Flutter使用html解析从img src获取数据

我必须获取“ <img src =“值。我怎样才能做到这一点？我尝试了这个：

responseBody = responseBody.substring(responseBody.indexOf('<img src=""'));
var lt = responseBody.substring(0, responseBody.indexOf('" />'));

还有这个：

for (var i = 0; i < count; i++) {
  print(document.getElementsByClassName("firma-isim")[i].getElementsByTagName("img")[0].getElementsByTagName("src").first;
}

但是没有用。是否有捷径可寻？我怎样才能做到这一点？谢谢。

HTML：

<div class="populer-firmalar">
    <span class="firma-sol" data-kaydir=".pop-firma,sol,1"><i class="fa fa-angle-left"></i></span>
    <span class="firma-sag" data-kaydir=".pop-firma,sag,1"><i class="fa fa-angle-right"></i></span>
    <div class="populer-firma-holder">
        <ul class="pop-firma">
                            <li class="active">
                <div class="firma-resim">
                    <a href="https://kimbufirma.com/firma/a3-dijital-web-tasarim-ve-yazilim-ajansi/"><img src="https://kimbufirma.com/firma/wp-content/uploads/2021/02/a3-dijital-web-tasarim-ve-yazilim-ajansi.cropped.270x200.jpg" alt="A3 DİJİTAL | WEB TASARIM VE YAZILIM AJANSI" width="270" height="200"></a>
                </div>