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How Can I Improve the Efficiency of Loading Dropdown Lists for States and Cities?
How Can I Improve the Efficiency of Loading Dropdown Lists for States and Cities?
Jan 28, 2025 pm 06:11 PM
The method of loading the state -drop -down list directly when loading on the page is inefficient. This article will introduce more efficient and best practices.
Recommended method:
<.> 1. Use the view model:
Create a view model, including Stateid, Cityid, Statelist, and CityList properties. This helps package data and provides strong types.<.> 2. Use non -invasive javascript:
Avoid using the Inner Union JavaScript in the mark. Instead, the non -invasive JavaScript is used to separate HTML and behavior.
Drop -down list Modification:
Cache optimization:
@Html.DropDownList(m => m.StateID, States, "選擇州") //移除onchange屬性 @Html.DropDownListFor(m => m.CityID, Cities, "選擇城市") //保留默認(rèn)IDIf multiple items are rendered, and their options may include cities from the same state, cache can be used to avoid repeated API calls.
<需> Ajax replacement method:
const url = '@Url.Action("GetCities", "Home")'; // 使用助手方法
const citiesDropdown = $('#CityID'); // 緩存元素
$('#StateID').change(function () {
$.getJSON(url, { id: $(this).val() }, function (response) {
// 清空并添加默認(rèn)（null）選項(xiàng)
citiesDropdown.empty().append($('<option></option>').val('').text('請選擇'));
$.each(response, function (index, item) {
citiesDropdown.append($('<option></option>').val(item.Value).text(item.Text));
});
});
});
If the number of states and cities is limited, all cities can be passed to the view and assigned them to the JavaScript array. However, this may lead to a long time of the initial loading. <控> In the controller:
const cache = {};
$('#StateID').change(function () {
const selectedState = $(this).val();
if (cache[selectedState]) {
// 從緩存中渲染選項(xiàng)
// ... 使用cache[selectedState]渲染城市下拉列表
} else {
$.getJSON(url, { id: selectedState }, function (response) {
// 添加到緩存
cache[selectedState] = response;
// ... 使用response渲染城市下拉列表
});
}
}); in the view (javascript):
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