淘汰赛数据绑定问题

Question

I have a dropdownlist with data-bind;

<asp:DropDownList ID="cmbType" Runat="server" AutoPostBack="False" data-bind="value: moveType">
  <asp:ListItem Value="">-- Please Select --</asp:ListItem>
  <asp:ListItem Value="0">Car</asp:ListItem>
  <asp:ListItem Value="1">Air</asp:ListItem>
</asp:DropDownList>

also I have

var viewModel = {
  this.moveType = ko.observable(MoveType);

};
ko.applyBindings(new ViewModel());​

where "MoveType" is 0 or 1. This seems to be working fine but only partly. Everything is fine and value from dropdown are selected correctly ONLY if "MoveType" = 1. In case if MoveType = 0, it don't want to select "Car" and instead selected option will be "-- Please Select --" with value "".

The question is simple, why? What am I missing? I can't understand it.

Answer 1

Are You sure that You are not getting any errors in console?

I changed your code into :

var MoveType=1;
var ViewModel = function() {
    this.moveType = ko.observable(MoveType);       
};    
ko.applyBindings(new ViewModel()); // This makes Knockout get to work

and now its seems to work: you can test it Here

Answer 2

"car" has a value of 0 in your drop down list (look at your Value attributes). That is why 0 causes "car" to be selected. If you want to select "-- Please Select --", you need to set the value to an empty string "" .

This in turn implies that your javascript moveType and thus also your C# MoveType must be a string rather than a number, since "" is not a valid number.

To prevent that I suggest you number your options differently: use Value="1" for car and Value="2" for air. Then your "please select" option gets Value="0" .