如何建立清单 <String> 从清单中 <Map<String, String> &gt;在Dart中？

Question

I have a Map that looks like this

{
    title: "Hello world",
    images: [
        { url: "http://example.com/image1" },
        { url: "http://example.com/image2" },
        { url: "http://example.com/image3" }
    ]
}

and I need a List<String> of the images that looks like this

[
    "http://example.com/image1",
    "http://example.com/image2",
    "http://example.com/image3"
]

My current code looks like this

List<String> images = [];
if( map['images'] is List<dynamic> ) {
    map['images'].forEach((v) {
        if (null != v['url'])
            images.add(v['url']);
    });
}

It works good, but I am curious if there is a one-liner that would accomplish the same thing in a neat (and error safe) way?

Answer 1

var list = map['images'].map((innerMap) => innerMap['url']).toList()

Answer 2

I guess you are looking for something like this:

var images = map['images'].where((m) => m['url'] != null).map((value) => value['url']).toList();

First we select all the items from map that do not contain a null field for url . Then we map these url values to a new List .