Question

我正在使用VS2017的asp.net 4.5 Web表单并使用dropdownlist来获取值从数据库中尝试获取值但它一直只给我最高值，所以我在寻求帮助。

我对该值进行绑定的方式是：

protected void Page_Load(object sender, EventArgs e)
{
    var db = new dbContext();
    var CustItem = db.customer.ToList();

    customerDropDownList.DataSource = CustItem;
    customerDropDownList.DataTextField = "cust";
    customerDropDownList.DataValueField = "cust";
    customerDropDownList.DataBind();
}

并且它运行良好并获取customer表中的所有列表并填充id：customerDropDownList中cust列中的数据。然后我尝试通过testBtn从customerDropDownList获取值附加并使用了testLbl

protected void testBtn_Click(object sender, EventArgs e)
{
    testLbl.Text = customerDropDownList.SelectedValue;
}

并且它始终只选择顶部元素。

我怀疑这与asp.net的生命周期有关，我正在研究它但无法找到解决这个问题的明确答案。

有人可以帮我吗？

Answer 1

可能是因为您正在重置每个页面加载的下拉列表。请尝试仅在第一次设置ddlist。

cat /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/ffi-1.9.21/mkmf.log .
package configuration for libffi is not found
have_header: checking for ffi.h... -------------------- no

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.3  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: int main(int argc, char **argv)
4: {
5:   return 0;
6: }
/* end */

"gcc -E -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC  conftest.c -o conftest.i"
conftest.c:3:17: fatal error: ffi.h: No such file or directory
compilation terminated.
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <ffi.h>
/* end */

--------------------

find_header: checking for ffi.h in /usr/local/include,/usr/include/ffi... -------------------- no

"gcc -E -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC  conftest.c -o conftest.i"
conftest.c:3:17: fatal error: ffi.h: No such file or directory
compilation terminated.
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <ffi.h>
/* end */

"gcc -E -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC -I/usr/local/include conftest.c -o conftest.i"
conftest.c:3:17: fatal error: ffi.h: No such file or directory
compilation terminated.
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <ffi.h>
/* end */

"gcc -E -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC -I/usr/include/ffi conftest.c -o conftest.i"
conftest.c:3:17: fatal error: ffi.h: No such file or directory
compilation terminated.
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <ffi.h>
/* end */

--------------------

have_header: checking for shlwapi.h... -------------------- no

"gcc -E -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC  conftest.c -o conftest.i"
conftest.c:3:21: fatal error: shlwapi.h: No such file or directory
compilation terminated.
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <shlwapi.h>
/* end */

--------------------

have_func: checking for rb_thread_blocking_region()... -------------------- no

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.3  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
conftest.c: In function ‘t’:
conftest.c:13:57: error: ‘rb_thread_blocking_region’ undeclared (first use in this function)
 int t(void) { void ((*volatile p)()); p = (void ((*)()))rb_thread_blocking_region; return !p; }
                                                         ^
conftest.c:13:57: note: each undeclared identifier is reported only once for each function it appears in
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
13: int t(void) { void ((*volatile p)()); p = (void ((*)()))rb_thread_blocking_region; return !p; }
/* end */

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.3  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
/tmp/ccv7JcIW.o: In function `t':
/var/lib/gems/2.3.0/gems/ffi-1.9.21/ext/ffi_c/conftest.c:14: undefined reference to `rb_thread_blocking_region'
collect2: error: ld returned 1 exit status
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
13: extern void rb_thread_blocking_region();
14: int t(void) { rb_thread_blocking_region(); return 0; }
/* end */

--------------------

have_func: checking for rb_thread_call_with_gvl()... -------------------- yes

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.3  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
conftest.c: In function ‘t’:
conftest.c:13:57: error: ‘rb_thread_call_with_gvl’ undeclared (first use in this function)
 int t(void) { void ((*volatile p)()); p = (void ((*)()))rb_thread_call_with_gvl; return !p; }
                                                         ^
conftest.c:13:57: note: each undeclared identifier is reported only once for each function it appears in
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
13: int t(void) { void ((*volatile p)()); p = (void ((*)()))rb_thread_call_with_gvl; return !p; }
/* end */

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.3  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
13: extern void rb_thread_call_with_gvl();
14: int t(void) { rb_thread_call_with_gvl(); return 0; }
/* end */

--------------------

have_func: checking for rb_thread_call_without_gvl()... -------------------- yes

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.3  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
conftest.c: In function ‘t’:
conftest.c:13:57: error: ‘rb_thread_call_without_gvl’ undeclared (first use in this function)
 int t(void) { void ((*volatile p)()); p = (void ((*)()))rb_thread_call_without_gvl; return !p; }
                                                         ^
conftest.c:13:57: note: each undeclared identifier is reported only once for each function it appears in
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
13: int t(void) { void ((*volatile p)()); p = (void ((*)()))rb_thread_call_without_gvl; return !p; }
/* end */

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.3.0 -I/usr/include/ruby-2.3.0/ruby/backward -I/usr/include/ruby-2.3.0 -I. -Wdate-time -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.3  -lpthread -lgmp -ldl -lcrypt -lm   -lc"
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
13: extern void rb_thread_call_without_gvl();
14: int t(void) { rb_thread_call_without_gvl(); return 0; }
/* end */

--------------------

extconf.h is:
/* begin */
1: #ifndef EXTCONF_H
2: #define EXTCONF_H
3: #define HAVE_RB_THREAD_CALL_WITH_GVL 1
4: #define HAVE_RB_THREAD_CALL_WITHOUT_GVL 1
5: #define HAVE_FFI_PREP_CIF_VAR 1
6: #define USE_INTERNAL_LIBFFI 1
7: #define RUBY_1_9 1
8: #endif
/* end */

Answer 2

您在页面加载事件中缺少Page.IsPostBack

更多关于Ispostback here

使用您的代码，您没有注意到您的下拉列表在点击时加倍了吗？

protected void Page_Load(object sender, EventArgs e)
{
    if(!Page.IsPostBack)
    {
        var db = new dbContext();
        var CustItem = db.customer.ToList();

        customerDropDownList.DataSource = CustItem;
        customerDropDownList.DataTextField = "cust";
        customerDropDownList.DataValueField = "cust";
        customerDropDownList.DataBind();
    }
}

确保只加载一次下拉列表。您的页面加载也将在按钮单击时调用。

保持休息点并玩转！祝你好运

无法从数据库绑定的下拉列表中获取值

2 个答案: