1# Developing a File Manager Application (for System Applications Only)
2
3OpenHarmony is prebuilt with the **FileManager** application. You can also develop your own file manager application as required.
4
5## How to Develop
6For details about the APIs used to develop a file manager, see [User File Access and Management](../reference/apis-core-file-kit/js-apis-fileAccess-sys.md).
7
81. Apply for permissions required.<br>Apply for the ohos.permission.FILE_ACCESS_MANAGER and ohos.permission.GET_BUNDLE_INFO_PRIVILEGED permissions. For details, see [Requesting Permissions for System_basic Applications](../security/AccessToken/determine-application-mode.md#requesting-permissions-for-system_basic-applications).
9
10> **NOTE**
11   >
12   > - The ohos.permission.FILE_ACCESS_MANAGER permission allows your application to use the user file access framework APIs.
13   >
14   > - The ohos.permission.GET_BUNDLE_INFO_PRIVILEGED permission allows your application to obtain information about file management server applications supported by the system.
15
162. Import dependent modules.
17
18   ```ts
19   import { fileAccess } from '@kit.CoreFileKit';
20   import { fileExtensionInfo } from '@kit.CoreFileKit';
21   ```
22
23   The **fileAccess** module provides APIs for basic file operations, and the **fileExtensionInfo** module provides key structs for application development.
24
253. Query device information.<br>
26   You can obtain attributes of the devices managed by one or all file management servers in the system. You can also filter devices as required.
27
28   In the user file access framework, **RootInfo** indicates the attribute information of a device. For example, obtain **RootInfo** of all devices.
29
30   ```ts
31   import { common } from '@kit.AbilityKit';
32   import { BusinessError } from '@kit.BasicServicesKit';
33   import { Filter } from '@kit.CoreFileKit';
34
35   // Obtain the application context.
36   let context = getContext(this) as common.UIAbilityContext;
37
38   // Create a helper object for connecting to all file management servers in the system.
39   let fileAccessHelperAllServer: fileAccess.FileAccessHelper;
40   function createFileAccessHelper(): void {
41     try {    // this.context is the context passed from EntryAbility.
42       fileAccessHelperAllServer = fileAccess.createFileAccessHelper(context);
43       if (!fileAccessHelperAllServer) {
44         console.error("createFileAccessHelper interface returns an undefined object");
45       }
46     } catch (err) {
47         let error: BusinessError = err as BusinessError;
48         console.error("createFileAccessHelper failed, errCode:" + error.code + ", errMessage:" + error.message);
49     }
50   }
51   let rootInfos: Array<fileAccess.RootInfo> = [];
52   async function getRoots(): Promise<void>{
53     let rootIterator: fileAccess.RootIterator;
54     let isDone: boolean = false;
55     try {
56       rootIterator = await fileAccessHelperAllServer.getRoots();
57       if (!rootIterator) {
58         console.error("getRoots interface returns an undefined object");
59         return;
60       }
61       while (!isDone) {
62         let result = rootIterator.next();
63         console.info("next result = " + JSON.stringify(result));
64         isDone = result.done;
65         if (!isDone)
66           rootInfos.push(result.value);
67       }
68     } catch (err) {
69       let error: BusinessError = err as BusinessError;
70       console.error("getRoots failed, errCode:" + error.code + ", errMessage:" + error.message);
71     }
72   }
73   ```
74
754. View directories.<br>
76   In the user file access framework, **FileInfo** indicates basic information about a file or folder. You can use **listfile()** to obtain a **FileIterator** object that traverses all files (folders) of the next level or use **scanfile()** to obtain a **FileIterator** object that meets the specified conditions.
77
78   Currently, **listfile()** and **scanfile()** can be called by the **RootInfo** object to traverse the next-level files or filter the entire directory tree. In addition, **listfile()** and **scanfile()** can be called by the **FileInfo** object to traverse the next-level files or filter the specified directories.
79
80   ```ts
81   import { BusinessError } from '@kit.BasicServicesKit';
82   import { Filter } from '@kit.CoreFileKit';
83
84   // Start from the root directory.
85   let rootInfos = [];
86   // Obtain rootInfos by using getRoots().
87   let rootInfo: fileAccess.RootInfo = rootInfos[0];
88   let fileInfos: Array<fileAccess.FileInfo> = [];
89   let isDone: boolean = false;
90   let filter: Filter = {suffix : [".txt", ".jpg", ".xlsx"]}; // Set the filter.
91   try {
92     let fileIterator = rootInfo.listFile();          // Traverse the root directory of rootinfos[0] and return a FileIterator object.
93     // let fileIterator = rootInfo.scanFile(filter); // Filter device rootinfos[0] files that meet the specified conditions and return a FileIterator object.
94     if (!fileIterator) {
95       console.error("listFile interface returns an undefined object");
96     }
97     while (!isDone) {
98       let result = fileIterator.next();
99       console.info("next result = " + JSON.stringify(result));
100       isDone = result.done;
101       if (!isDone)
102         fileInfos.push(result.value);
103     }
104   } catch (err) {
105    let error: BusinessError = err as BusinessError;
106     console.error("listFile failed, errCode:" + error.code + ", errMessage:" + error.message);
107   }
108
109   // Start from the specified directory.
110   let fileInfoDir: fileAccess.FileInfo = fileInfos[0]; // fileInfoDir indicates the information about a directory.
