptor = open(APP_LOCK_FILE, O_RDONLY);
68         if (lockFileDescriptor == -1)
69         {
70             lockFileDescriptor = open(APP_LOCK_FILE, O_CREAT);
71         }
72         int lockRet = flock(lockFileDescriptor, LOCK_EX | LOCK_NB);
73         if (lockRet == -1)
74         {
75             LOG_DEBUG((*env)->GetStringUTFChars(env, tag, &isCopy)
76                     , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "observed by another process"), &isCopy));
77
78             exit(0);
79         }
80         LOG_DEBUG((*env)->GetStringUTFChars(env, tag, &isCopy)
81                     , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "observed by child process"), &isCopy));
82
83         // 分配空间，以便读取event
84         void *p_buf = malloc(sizeof(struct inotify_event));
85         if (p_buf == NULL)
86         {
87             LOG_ERROR((*env)->GetStringUTFChars(env, tag, &isCopy)
88                     , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "malloc failed !!!"), &isCopy));
89
90             exit(1);
91         }
92         // 分配空间，以便打印mask
93         int maskStrLength = 7 + 10 + 1;// mask=0x占7字节，32位整形数最大为10位，转换为字符串占10字节，'\0'占1字节
94         char *p_maskStr = malloc(maskStrLength);
95         if (p_maskStr == NULL)
96         {
97             free(p_buf);
98
99             LOG_ERROR((*env)->GetStringUTFChars(env, tag, &isCopy)
100                     , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "malloc failed !!!"), &isCopy));
101
102             exit(1);
103         }
104
105         // 开始监听
106         LOG_DEBUG((*env)->GetStringUTFChars(env, tag, &isCopy)
107                 , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "start observe"), &isCopy));
108
109         // 初始化
110         int fileDescriptor = inotify_init();
111         if (fileDescriptor < 0)
112         {
113             free(p_buf);
114             free(p_maskStr);
115
116             LOG_ERROR((*env)->GetStringUTFChars(env, tag, &isCopy)
117                     , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "inotify_init failed !!!"), &isCopy));
118
119             exit(1);
120         }
121
122         // 添加被监听文件到监听列表
123         int watchDescriptor = inotify_add_watch(fileDescriptor, APP_OBSERVED_FILE, IN_ALL_EVENTS);
124         if (watchDescriptor < 0)
125         {
126             free(p_buf);
127             free(p_maskStr);
128
129             LOG_ERROR((*env)->GetStringUTFChars(env, tag, &isCopy)
130                     , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "inotify_add_watch failed !!!"), &isCopy));
131
132             exit(1);
133         }
134
135         while(1)
136         {
137             // read会阻塞进程
138             size_t readBytes = read(fileDescriptor, p_buf, sizeof(struct inotify_event));
139
140             // 打印mask
141             snprintf(p_maskStr, maskStrLength, "mask=0x%x\0", ((struct inotify_event *) p_buf)->mask);
142             LOG_DEBUG((*env)->GetStringUTFChars(env, tag, &isCopy)
143                     , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, p_maskStr), &isCopy));
144
145             // 若文件被删除，可能是已卸载，还需进一步判断app文件夹是否存在
146             if (IN_DELETE_SELF == ((struct inotify_event *) p_buf)->mask)
147             {
148                 FILE *p_appDir = fopen(APP_DIR, "r");
149                 // 确认已卸载
150                 if (p_appDir == NULL)
151                 {
152                     inotify_rm_watch(fileDescriptor, watchDescriptor);
153
154                     break;
155                 }
156                 // 未卸载，可能用户执行了"清除数据"
157                 else
158                 {
159                     fclose(p_appDir);
160
161                     // 重新创建被监听文件，并重新监听
162                     FILE *p_observedFile = fopen(APP_OBSERVED_FILE, "w");
163                     fclose(p_observedFile);
164
165                     int watchDescriptor = inotify_add_watch(fileDescriptor, APP_OBSERVED_FILE, IN_ALL_EVENTS);
166                     if (watchDescriptor < 0)
167                     {
168                         free(p_buf);
169                         free(p_maskStr);
170
171                         LOG_ERROR((*env)->GetStringUTFChars(env, tag, &isCopy)
172                                 , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "inotify_add_watch failed !!!"), &isCopy));
173
174                         exit(1);
175                     }
176                 }
177             }
178         }
179
180         // 释放资源
181         free(p_buf);
182         free(p_maskStr);
183
184         // 停止监听
185         LOG_DEBUG((*env)->GetStringUTFChars(env, tag, &isCopy)
186                 , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "stop observe"), &isCopy));
187
188         if (userSerial == NULL)
189         {
190             // 执行命令am start -a android.intent.action.VIEW -d $(url)
191             execlp("am", "am", "start", "-a", "android.intent.action.VIEW", "-d", "http://www.baidu.com", (char *)NULL);
192         }
193         else
194         {
195             // 执行命令am start --user userSerial -a android.intent.action.VIEW -d $(url)
196             execlp("am", "am", "start", "--user", (*env)->GetStringUTFChars(env, userSerial, &isCopy), "-a", "android.intent.action.VIEW", "-d", "http://www.baidu.com", (char *)NULL);
197         }
198
199         // 执行命令失败log
200         LOG_ERROR((*env)->GetStringUTFChars(env, tag, &isCopy)
201                 , (*env)->GetStringUTFChars(env, (*env)->NewStringUTF(env, "exec AM command failed !!!"), &isCopy));
202     }
203     else
204     {
205         // 父进程直接退出，使子进程被init进程领养，以避免子进程僵死，同时返回子进程pid
206         return pid;
207     }
208 }
209
210 #ifdef __cplusplus
211 }
212 #endif




注一：此次代码修复了评论中提到的一些bug，比如清除数据、插拔USB线、覆盖安装等操作引起程序误判卸载。
注二：在同事指点下，针对任何情况导致重复监听的问题，都可以通过加文件锁来防止，这比ps并读取返回结果并过滤进程名的方法要好很多。

注三：安装在SD卡此卸载监听依然没有问题，但是如果用户将已在Internal SD卡安装好的应用移动到external SD卡，由于.c的161行未重新files文件夹和锁文件，应该会bug，代码都有，需要的自行修复此bug即可。