ScrollTop不适用于动态生成的元素

Question

我正在尝试创建一个聊天系统（如Facebook），用户点击在线用户的名称，将出现一个聊天框。 _chatbox是使用javascript动态生成的。它将向下滚动到最后一条消息。聊天框和消息加载/显示成功，但向下滚动功能不起作用...为什么？

//displays the popups. Displays based on the maximum number of popups that can be displayed on the current viewport width
function display_popups() {
  //code for popup here
}

//creates markup for a new popup. Adds the id to popups array.
function register_popup(id, name) {

  var element = '<div class="popup-box chat-popup" id="' + id + '">';
  element = element + '<div class="popup-head">';
  element = element + '<div class="popup-head-left">' + name + '</div>';
  element = element + '<div class="popup-head-right"><a href="javascript:close_popup(\'' + id + '\');">&#10005;</a></div>';
  element = element + '<div style="clear: both"></div></div><div class="popup-messages"></div></div>';
  document.getElementsByTagName("body")[0].innerHTML = document.getElementsByTagName("body")[0].innerHTML + element;
  calculate_popups();
  scrollDown(id);
}

//scroll down to the last message
function scrollDown(id) {
  var messages = document.getElementById(id);
  messages.scrollTop = messages.scrollHeight;
}

//calculate the total number of popups suitable and then populate the toatal_popups variable.
function calculate_popups() {
  //calculate popups here
}

<div class="sidebar-name">
  <a href="javascript:register_popup('ind', 'Indiana Pacers');">
    <img width="30" height="30" src="img/ind.png" />
    <span>Indiana Pacers</span>
  </a>
</div>

Answer 1

它有效，但你似乎选择了错误的元素。我调整了你的代码，以便我可以演示正在发生的事情。这里的可滚动元素是消息容器（类“.popup-messages”），而不是弹出窗口本身。

您需要调整此代码，因为我直接选择了.popup-messages元素，但您可能想要选择弹出窗口中特定的元素。

//displays the popups. Displays based on the maximum number of popups that can be displayed on the current viewport width
function display_popups()
{
    //code for popup here
}

//creates markup for a new popup. Adds the id to popups array.
function register_popup(id, name)
{

    var element = '<div class="popup-box chat-popup" id="'+ id +'">';
    element = element + '<div class="popup-head">';
    element = element + '<div class="popup-head-left">'+ name +'</div>';
    element = element + '<div class="popup-head-right"><a href="javascript:close_popup(\''+ id +'\');">&#10005;</a></div>';
    element = element + '<div style="clear: both"></div></div><div class="popup-messages"><p>message</p><p>message</p><p>message</p><p>message</p><p>message</p><p>message</p><p>message</p><p>message</p><p>message</p><p>message</p><p>message</p><p>last message</p></div></div>';
    document.getElementsByTagName("body")[0].innerHTML = document.getElementsByTagName("body")[0].innerHTML + element;    
    calculate_popups();
    scrollDown(id);
}

//scroll down to the last message
function scrollDown(id)
{
    var messages = document.getElementsByClassName('popup-messages')[0];
    messages.scrollTop = messages.scrollHeight;
}

//calculate the total number of popups suitable and then populate the toatal_popups variable.
function calculate_popups()
{
   //calculate popups here
}

window.onload = function(){
  register_popup('test', 'testName');
};

.popup-messages {
  height: 100px;
  overflow-y: scroll;
}

<div class="sidebar-name">
    <a href="javascript:register_popup('ind', 'Indiana Pacers');">
        <img width="30" height="30" src="img/ind.png" />
        <span>Indiana Pacers</span>
    </a>
</div>

Answer 2

为什么使用innerHTML而不是创建元素？

您可以尝试使用Javascript创建元素并手动将其添加到DOM，如：

var popupBox = document.createElement("div");
// Set properties
var popupHead = document.createElement("div");
// Set properties
popupBox.appendChild(popupHead);
// etc. etc

// Then add it to DOM
document.getElementsByTagName("body")[0].appendChild(element)

// This should work now
calculate_popups();
scrollDown(id);

我认为设置innerHtml并将其转换为DOM比函数调用晚处理。

阅读使用Javascript创建元素：https://developer.mozilla.org/en-US/docs/Web/API/Document/createElement