1# Subscribing to Crash Events (C/C++)
2
3## Available APIs
4
5For details about how to use the APIs (such as parameter usage restrictions and value ranges), see [HiAppEvent](../reference/apis-performance-analysis-kit/_hi_app_event.md#hiappevent).
6
7**Subscription APIs**
8
9| API                                                      | Description                                        |
10| ------------------------------------------------------------ | -------------------------------------------- |
11| int OH_HiAppEvent_AddWatcher(HiAppEvent_Watcher \*watcher)   | Adds a watcher to listen for application events.|
12| int OH_HiAppEvent_RemoveWatcher (HiAppEvent_Watcher \*watcher) | Removes a watcher to unsubscribe from application events.|
13
14## How to Develop
15
16The following describes how to subscribe to the crash event triggered by a button click.
17
181. Create a native C++ project and import the **jsoncpp** file to the project. The directory structure is as follows:
19
20   ```yml
21   entry:
22     src:
23       main:
24         cpp:
25           - json:
26               - json.h
27               - json-forwards.h
28           - types:
29               libentry:
30                 - index.d.ts
31           - CMakeLists.txt
32           - napi_init.cpp
33           - jsoncpp.cpp
34         ets:
35           - entryability:
36               - EntryAbility.ets
37           - pages:
38               - Index.ets
39   ```
40
412. In the **CMakeLists.txt** file, add the source file and dynamic libraries.
42
43   ```cmake
44   # Add the jsoncpp.cpp file, which is used to parse the JSON strings in the subscription events.
45   add_library(entry SHARED napi_init.cpp jsoncpp.cpp)
46   # Add libhiappevent_ndk.z.so and libhilog_ndk.z.so (log output). 
47   target_link_libraries(entry PUBLIC libace_napi.z.so libhilog_ndk.z.so libhiappevent_ndk.z.so)
48   ```
49
503. Import the dependency files to the **napi_init.cpp** file, and define **LOG_TAG**.
51
52   ```c++
53   # include "json/json.h"
54   # include "hilog/log.h"
55   # include "hiappevent/hiappevent.h"
56   
57   # undef LOG_TAG
58   # define LOG_TAG "testTag"
59   ```
60
614. Subscribe to application events.
62
63   - Watcher of the onReceive type:
64
65     In the **napi_init.cpp** file, define the methods related to the watcher of the onReceive type.
66
67     ```c++
68     // Define a variable to cache the pointer to the created watcher.
69     static HiAppEvent_Watcher *systemEventWatcher; 
70     
71     static void OnReceive(const char *domain, const struct HiAppEvent_AppEventGroup *appEventGroups, uint32_t groupLen) {
72         for (int i = 0; i < groupLen; ++i) {
73             for (int j = 0; j < appEventGroups[i].infoLen; ++j) {
74                 OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.domain=%{public}s", appEventGroups[i].appEventInfos[j].domain);
75                 OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.name=%{public}s", appEventGroups[i].appEventInfos[j].name);
76                 OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.eventType=%{public}d", appEventGroups[i].appEventInfos[j].type);
77                 if (strcmp(appEventGroups[i].appEventInfos[j].domain, DOMAIN_OS) == 0 && 
78                     strcmp(appEventGroups[i].appEventInfos[j].name, EVENT_APP_CRASH) == 0) {
79                     Json::Value params;
80                     Json::Reader reader(Json::Features::strictMode());
81                     Json::FastWriter writer;
82                     if (reader.parse(appEventGroups[i].appEventInfos[j].params, params)) {
83                         auto time = params["time"].asInt64();
84                         auto crashType = params["crash_type"].asString();
85                         auto foreground = params["foreground"].asBool();
86                         auto bundleVersion = params["bundle_version"].asString();
87                         auto bundleName = params["bundle_name"].asString();
88                         auto pid = params["pid"].asInt();
89                         auto uid = params["uid"].asInt();
90                         auto uuid = params["uuid"].asString();
91                         auto exception = writer.write(params["exception"]);
92                         auto hilogSize = params["hilog"].size();
93                         auto externalLog = writer.write(params["external_log"]);
94                         auto logOverLimit = params["log_over_limit"].asBool();
95                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.time=%{public}lld", time);
96                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.crash_type=%{public}s", crashType.c_str());
97                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.foreground=%{public}d", foreground);
98                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.bundle_version=%{public}s", bundleVersion.c_str());
99                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.bundle_name=%{public}s", bundleName.c_str());
100                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.pid=%{public}d", pid);
101                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.uid=%{public}d", uid);
102                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.uuid=%{public}s", uuid.c_str());
103                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.exception=%{public}s", exception.c_str());
104                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.hilog.size=%{public}d", hilogSize);
105                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.external_log=%{public}s", externalLog.c_str());
106                         OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.log_over_limit=%{public}d", logOverLimit);
107                     }
108                 }
109             }
110         }
111     }
112     
113     static napi_value RegisterWatcher(napi_env env, napi_callback_info info) {
114         // Set the watcher name. The system identifies different watchers based on their names.
