Question

我正在尝试将设备就绪事件用于phonegap 3 helloworld默认应用。

HTML

<html>
<head>
    <meta charset="utf-8" />
    <meta name="format-detection" content="telephone=no" />
    <meta name="viewport" content="user-scalable=no, initial-scale=1, maximum-scale=1, minimum-scale=1, width=device-width, height=device-height, target-densitydpi=device-dpi" />
    <link rel="stylesheet" type="text/css" href="css/index.css" />
    <title>Hello World</title>
</head>
<body>
    <div class="app">
        <h1>PhoneGap</h1>
        <div id="deviceready" class="blink">
            <p class="event listening">Connecting to Device</p>
            <p class="event received">Device is Ready</p>
        </div>
    </div>
    <script type="text/javascript" src="phonegap.js"></script>
    <script type="text/javascript" src="js/index.js"></script>
    <script type="text/javascript">
        app.initialize();
    </script>
</body>

的javascript

var app = {
// Application Constructor
initialize: function() {
    this.bindEvents();
},
// Bind Event Listeners
//
// Bind any events that are required on startup. Common events are:
// 'load', 'deviceready', 'offline', and 'online'.
bindEvents: function() {
    document.addEventListener('deviceready', this.onDeviceReady, false);
},
// deviceready Event Handler
//
// The scope of 'this' is the event. In order to call the 'receivedEvent'
// function, we must explicity call 'app.receivedEvent(...);'
onDeviceReady: function() {
    app.receivedEvent('deviceready');
    alert('welcome!');
},
// Update DOM on a Received Event
receivedEvent: function(id) {
    var parentElement = document.getElementById(id);
    var listeningElement = parentElement.querySelector('.listening');
    var receivedElement = parentElement.querySelector('.received');

    listeningElement.setAttribute('style', 'display:none;');
    receivedElement.setAttribute('style', 'display:block;');

    console.log('Received Event: ' + id);
}
};

此代码正常运行，当我打开应用程序时会触发我的欢迎警报。但是，如果我注释掉其中任何一行：

<p class="event listening">Connecting to Device</p>
<p class="event received">Device is Ready</p>

欢迎警报将不再触发。这里发生了什么我不知道phonegap用什么机制来创建这种行为？

Answer 1

这里的问题不在于phonegap，而是导致错误的receivedEvent函数。如果您在致电alert之前移动receivedEvent，则应该会看到deviceready事件仍然正常启动。

实际问题是该行

var listeningElement = parentElement.querySelector('.listening');

从DOM中获取<p class="event listening">..</p>元素。由于您删除了该元素，listeningElement将为null。现在来电

listeningElement.setAttribute('style', 'display:none;');

因此而失败。

奇怪的phonegap设备准备好的事件行为

1 个答案: