72 lines
2.1 KiB
Markdown
72 lines
2.1 KiB
Markdown
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# ipcMain
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The `ipcMain` module, when used in the main process, handles asynchronous and
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synchronous messages sent from a renderer process (web page). Messages sent from
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a renderer will be emitted to this module.
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## Sending Messages
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It is also possible to send messages from the main process to the renderer
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process, see [WebContents.send][webcontents-send] for more information.
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* When sending a message, the event name is the `channel`.
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* To reply a synchronous message, you need to set `event.returnValue`.
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* To send an asynchronous back to the sender, you can use
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`event.sender.send(...)`.
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An example of sending and handling messages between the render and main
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processes:
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```javascript
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// In main process.
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var ipcMain = require('ipc-main');
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ipcMain.on('asynchronous-message', function(event, arg) {
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console.log(arg); // prints "ping"
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event.sender.send('asynchronous-reply', 'pong');
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});
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ipcMain.on('synchronous-message', function(event, arg) {
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console.log(arg); // prints "ping"
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event.returnValue = 'pong';
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});
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```
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```javascript
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// In renderer process (web page).
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var ipcRenderer = require('ipc-renderer');
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console.log(ipcRenderer.sendSync('synchronous-message', 'ping')); // prints "pong"
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ipcRenderer.on('asynchronous-reply', function(event, arg) {
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console.log(arg); // prints "pong"
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});
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ipcRenderer.send('asynchronous-message', 'ping');
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```
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## Listening for Messages
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The `ipcMain` module has the following method to listen for events:
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### `ipcMain.on(channel, callback)`
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* `channel` String - The event name.
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* `callback` Function
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When the event occurs the `callback` is called with an `event` object and a
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message, `arg`.
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## IPC Event
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The `event` object passed to the `callback` has the following methods:
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### `event.returnValue`
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Set this to the value to be returned in a synchronous message.
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### `event.sender`
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Returns the `webContents` that sent the message, you can call
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`event.sender.send` to reply to the asynchronous message, see
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[WebContents.send][webcontents-send] for more information.
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[webcontents-send]: web-contents.md#webcontentssendchannel-args
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