c# - Add Rows In a empty dataGrid -

i building mvvm - wpf application. have few datagrids crud operations work fine.

now, want datagrid empty @ beginning , of course can add rows. can fill when click save, nothing saved.

why?

viewmodel:

public class invoiceviewmodel : viewmodelbase {     public context ctx = new context();     public invoiceviewmodel()     {         this.collection = new observablecollection<invoice>();     }     private observablecollection<invoice> collection;     public observablecollection<invoice> collection     {                 {             return collection;         }         set         {             collection = value;             onpropertychanged("collection");         }     }     private invoice _selected;     public invoice selected     {                 {             return _selected;         }         set         {             _selected = value;             onpropertychanged("selected");         }     }     private void get()     {         ctx.invoices.tolist().foreach(invoice => ctx.invoices.local.add(invoice));;         collection = ctx.invoices.local;     }     private void save()     {         foreach (invoice item in collection)         {             if (ctx.entry(item).state == system.data.entity.entitystate.added)             {                 ctx.invoices.add(item);             }         }         ctx.savechanges();     }     private void delete()     {         var id = selected;         var invoice = (from in ctx.invoices                     i.idinvoice == id.idinvoice                     select i).singleordefault();         collection.remove(invoice);     }      #region "command"     // private icommand getcommand;     private icommand savecommand;     private icommand removecommand;      /*public icommand getcommand     {                 {             return getcommand ?? (getcommand = new relaycommand(p => this.get(), p => this.canget()));         }     }     private bool canget()     {         return true;     }*/     public icommand savecommand     {                 {             return savecommand ?? (savecommand = new relaycommand(p => this.save(), p => this.cansave()));         }     }     private bool cansave()     {         return true;     }     public icommand deletecommand     {                 {             return removecommand ?? (removecommand = new relaycommand(p => this.delete(), p => this.candelete()));         }     }     public bool candelete()     {         if (selected != null)             return true;         else             return false;     }     #endregion } 

view:

<page.resources>     <local:invoiceviewmodel x:key="invoice" />     <local:shopviewmodel x:key="shop" />     <local:supplierviewmodel x:key="supplier" />     <local:productviewmodel x:key="product" />     <datatemplate x:key="productdatatemplate">         <textblock text="{binding product}" />     </datatemplate> </page.resources> <datagrid x:name="datagridinvoice"           margin="5"           grid.row="1"           itemssource="{binding collection}"           autogeneratecolumns="false"           selecteditem="{binding selected, mode=twoway}"           selectionmode="extended"           selectionunit="fullrow">     <datagrid.columns>         <datagridtextcolumn x:name="datagridtextcolumn"                             header="supplier invoice nb"                             width="*" />         <datagridcomboboxcolumn header="ref supplier"                                 itemssource="{binding products, source={staticresource supplier}, mode=oneway}"                                 displaymemberpath="refsup"                                 selectedvaluebinding="{binding refsupp}"                                 selectedvaluepath="refsup"                                 width="*" />         <datagridtextcolumn header="unit"                             binding="{binding unit, updatesourcetrigger=propertychanged, mode=twoway}"                             width="*" />         <datagridtextcolumn header="quantity"                             binding="{binding quantity, updatesourcetrigger=propertychanged, mode=twoway}"                             width="*" />         <datagridtextcolumn header="prix/moq"                             binding="{binding unitprice, updatesourcetrigger=propertychanged, mode=twoway}"                             width="*" />         <datagridtextcolumn header="total price"                             binding="{binding totalprice, updatesourcetrigger=propertychanged, mode=twoway}"                             width="*" />     </datagrid.columns> </datagrid> <stackpanel orientation="horizontal">     <button  x:name="btndelete"              content="delete"              command="{binding deletecommand}"              horizontalalignment="center"              margin="100,5,5,5"              width="85" />     <button  x:name="btnadd"              content="save"              command="{binding savecommand}"              horizontalalignment="center"              margin="20,5,5,5"              width="85" /> </stackpanel> 

you have method binds collection cached local of entity set. without binding, it's harder save added items:

private void get() {         ctx.invoices.tolist().foreach(invoice => ctx.invoices.local.add(invoice));;         collection = ctx.invoices.local; } 

in fact can load invoices , cache local:

private void get() {    ctx.invoices.load();    collection = ctx.invoices.local; } 

however said want empty data grid @ first (just adding), can refactor get method accept bool indicating if data should loaded db first or not:

private void get(bool loaddatafirst) {    if(loaddatafirst) ctx.invoices.load();    collection = ctx.invoices.local; } 

now using get method without loading data first, collection still bound local cache (which should empty). after adding new items collection, local have items added automatically , save can call savechanges:

private void save() {    ctx.savechanges(); } 

the get method should used inside constructor replacing this.collection = new observablecollection<invoice>(); this:

public invoiceviewmodel() {    get(false); }