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1# @ohos.systemParameterEnhance (System Parameter)
2
3The **SystemParameter** module provides system services with easy access to key-value pairs. You can use the APIs provided by this module to describe the service status and change the service behavior. The basic operation primitives are get and set. You can obtain the values of system parameters through getters and modify the values through setters.
4For details about the system parameter design principles and definitions, see
5[Service Management](../../../device-dev/subsystems/subsys-boot-init-sysparam.md).
6
7> **NOTE**
8>
9> - The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version.
10> - The APIs provided by this module are system APIs.
11> - Third-party applications cannot use the APIs provided by this module, because system parameters each require specific discretionary access control (DAC) and mandatory access control (MAC) permissions.
12
13## Modules to Import
14
15```ts
16import systemparameter from '@ohos.systemParameterEnhance'
17```
18
19## systemparameter.getSync
20
21getSync(key: string, def?: string): string
22
23Obtains the value of the system parameter with the specified key.
24
25**System capability**: SystemCapability.Startup.SystemInfo
26
27**Parameters**
28
29| Name| Type| Mandatory| Description|
30| -------- | -------- | -------- | -------- |
31| key | string | Yes| Key of the system parameter.|
32| def | string | No| Default value.|
33
34**Return value**
35
36| Type| Description|
37| -------- | -------- |
38| string | Value of the system parameter. If the specified key does not exist, the default value is returned. If no default value has been set, an empty string will be returned.|
39
40**Example**
41
42```ts
43try {
44    var info = systemparameter.getSync("const.ohos.apiversion");
45    console.log(JSON.stringify(info));
46}catch(e){
47    console.log("getSync unexpected error: " + e);
48}
49```
50
51## systemparameter.get
52
53get(key: string, callback: AsyncCallback<string>): void
54
55Obtains the value of the system parameter with the specified key.
56
57**System capability**: SystemCapability.Startup.SystemInfo
58
59**Parameters**
60
61| Name| Type| Mandatory| Description|
62| -------- | -------- | -------- | -------- |
63| key | string | Yes| Key of the system parameter.|
64| callback | AsyncCallback<string> | Yes| Callback used to return the result.|
65
66**Example**
67
68```ts
69try {
70    systemparameter.get("const.ohos.apiversion", function (err, data) {
71    if (err == undefined) {
72        console.log("get test.parameter.key value success:" + data)
73    } else {
74        console.log(" get test.parameter.key value err:" + err.code)
75    }});
76}catch(e){
77    console.log("get unexpected error: " + e);
78}
79```
80
81## systemparameter.get
82
83get(key: string, def: string, callback: AsyncCallback<string>): void
84
85Obtains the value of the system parameter with the specified key. This API uses an asynchronous callback to return the result.
86
87**System capability**: SystemCapability.Startup.SystemInfo
88
89**Parameters**
90
91| Name| Type| Mandatory| Description|
92| -------- | -------- | -------- | -------- |
93| key | string | Yes| Key of the system parameter.|
94| def | string | Yes| Default value.|
95| callback | AsyncCallback<string> | Yes| Callback used to return the result.|
96
97**Example**
98
99```ts
100try {
101    systemparameter.get("const.ohos.apiversion", "default", function (err, data) {
102        if (err == undefined) {
103            console.log("get test.parameter.key value success:" + data)
104        } else {
105            console.log(" get test.parameter.key value err:" + err.code)
106        }
107    });
108}catch(e){
109    console.log("get unexpected error:" + e)
110}
111```
112
113## systemparameter.get
114
115get(key: string, def?: string): Promise<string>
116
117Obtains the value of the system parameter with the specified key. This API uses a promise to return the result.
118
119**System capability**: SystemCapability.Startup.SystemInfo
120
121**Parameters**
122
123| Name| Type| Mandatory| Description|
124| -------- | -------- | -------- | -------- |
125| key | string | Yes| Key of the system parameter.|
126| def | string | No| Default value.|
127
128**Return value**
129
130| Type| Description|
131| -------- | -------- |
132| Promise<string> | Promise used to return the execution result.|
133
134**Example**
135
136```ts
137try {
138    var p = systemparameter.get("const.ohos.apiversion");
139    p.then(function (value) {
140        console.log("get test.parameter.key success: " + value);
141    }).catch(function (err) {
142        console.log("get test.parameter.key error: " + err.code);
143    });
144}catch(e){
145    console.log("get unexpected error: " + e);
146}
147```
148
149## systemparameter.setSync
150
151setSync(key: string, value: string): void
152
153Sets a value for the system parameter with the specified key.
154
155**System capability**: SystemCapability.Startup.SystemInfo
156
157**Parameters**
158
159| Name| Type| Mandatory| Description|
160| -------- | -------- | -------- | -------- |
161| key | string | Yes| Key of the system parameter.|
162| value | string | Yes| Value of the system parameter to set.|
163
164**Example**
165
166```ts
167try {
168    systemparameter.setSync("test.parameter.key", "default");
169}catch(e){
170    console.log("set unexpected error: " + e);
171}
172```
173
174## systemparameter.set
175
176set(key: string, value: string, callback: AsyncCallback<void>): void
177
178Sets a value for the system parameter with the specified key. This API uses an asynchronous callback to return the result.
179
180**System capability**: SystemCapability.Startup.SystemInfo
181
182**Parameters**
183
184| Name| Type| Mandatory| Description|
185| -------- | -------- | -------- | -------- |
186| key | string | Yes| Key of the system parameter.|
187| value | string | Yes| Value of the system parameter to set.|
188| callback | AsyncCallback<void> | Yes| Callback used to return the result.|
189
190**Example**
191
192```ts
193try {
194    systemparameter.set("test.parameter.key", "testValue", function (err, data) {
195    if (err == undefined) {
196        console.log("set test.parameter.key value success :" + data)
197    } else {
198        console.log("set test.parameter.key value err:" + err.code)
199    }});
200}catch(e){
201    console.log("set unexpected error: " + e);
202}
203```
204
205## systemparameter.set
206
207set(key: string, value: string): Promise<void>
208
209Sets a value for the system parameter with the specified key. This API uses a promise to return the result.
210
211**System capability**: SystemCapability.Startup.SystemInfo
212
213**Parameters**
214
215| Name| Type| Mandatory| Description|
216| -------- | -------- | -------- | -------- |
217| key | string | Yes| Key of the system parameter.|
218| value| string | Yes| Value of the system parameter to set.|
219
220**Return value**
221
222| Type| Description|
223| -------- | -------- |
224| Promise<void> | Promise used to return the execution result.|
225
226**Example**
227
228```ts
229try {
230    var p = systemparameter.set("test.parameter.key", "testValue");
231    p.then(function (value) {
232        console.log("set test.parameter.key success: " + value);
233    }).catch(function (err) {
234        console.log(" set test.parameter.key error: " + err.code);
235    });
236}catch(e){
237    console.log("set unexpected error: " + e);
238}
239```
240