2019-07-09

项目需要在HTML5 Android App中加入对返回键的处理，发现直接在Activity中加返回键处理代码不起作用，分析cordova源码发现返回键已经被WebView处理掉了，所以只能在js中处理返回键了！

<pre class="brush:java;" style="font-family: "Courier New", monospace; font-size: 12px; margin: 0px 0px 1em; width: 630px; overflow: auto; padding: 10px 0px;"> @Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
if (exit > 1) {
finish();
} else {
Toast.makeText(this, R.string.toast_exit, Toast.LENGTH_SHORT)
.show();
exit++;
}
return true;
} else {
return super.onKeyDown(keyCode, event);
}
}
</pre>

在继承了CordovaActivity的Activity中，上面的代码是不会起作用的，因为WebView已经处理了返回键事件，并退出Activity了

<pre class="brush:java;" style="font-family: "Courier New", monospace; font-size: 12px; margin: 0px 0px 1em; width: 630px; overflow: auto; padding: 10px 0px;"> /*
* Android 2.x needs to be able to check where the cursor is. Android 4.x does not
*
* (non-Javadoc)
* @see android.app.Activity#onKeyDown(int, android.view.KeyEvent)
*/

@Override
public boolean onKeyDown(int keyCode, KeyEvent event)
{
    //Determine if the focus is on the current view or not
    if (appView != null && appView.getFocusedChild() != null && (keyCode == KeyEvent.KEYCODE_BACK || keyCode == KeyEvent.KEYCODE_MENU)) {
                return appView.onKeyDown(keyCode, event);
    }
    else
        return super.onKeyDown(keyCode, event);
}

</pre>

CordovaActivity源码中的返回键处理代码

下面的代码可以响应后退按钮，并提示用户再次点击才退出。
如果3秒后没有点击则重新注册事件。

注意：window.plugins.ToastPlugin.show_short()是显示toast消息的插件!

代码：

<pre class="brush:java;" style="font-family: "Courier New", monospace; font-size: 12px; margin: 0px 0px 1em; width: 630px; overflow: auto; padding: 10px 0px;">// 等待加载PhoneGap
document.addEventListener("deviceready", onDeviceReady, false);
// PhoneGap加载完毕
function onDeviceReady() {
//按钮事件
document.addEventListener("backbutton", eventBackButton, false); //返回键
document.addEventListener("menubutton", eventMenuButton, false); //菜单键
document.addEventListener("searchbutton", eventSearchButton, false); //搜索键
}

//返回键
function eventBackButton(){
//confirm("再点击一次退出!");
window.plugins.ToastPlugin.show_short('再点击一次退出!');
document.removeEventListener("backbutton", eventBackButton, false); //注销返回键
//3秒后重新注册
var intervalID = window.setInterval(
function() {
window.clearInterval(intervalID);
document.addEventListener("backbutton", eventBackButton, false); //返回键
},
3000
);
}
//菜单键
function eventMenuButton(){
window.plugins.ToastPlugin.show_short('点击了 菜单 按钮!');
}
//搜索键
function eventSearchButton(){
window.plugins.ToastPlugin.show_short('点击了 搜索 按钮!');
}</pre>