为什么当用户从下拉列表中选择不同的选项时，Line1Co.Value始终保持为0？
这是我的HTML：
<asp:DropDownList ID="HandLine1Size" runat="server" AutoPostBack="true" Width="110px">
<asp:ListItem Value="1">1.75</asp:ListItem>
<asp:ListItem Value="1.5625">2</asp:ListItem>
<asp:ListItem Value="2.25">2.5</asp:ListItem>
<asp:ListItem Value="3.0625">3</asp:ListItem>
<asp:ListItem Value="0">No handline</asp:ListItem>
</asp:DropDownList
<asp:HiddenField ID="Line1Co" runat="server" />
<br />
<%= Line1Co.Value %>
这是我的代码背后：
Protected Sub Line1Co_ValueChanged(sender As Object, e As EventArgs) Handles Line1Co.ValueChanged
If HandLine1Size.SelectedValue = "1" Then Line1Co.Value = "12" Else
If HandLine1Size.SelectedValue = "1.5625" Then Line1Co.Value = "8" Else
If HandLine1Size.SelectedValue = "2.25" Then Line1Co.Value = "2" Else
If HandLine1Size.SelectedValue = "3.0625" Then Line1Co.Value = "0.75" Else
Line1Co.Value = "20"
End Sub
答案 0 :(得分：0)
我在你的代码中看到两个问题：
您应该处理DropDownList的#include <iostream>
#include <string>
#include <stdio.h>
#include <ctype.h>
using namespace std;
void sort(char letters[], int integers[], int size);
void swap_letters(char& first, char& second, int& int1, int& int2);
int index_of_largest(const int integers[], int start_index, int number_used);
int main(){
const int MAX_CHARS = 200;
char letters[MAX_CHARS] = {'\0'};
int integers[MAX_CHARS] = {'\0'};
int index, size = 0;
char character;
cout << "Enter text:" << endl;
cin.get(character);
character = tolower(character);
while (character!= '.' && size < MAX_CHARS){
if(isalpha(character)){
index = 0;
while (index < size){
if(letters[index] == character)
break;
else
index++;
}
if (index < size){
integers[index] = integers[index] + 1;
}
else{
letters[index] = character;
integers[index] = 1;
size++;
}
}
cin.get(character);
character = tolower(character);
}
letters[index] = tolower(letters[index]);
sort(letters, integers, size);
cout << "Frequencies:"<< endl;
for(int i = 0; i < size; i++){
cout << letters[i] << " " << integers[i] << endl;
}
return 0;
}
void sort(char letters[], int integers[], int size){
for (int i = 0; i < size -1; i++){
int j = index_of_largest(integers, i, size);
swap_letters(letters[i], letters[j], integers[i], integers[j]);
}
}
void swap_letters(char& first, char& second, int& int1, int& int2){
char temp_char = first;
first = second;
second = temp_char;
int temp_int = int1;
int1 = int2;
int2 = temp_int;
}
int index_of_largest(const int integers[], int start_index, int number_used){
int max_int = integers[start_index];
int max_int_index = start_index;
for (int index = start_index + 1; index < number_used; index++){
if (integers[index] > max_int){
max_int = integers[index];
max_int_index = index;
}
}
return max_int_index;
}
而不是HiddenField的SelectedIndexChanged事件。
单行ValueChanged语句对我来说看起来不对，最后是if。始终执行最后一行，并且在所有情况下将值设置为Else。
<小时/> 以下是实现目标的几种方法。
使用单行"20"语句：
if使用多行Protected Sub HandLine1Size_SelectedIndexChanged(sender As Object, e As EventArgs) Handles HandLine1Size.SelectedIndexChanged
Line1Co.Value = "20"
If HandLine1Size.SelectedValue = "1" Then Line1Co.Value = "12"
If HandLine1Size.SelectedValue = "1.5625" Then Line1Co.Value = "8"
If HandLine1Size.SelectedValue = "2.25" Then Line1Co.Value = "2"
If HandLine1Size.SelectedValue = "3.0625" Then Line1Co.Value = "0.75"
End Sub
声明：
if使用Protected Sub HandLine1Size_SelectedIndexChanged(sender As Object, e As EventArgs) Handles HandLine1Size.SelectedIndexChanged
If HandLine1Size.SelectedValue = "1" Then
Line1Co.Value = "12"
ElseIf HandLine1Size.SelectedValue = "1.5625" Then
Line1Co.Value = "8"
ElseIf HandLine1Size.SelectedValue = "2.25" Then
Line1Co.Value = "2"
ElseIf HandLine1Size.SelectedValue = "3.0625" Then
Line1Co.Value = "0.75"
Else
Line1Co.Value = "20"
End If
End Sub
声明：
Select