往Alert中添加Command

最新推荐文章于 2025-08-26 10:14:09 发布

最新推荐文章于 2025-08-26 10:14:09 发布 · 149 阅读

文章标签：

#C #C++ #C#

JavaME 专栏收录该内容

28 篇文章

订阅专栏

本文探讨了Java程序中Alert组件的行为特点，特别是在出现IOException时如何通过设置不同的命令来改变Alert的行为。当Alert上只有一个命令时，可以设置超时时间，在时间到达后自动执行该命令；若有多个命令，则Alert将变为模态对话框，必须手动选择命令。

} catch (IOException e) {
	Alert alert = new Alert("地图; IOException", "网络连接捕获住异常：" + e.toString() + "\n\n" + "程序在10秒后会自动退出", null, AlertType.WARNING);
	final Command exitCommand = new Command("退出", Command.EXIT, 1);
	alert.addCommand(exitCommand);
	alert.setTimeout(10 * 1000);
	alert.setCommandListener(new CommandListener() {
		public void commandAction(Command c, Displayable d) {
			if (exitCommand == c) {
				dispatcher.exit(true);
			}
		}
	});
	dispatcher.display.setCurrent(alert);
}

这一段代码如果没有alert.setTimeout(10*1000)这条语句，不经点击exitCommand按钮，程序会自动执行dispatcher.exit(true); 纠结了一个上午，解释如下：

When it is created, an Alert implicitly has the special Command DISMISS_COMMAND present on it. If the application adds any other Commands to the Alert, DISMISS_COMMAND is implicitly removed. If the application removes all other Commands, DISMISS_COMMAND is implicitly restored. Attempts to add or remove DISMISS_COMMAND explicitly are ignored. Thus, there is always at least one Command present on an Alert.
If there are two or more Commands present on the Alert, it is automatically turned into a modal Alert, and the timeout value is always FOREVER. The Alert remains on the display until a Command is invoked. If the Alert has one Command (whether it is DISMISS_COMMAND or it is one provided by the application), the Alert may have the timed behavior as described above. When a timeout occurs, the effect is the same as if the user had invoked the Command explicitly.