如何檢查單選按鈕列表中的單選按鈕是否被選中

Question

早上好

我在遍歷單選按鈕列表以檢查是否使用 Javascript 時遇到了一些困難。 使用 C# Asp.net 的過程相對簡單，但使用 Javascript 我有點掙扎。

這是我與 C# 一起使用的代碼，用於檢查是否選擇了單選按鈕。

protected void Button1_Click(object sender, EventArgs e)
{
    string radValue = RadioButtonList1.SelectedValue.ToString();

    if (radValue == "")
    {
        lblError.Text = "Please select neigbourhood";
    }
    else
    {
        lblError.Text = "You come from " + radValue;
    }

}

我與 javascript 一起使用的代碼有點錯誤，我希望它可以得到糾正。

var radNeighbourhood;

for(var loop=0; loop < document.subscribeForm.myRadio.length; loop++)
{
    if(document.subscribeForm.myRadio[loop].checked == true)
    {
        radNeighbourhood = document.subscribeForm.myRadio[loop].value;
        break;

    }
    else
    {
        alert("Please select a neigbourhood");
        return false;
    }
}
return true;    

親切的問候阿里安

Answer 1

您可能正在尋找類似的東西：

var radNeighbourhood;
for (var loop=0; loop < document.subscribeForm.myRadio.length; loop++)
{
    if (document.subscribeForm.myRadio[loop].checked == true)
    {
        radNeighbourhood = document.subscribeForm.myRadio[loop].value;
        break;
    }
}

if (!radNeighbourhood)
{
    alert("Please select a neighbourhood");
    return false;
}

alert("You come from " + radNeighbourhood);
return true;

Answer 2

我做了一個你在這里問的小樣本。 http://jsfiddle.net/mZhQ9/2/

編輯：分析

var radioButtons = document.subscribeForm.myRadio; //it is crucial to store the DOM information in a variable instead of grabbing it, each single time. (DOM operations are EXTREMELY slow)
var len = radioButtons.length; //same as before
var found = false; //our flag - whether something was found or not

while( len-- > 0 ) { //decreasing the counter (length of radio buttons)
    if( radioButtons[len].checked === true ) { //if we find one that is checked
        found = true; //set the flag to true
        break; //escape the loop
    }
} 

if( found ) { //if our flag is set to true
    alert( radioButtons[len].value );
    return radioButtons[len].value; //return the value of the checked radiobutton (remember, when we broke from the While-loop, the len value remained at the 'checked' radio button position)
}
else { 
    alert( "Please select a neigbourhood" );
    return false; //else return false
}

編輯 2：作為旁注，請注意在循環中使用“for(var loop=0;loop < document.subscribeForm.myRadio.length;loop++)”DOM 操作。 loop < document.subscribeForm.myRadio.length 條件每次都會檢查文檔並抓取單選按鈕，從而導致大量不必要的開銷。