README.md
1# Observer
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3### Overview
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5This sample demonstrates how to use observer APIs to subscribe to events of network status, signal status, call status, cellular data, and SIM card status changes.
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10### Concepts
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12`@ohos.telephony.observer`
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14 A module that allows you to register observers to subscribe to events of mobile network, signal, call, and SIM card status changes.
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16### Required Permissions
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18The following permission must be declared in the `module.json5` file:
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20**ohos.permission.GET_NETWORK_INFO**: Obtains the network status.
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22**ohos.permission.READ_CALL_LOG**: Obtains the call status.
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24### How to Use
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261. Open the application and enable all event subscription switches.
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282. Enable or disable the mobile network once to trigger a network status change.
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303. Make a call to trigger a call status change.
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324. Remove and insert the SIM card to trigger a SIM card status and signal status change.
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345. Touch the **Details** button. A page is displayed, showing the related status change events.
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36### Constraints
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381. This sample can only be run on standard-system devices.
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402. This sample demonstrates the stage model, which supports only API version 9.
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423. This sample requires DevEco Studio 3.0 Beta4 (Build Version: 3.0.0.992, built on July 14, 2022) to compile and run.
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