111   let subFileInfos: Array<fileAccess.FileInfo> = [];
112   let isDone02: boolean = false;
113   let filter02: Filter = {suffix : [".txt", ".jpg", ".xlsx"]}; // Set the filter.
114   try {
115     let fileIterator = fileInfoDir.listFile(); // Traverse files in the specified directory and return a FileIterator object.
116     // let fileIterator = rootInfo.scanFile(filter02); // Filter the files in the specified directory and return a FileIterator object.
117     if (!fileIterator) {
118       console.error("listFile interface returns an undefined object");
119     }
120     while (!isDone02) {
121       let result = fileIterator.next();
122       console.info("next result = " + JSON.stringify(result));
123       isDone02 = result.done;
124       if (!isDone02)
125         subFileInfos.push(result.value);
126     }
127   } catch (err) {
128    let error: BusinessError = err as BusinessError;
129     console.error("listFile failed, errCode:" + error.code + ", errMessage:" + error.message);
130   }
131   ```
132
1335. Perform operations on files or folders.<br>
134   You can integrate APIs of the user file access framework to implement user behaviors, such as deleting, renaming, creating, and moving a file or folder. The following example shows how to create a file. For details about other APIs, see [User File Access and Management](../reference/apis-core-file-kit/js-apis-fileAccess-sys.md).
135
136   ```ts
137   import { BusinessError } from '@kit.BasicServicesKit';
138
139   // The local device is used as an example.
140   // Create a file.
141   // sourceUri is the URI in fileinfo of the Download directory.
142   // You need to use the obtained URI for development.
143   async function creatFile(): Promise<void> {
144     let sourceUri: string = "file://docs/storage/Users/currentUser/Download";
145     let displayName: string = "file1";
146     let fileUri: string = '';
147     try {
148       // Obtain fileAccessHelperAllServer by referring to the sample code of fileAccess.createFileAccessHelper.
149       fileUri = await fileAccessHelperAllServer.createFile(sourceUri, displayName);
150       if (!fileUri) {
151         console.error("createFile return undefined object");
152       }
153       console.info("createFile success, fileUri: " + JSON.stringify(fileUri));
154     } catch (err) {
155      let error: BusinessError = err as BusinessError;
156      console.error("createFile failed, errCode:" + error.code + ", errMessage:" + error.message);
157     };
158   }
159   ```
160
161## Listening for Device Online/Offline Status
162
163For details about the APIs, see [User File Access and Management](../reference/apis-core-file-kit/js-apis-fileAccess-sys.md).
164
165You can use **notify()** to observe not only the changes of directories, but also the device online/offline status.
166
167
1681. Apply for permissions required.<br>
169
170   Apply for the ohos.permission.FILE_ACCESS_MANAGER and ohos.permission.GET_BUNDLE_INFO_PRIVILEGED permissions. For details, see [Declaring Permissions](../security/AccessToken/declare-permissions.md).
171
172   > **NOTE**
173   >
174   > - The ohos.permission.FILE_ACCESS_MANAGER permission allows your application to call the user file access framework APIs.
175   >- The ohos.permission.GET_BUNDLE_INFO_PRIVILEGED permission allows your application to obtain information about file management server applications supported by the system.
176
1772. Import dependent modules.
178
179   ```ts
180   import { fileAccess } from '@kit.CoreFileKit';
181   import { fileExtensionInfo } from '@kit.CoreFileKit';
182   ```
183
184   The **fileAccess** module provides APIs for basic file operations, and the **fileExtensionInfo** module provides key structs for application development.
185
1863. Define an observer callback.
187
188   ```ts
189   const callbackDir1 = (NotifyMessageDir: fileAccess.NotifyMessage) => {
190     if (NotifyMessageDir != undefined) {
191       console.log('NotifyType: ' + NotifyMessageDir.type + 'NotifyUri:' + NotifyMessageDir.uri[0]);
192     } else {
193      console.error("NotifyMessageDir is undefined");
194     }
195   }
196   ```
197
1984. Subscribe to the device online/offline status.
199
200     Pass in the constant [DEVICES_URI](../reference/apis-core-file-kit/js-apis-fileAccess-sys.md#constant) to the **registerObserver** method to listen for the device online/offline status.
201
202      ```ts
203      import { BusinessError } from '@kit.BasicServicesKit';
204      async function UnregisterObserver03() {
205        try {
206          // Listen for the device online/offline status.
207          fileAccessHelper.registerObserver(fileAccess.DEVICES_URI, true, callbackDir1);
208        } catch (err) {
209          let error: BusinessError = err as BusinessError;
210          console.error("unregisterObserver failed, errCode:" + error.code + ", errMessage:" + error.message);
211        }
212      }
213      ```
214
2155. Unsubscribe from the device online/offline status.
216
217   Pass in the constant [DEVICES_URI](../reference/apis-core-file-kit/js-apis-fileAccess-sys.md#constant) to the **unregisterObserver** method to unsubscribe from the device online/offline status.
218
219      ```ts
220      import { BusinessError } from '@kit.BasicServicesKit';
221        try {
222          // Unsubscribe from the device online/offline status.
223          fileAccessHelper.unregisterObserver(fileAccess.DEVICES_URI, callbackDir1);
224        } catch (err) {
225          let error: BusinessError = err as BusinessError;
226          console.error("unregisterObserver failed, errCode:" + error.code + ", errMessage:" + error.message);
227        }
228      ```