115         systemEventWatcher = OH_HiAppEvent_CreateWatcher("onReceiverWatcher");
116         // Set the event type to EVENT_APP_CRASH.
117         const char *names[] = {EVENT_APP_CRASH};
118         // Add the system events to watch, for example, system events.
119         OH_HiAppEvent_SetAppEventFilter(systemEventWatcher, DOMAIN_OS, 0, names, 1);
120         // Set the implemented callback. After receiving the event, the watcher immediately triggers the OnReceive callback.
121         OH_HiAppEvent_SetWatcherOnReceive(systemEventWatcher, OnReceive);
122         // Add a watcher to listen for the specified event.
123         OH_HiAppEvent_AddWatcher(systemEventWatcher);
124         return {};
125     }
126     ```
127     
128   - Watcher of the onTrigger type:
129
130     In the **napi_init.cpp** file, define the methods related to the watcher of the OnTrigger type.
131
132     ```c++
133     // Define a variable to cache the pointer to the created watcher.
134     static HiAppEvent_Watcher *systemEventWatcher;
135     
136     // Implement the callback function used to return the listened events. The content pointed to by the events pointer is valid only in this function.
137     static void OnTake(const char *const *events, uint32_t eventLen) {
138         Json::Reader reader(Json::Features::strictMode());
139         Json::FastWriter writer;
140         for (int i = 0; i < eventLen; ++i) {
141             Json::Value eventInfo;
142             if (reader.parse(events[i], eventInfo)) {
143                 auto domain =  eventInfo["domain_"].asString();
144                 auto name = eventInfo["name_"].asString();
145                 auto type = eventInfo["type_"].asInt();
146                 OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.domain=%{public}s", domain.c_str());
147                 OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.name=%{public}s", name.c_str());
148                 OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.eventType=%{public}d", type);
149                 if (domain ==  DOMAIN_OS && name == EVENT_APP_CRASH) {
150                     auto time = eventInfo["time"].asInt64();
151                     auto crashType = eventInfo["crash_type"].asString();
152                     auto foreground = eventInfo["foreground"].asBool();
153                     auto bundleVersion = eventInfo["bundle_version"].asString();
154                     auto bundleName = eventInfo["bundle_name"].asString();
155                     auto pid = eventInfo["pid"].asInt();
156                     auto uid = eventInfo["uid"].asInt();
157                     auto uuid = eventInfo["uuid"].asString();
158                     auto exception = writer.write(eventInfo["exception"]);
159                     auto hilogSize = eventInfo["hilog"].size();
160                     auto externalLog = writer.write(eventInfo["external_log"]);
161                     auto logOverLimit = eventInfo["log_over_limit"].asBool();
162                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.time=%{public}lld", time);
163                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.crash_type=%{public}s", crashType.c_str());
164                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.foreground=%{public}d", foreground);
165                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.bundle_version=%{public}s", bundleVersion.c_str());
166                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.bundle_name=%{public}s", bundleName.c_str());
167                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.pid=%{public}d", pid);
168                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.uid=%{public}d", uid);
169                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.uuid=%{public}s", uuid.c_str());
170                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.exception=%{public}s", exception.c_str());
171                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.hilog.size=%{public}d", hilogSize);
172                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.external_log=%{public}s", externalLog.c_str());
173                     OH_LOG_INFO(LogType::LOG_APP, "HiAppEvent eventInfo.params.log_over_limit=%{public}d", logOverLimit);
174                 }
175             }
176         }
177     }
178     
179     // Implement the subscription callback function to apply custom processing to the obtained event logging data.
180     static void OnTrigger(int row, int size) {
181         // After the callback is received, obtain the specified number of received events.
182         OH_HiAppEvent_TakeWatcherData(systemEventWatcher, row, OnTake);
183     }
184     
185     static napi_value RegisterWatcher(napi_env env, napi_callback_info info) {
186         // Set the watcher name. The system identifies different watchers based on their names.
