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如何在新增、移除或變更裝置時取得通知 (HTML)

[ 本文的目標對象是撰寫 Windows 執行階段 App 的 Windows 8.x 和 Windows Phone 8.x 開發人員。如果您正在開發適用於 Windows 10 的 App,請參閱 最新文件 ]

這個教學課程說明如何動態列舉裝置。接著,您的應用程式就可以在新增或移除裝置,或是變更裝置屬性時收到通知。

您使用 DeviceWatcher 類別開始裝置列舉。對於找到的每個裝置,DeviceWatcher 會引發 Add 事件,直到找到所有裝置而且列舉完成為止。第一次列舉完成之後,DeviceWatcher 會在新增、更新或移除裝置時繼續引發事件。

您必須知道的事

技術

  • Windows Runtime

先決條件

JavaScript 與 HTML。

指示

步驟 1: 開啟 Microsoft Visual Studio

開啟 Visual Studio 的執行個體。

步驟 2: 建立新專案

在 [新增專案] 對話方塊中,從 [JavaScript]**** > [Windows 市集應用程式] 專案類型選取空白的應用程式。

步驟 3: 插入應用程式 JavaScript 和 HTML

開啟您的 Default.html,然後複製下列的 HTML 到檔案中,取代原始內容。

<!DOCTYPE html>
<html>
<head>
  <title>Device Enumeration Sample</title>
  <meta charset="utf-8" />
  <script src="/js/default.js"></script>
</head>
<body role="application">
    <h1>Device Enumeration Sample</h1>
    <h2 >Input</h2>
    <div >            
            <div >
            <p>This example incrementally enumerates devices, adding them to a list each time a device is found, and also watching for updates.
               Once enumeration is complete, the list of devices is printed.</p> 
                <input type="button" value="Watch(All Devices)" onclick="WatchDevices()"/>
                <br /><br />

                <input type="button" value="Stop" onclick="stopWatcher()"/>
                <br /><br />
            </div>
    </div>

    <h2 > Output</h2>
            <div id="statusMessage"></div>
            <!--  Output -->
            <div  id="output"></div>
</body>
</html>

步驟 4:

將這個程式碼貼到 default.js 中,取代檔案的內容。

    var watcher;
    var isEnumerationComplete = false;
    var deviceArray = new Array(); // Saves the enumeration results

    function WatchDevices() {
        try {
            output.innerHTML = ""; // clear output field

            watcher = 
                Windows.Devices.Enumeration.DeviceInformation.createWatcher();
            // Add event handlers
            watcher.addEventListener("added", onAdded);
            watcher.addEventListener("removed", onRemoved);
            watcher.addEventListener("updated", onUpdated);
            watcher.addEventListener("enumerationcompleted", 
                onEnumerationCompleted);
            watcher.addEventListener("stopped", onStopped);
            // Start enumerating and listening for events
            watcher.start();
        } catch (e) {
            document.getElementById("statusMessage").innerHTML = 
                "Failed to create watcher, error: " + e.message;
        }
    }

    function stopWatcher() {
        try {
            watcher.stop();
        }
        catch (e) {
            document.getElementById("statusMessage").innerHTML = 
                "Failed to stop watcher: " + e.message;
        }
    }

    function onAdded(devinfo) {
        document.getElementById("output").innerHTML += "<p>Device added: " + 
            devinfo.name + "</p>";
        deviceArray.push(devinfo);
        if (isEnumerationComplete) {
            output.innerHTML = ""; // clear output field
            printDeviceArray(document.getElementById("output"));
        }
        
    }

    function onUpdated(devUpdate) {
        document.getElementById("output").innerHTML += "<p>Device updated.</p>";
        for (var i = 0; i < deviceArray.length; i++) {
            if (deviceArray[i].id == devUpdate.id) {
                deviceArray[i].update(devUpdate);
            }
        }
        output.innerHTML = ""; // clear output field
        printDeviceArray(document.getElementById("output"));
    }

    function onRemoved(devupdate) {
        document.getElementById("output").innerHTML += "<p>Device removed.</p>";
        for (var i = 0; i < deviceArray.length; i++) {
            if (deviceArray[i].id == devupdate.id) {
                deviceArray[i].slice(devupdate);
            }
        }
        output.innerHTML = ""; // clear output field
        printDeviceArray(document.getElementById("output"));
    }

    function onEnumerationCompleted(obj) {
        isEnumerationComplete = true;
        document.getElementById("output").innerHTML += 
            "<p>Enumeration Completed.</p>";
        printDeviceArray(document.getElementById("output"));
    }

    function onStopped(obj) {
        document.getElementById("output").innerHTML += "<p>Stopped.</p>";
        if (watcher.status == Windows.Devices.Enumeration.DeviceWatcherStatus.aborted) {
           document.getElementById("output").innerHTML += 
            "<p>Enumeration stopped unexpectedly. </p>";
           document.getElementById("output").innerHTML += 
            "<p>Click the Watch button to restart enumeration.</p>";
        } else if (watcher.status == Windows.Devices.Enumeration.DeviceWatcherStatus.stopped) {
           document.getElementById("output").innerHTML += 
            "<p>You requested to stop enumeration. </p>";
           document.getElementById("output").innerHTML += 
            "<p>Click the Watch button to restart enumeration.</p>";
        }

    }


    // Prints the friendly name of the device interface, 
    // its ID (device interface path), and whether it is enabled.
    function printDevice(deviceInterface, outputDestination) {
        outputDestination.innerHTML += "<p>Name: " + 
            deviceInterface.name + "<p/>"; 
        outputDestination.innerHTML += "<p>Interface ID: " + 
            deviceInterface.id + "<p/>";    
        outputDestination.innerHTML += "<p>Enabled: " + 
            deviceInterface.isEnabled + "<p/>";
        outputDestination.innerHTML += "<br />";
    }

    function printDeviceArray(outputDestination) {
        for (var i = 0; i < deviceArray.length; i++) {
            printDevice(deviceArray[i], outputDestination);
        }
    }

備註

這個範例會以累加方式列舉裝置。只要找到裝置就會將它加入清單,同時也會尋找更新。列舉完成後,應用程式就會列印裝置清單。如果使用者在第一次列舉完成後又新增、更新或移除裝置,應用程式也會列印訊息。

注意  應用程式必須訂閱所有 addedremovedupdated 事件,才能在有裝置新增、移除或更新時收到通知。如果應用程式僅處理 added 事件,則在初次裝置列舉完成之後,若有裝置被新增到系統中,應用程式將不會收到更新。