c# - Paggeable Datagrid ItemSource throws null exception -
i want create generic datagrid can paginate. when call constructor of datagrid_uc , pass 20 employees stores 20 employees in allobject observable collection. , filter out currentpageitems 5. upon setting datagrid.itemssource = currentpageitems throws null exception currentpageitems contain 5 items.
datagrid_uc.xaml
public partial class datagrid_uc : usercontrol { private observablecollection<object> _currentpageitems; public observablecollection<object> currentpageitems { { return _currentpageitems; } private set { if (_currentpageitems != value) { _currentpageitems = value; } } } // default entries per page number private int _pagesize = 5; public int pagesize { { return _pagesize; } set { if (_pagesize != value) { _pagesize = value; reset(); } } } public int totalpagesnumber { { if (allobjects != null && pagesize > 0) { return (allobjects.count - 1) / pagesize + 1; } return 0; } } private int _currentpagenumber = 1; public int currentpagenumber { { return _currentpagenumber; } protected set { if (_currentpagenumber != value) { _currentpagenumber = value; } } } protected observablecollection<object> allobjects { get; set; } public datagrid_uc() { initializecomponent(); datagrid.itemssource = currentpageitems; } public datagrid_uc(ienumerable<object> allobjects, int? entriesperpage = null) { allobjects = new observablecollection<object>(allobjects); if (entriesperpage != null) pagesize = (int)entriesperpage; setcurrentpageitems(); } #region public methods public void gotonextpage() { if (currentpagenumber != totalpagesnumber) { currentpagenumber++; setcurrentpageitems(); } } public void gotopreviouspage() { if (currentpagenumber > 1) { currentpagenumber--; setcurrentpageitems(); } } #endregion #region private methods public void setcurrentpageitems() { int upperlimit = currentpagenumber * pagesize; currentpageitems = new observablecollection<object>( allobjects.where(x => allobjects.indexof(x) > upperlimit - (pagesize + 1) && allobjects.indexof(x) < upperlimit)); datagrid.itemssource = currentpageitems; } private void reset() { currentpagenumber = 1; setcurrentpageitems(); } #endregion private void next_click(object sender, routedeventargs e) { if (currentpagenumber != totalpagesnumber) { currentpagenumber++; setcurrentpageitems(); } } private void previous_click(object sender, routedeventargs e) { if (currentpagenumber > 1) { currentpagenumber--; setcurrentpageitems(); } } } main window.xaml
public partial class mainwindow : window { public mainwindow() { initializecomponent(); list<employee> emp = new list<employee>(); (int = 0; < 20; i++) { employee e = new employee(); e.id = i; e.name = "test " + i; emp.add(e); } datagrid_uc d = new datagrid_uc(emp, 5); newcontentcontrol.content = d; } }
the datagrid member null because second constructor missing initializecomponent call, (among other things) initializes class members defined in xaml x:name.
so change constructor this:
public datagrid_uc(ienumerable<object> allobjects, int? entriesperpage = null) { initializecomponent(); allobjects = new observablecollection<object>(allobjects); ... } 
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