187         systemEventWatcher = OH_HiAppEvent_CreateWatcher("onTriggerWatcher");
188         // Set the event type to EVENT_APP_CRASH.
189         const char *names[] = {EVENT_APP_CRASH};
190         // Add the system events to watch, for example, system events.
191         OH_HiAppEvent_SetAppEventFilter(systemEventWatcher, DOMAIN_OS, 0, names, 1);
192         // Set the implemented callback function. The callback function will be triggered when the conditions set by OH_HiAppEvent_SetTriggerCondition are met.
193         OH_HiAppEvent_SetWatcherOnTrigger(systemEventWatcher, OnTrigger);
194         // Set the conditions for triggering the subscription callback. For example, trigger this onTrigger callback when the number of new event logs is 1.
195         OH_HiAppEvent_SetTriggerCondition(systemEventWatcher, 1, 0, 0);
196         // Add a watcher to listen for the specified event.
197         OH_HiAppEvent_AddWatcher(systemEventWatcher);
198         return {};
199     }
200     ```
201
2025. Register **RegisterWatcher** as an ArkTS API.
203
204   In the **napi_init.cpp** file, register **RegisterWatcher** as an ArkTS API.
205
206   ```c++
207   static napi_value Init(napi_env env, napi_value exports)
208   {
209       napi_property_descriptor desc[] = {
210           { "registerWatcher", nullptr, RegisterWatcher, nullptr, nullptr, nullptr, napi_default, nullptr }
211       };
212       napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc);
213       return exports;
214   }
215   ```
216
217   In the **index.d.ts** file, define ArkTS APIs.
218
219   ```typescript
220   export const registerWatcher: () => void;
221   ```
222
2236. In the **EntryAbility.ets** file, add the following interface to **onCreate()**.
224
225   ```typescript
226   // Import the dependent module.
227   import testNapi from 'libentry.so'
228
229   // Add the interface to onCreate().
230   // Register the system event watcher at startup.
231   testNapi.registerWatcher();
232   ```
233
2347. In the **Index.ets** file, add a button to trigger the crash event.
235
236   ```typescript
237   Button("appCrash").onClick(() => {
238     JSON.parse("");
239   })
240   ```
241
2428. In DevEco Studio, click the **Run** button to run the project. Then, click the **appCrash** button to trigger a crash event. 
243
2449. The application crashes. After restarting the application, you can view the following event information in the **Log** window.
245
246   ```text
247   HiAppEvent eventInfo.domain=OS
248   HiAppEvent eventInfo.name=APP_CRASH
249   HiAppEvent eventInfo.eventType=1
250   HiAppEvent eventInfo.params.time=1502032265088
251   HiAppEvent eventInfo.params.crash_type=JsError
252   HiAppEvent eventInfo.params.foreground=1
253   HiAppEvent eventInfo.params.bundle_version=1.0.0
254   HiAppEvent eventInfo.params.bundle_name=com.example.myapplication
255   HiAppEvent eventInfo.params.pid=19237
256   HiAppEvent eventInfo.params.uid=20010043
257   HiAppEvent eventInfo.params.uuid=cc0f062e1b28c1fd2c817fafab5e8ca3207925b4bdd87c43ed23c60029659e01
258   HiAppEvent eventInfo.params.exception={"message":"Unexpected Text in JSON","name":"SyntaxError","stack":"at anonymous (entry/src/main/ets/pages/Index.ets:16:11)"}
259   HiAppEvent eventInfo.params.hilog.size=110
260   HiAppEvent eventInfo.params.external_log=["/data/storage/el2/log/hiappevent/APP_CRASH_1502032265211_19237.log"]
261   HiAppEvent eventInfo.params.log_over_limit=0
262   ```
263
26410. Remove the application event watcher.
265
266    ```c++
267    static napi_value RemoveWatcher(napi_env env, napi_callback_info info) {
268        // Remove the watcher.
269        OH_HiAppEvent_RemoveWatcher(systemEventWatcher);
270        return {};
271    }
272    ```
273
27411. Destroy the application event watcher.
275
276    ```c++
277    static napi_value DestroyWatcher(napi_env env, napi_callback_info info) {
278        // Destroy the created watcher and set systemEventWatcher to nullptr.
279        OH_HiAppEvent_DestroyWatcher(systemEventWatcher);
280        systemEventWatcher = nullptr;
281        return {};
282    }
283    ```
284
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