从Dart中的嵌套聚合物元素中捕获异常

Mike Mitterer 发表于 Dev

迈克·米特勒

我不知道如何捕获嵌套元素引发的异常。

我想要的是这样的：

<error-handler>
    <hard-worker></hard-worker>
</error-handler>

例如，该想法是在勤奋的工作中发出REST请求。当然，如果努力工作的人从REST服务器中获取错误，它将进行自己的错误处理。但最后它必须在某处/以某种方式显示错误消息。错误处理程序被认为是向用户显示错误（异常）的人。错误处理程序应该是可变的。例如，可能是错误处理程序日志消息或错误处理程序显示弹出窗口。

迈克·米特勒

我在GitHub上更新了Polymer-Sample。它显示了两种讨论的方法：基于Eventbus的方法（已经存在）和新的DOM-Event方法。（我更喜欢的一种-清洁得多）

工作示例（Chrome）
https://rawgithub.com/MikeMitterer/DART-Sample-PolymerHelloWorld/master/build/index.html

代码：https：
//github.com/MikeMitterer/DART-Sample-PolymerHelloWorld/tree/master/web

关于我所做的一些详细信息：
index.html

<!DOCTYPE html>
<html>
<head>
    <link rel="import" href="hello-world/hello-world.html">
    <link rel="import" href="event-handler/event-handler.html">
    <link rel="import" href="stopwatch/stopwatch.html">
    <script type="application/dart">export 'package:polymer/init.dart';</script>
</head>
<body>

    <h1>Hi first world!</h1>
    <!-- event-handler should show some events coming in from hello-world -->
    <event-handler>
        <hello-world></hello-world>
    </event-handler>

    <script src="packages/browser/dart.js"></script>
    </body>
</html>

hello-
world.html如果您单击“触发事件”按钮，则会触发事件。这也可能是错误消息...

<!DOCTYPE html>
<polymer-element name="hello-world">
    <template>
        <button on-click="{{increment}}">Click Me</button>
        <button on-click="{{fireevent}}">Fire an event (received by event-handler)</button>

        <p>Hello from inside a custom element! Clicks: {{count}}</p>
    </template>
    <script type="application/dart" src="hello-world.dart"></script>
</polymer-element>

hello-world.dart

import 'package:polymer/polymer.dart';
import 'package:event_bus/event_bus.dart';
import 'package:PolymerHelloWorld/globaleventbus.dart';
import 'dart:html';
import 'dart:math';
import 'package:json/json.dart' as JSON;

@CustomTag('hello-world')
class HelloWorldElement extends PolymerElement {
    final EventBus _eventbus = new GlobalEventBus();

    @observable int count = 0;

    HelloWorldElement.created() : super.created();

    void increment(Event e, var detail, Node target) {
        count += 1;
        _eventbus.fire(GlobalEventBus.basicClickEvent,"Test");
    }

    void fireevent(Event e, var detail, Node target) {
        final Random random = new Random();
        final Map json = { 'response' : 'Hi, this is a message', 'random' : random.nextInt(100)};

        // Fires a JSON-Message 
        fire("hello-event",detail: JSON.stringify(json));
    }
}

event-handler.html接收“你好事件”的模板

<!DOCTYPE html>
<polymer-element name="event-handler" on-hello-event="{{handleHelloEvent}}">
    <template>
        <style>
            .error { color: red; }
        </style>
        <p class="error">EventHandler (Shows hello-world events!) Message: {{response}}, Random number: {{randomnumber}}</p>
        <content></content>
    </template>
    <script type="application/dart" src="event-handler.dart"></script>
</polymer-element>

event- handler.dart实现在相应模板中定义的handleHelloEvent

import 'package:polymer/polymer.dart';
import 'package:json/json.dart' as JSON;

@CustomTag('event-handler')
class EventHandler  extends PolymerElement {

    @observable String response = "";
    @observable int randomnumber = 0;

    EventHandler.created() : super.created();

    void handleHelloEvent(Event e, var detail, Node target) {
        final Map json = JSON.parse(detail);

        response = json['response'];
        randomnumber = json['random'];

        // Log to console 
        print("Received event! $detail");
    }
}