错误“使用未分配的局部变量”？

Question

The error is in "search, adapter.GetData(search, null, null, TextBox1.Text, null);" which is a parameter, but already initialize the variable, in the other parameters does not mark error. why?

string search;
adapter.GetData(search, null, null, TextBox1.Text, null);
this.gridview.DataBind();
this.gridview.DataSource = adapter.GetData(search, null, null, TextBox1.Text,null);

Answer 1

Initialize a variable means assign it an initial value

string search; // not initialized, You define it's type and it's name. 
string search = "something"; //initialized 

You can even set null value to search like string search =null; then compiler will not warn you because you are intentionally doing it.

if you need to search and bind returned search result to gridview

search = "set some value here";
//set data source
this.gridview.DataSource =adapter.GetData(search, null, null, TextBox1.Text, null);
//now bind the gridview 
this.gridview.DataBind();

Answer 2

As it is right now, search is not a parameter, it is a local variable. That local variable does not have a value assigned to it, therefore the error. If you just want to test it, do something like

string search = "Any value you want to test";

Answer 3

string search;

Is a declaration while

string search = "foo";

is an assignment.

Null is not a variable, and TextBox.Text1 has a value. You are getting that error because while the search variable is declared, it does not have a value assigned to it.