[英]Initialize of a Class as variable in c#
我聽不懂這段代碼。 為什么我需要將一個類初始化為變量,例如“ private InvoiceMaster _invoiceMaster”和“ InvoiceMaster im = new InvoiceMaster()”。 請詳細幫助我。 我需要非常清楚地了解。
namespace AHS.Invoice.UI
{
public partial class ReRouteDetail : BasePage
{
#region Declaration
private InvoiceMaster _invoiceMaster;
DataSet _ds = new DataSet();
InvoiceMasterCollection _invoiceMasterCollection = new InvoiceMasterCollection();
#endregion
#region Page Events
protected void Page_Load(object sender, EventArgs e)
{
}
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
if (!IsPostBack)
{
}
this.LoadColumns();
this.LoadGridData();
}
#endregion
#region Methods
private void LoadGridData()
{
if (base.CurrentScreen.ID == 3780)
{
_ds = new InvoiceMasterCollection().LoadReRouteData();
gc.GridDataSource = _ds;
gc.GridDataBind();
}
else if (base.CurrentScreen.ID == 3781)
{
_ds = new InvoiceMasterCollection().LoadReRouteFromServiceApproverData();
gc.GridDataSource = _ds;
gc.GridDataBind();
}
else if (base.CurrentScreen.ID == 3782)
{
_ds = new InvoiceMasterCollection().LoadReRouteFromServiceConfirmationData();
gc.GridDataSource = _ds;
gc.GridDataBind();
}
}
#endregion
#region Events
protected void gc_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
DropDownList ddlStatus = e.Row.Cells[7].FindControl("ddlStatus") as DropDownList;
ddlStatus.CssClass = "ReRouteddlStatus";
if (base.CurrentScreen.ID == 3780)
{
DataSet reRouteDataSet = new InvoiceMasterCollection().LoadStatus(Convert.ToInt32(e.Row.Cells[4].Text));
ddlStatus.DataTextField = "Description";
ddlStatus.DataValueField = "ID";
ddlStatus.DataSource = reRouteDataSet;
ddlStatus.DataBind();
}
if (base.CurrentScreen.ID == 3781 || base.CurrentScreen.ID == 3782)
{
ddlStatus.Enabled = false;
}
System.Web.UI.WebControls.Button btnReRoute = e.Row.Cells[8].FindControl("btnReRoute") as System.Web.UI.WebControls.Button;
btnReRoute.CssClass = "btnBackToReRoute";
//Button btnReRoute = e.Row.Cells[8].FindControl("btnReRoute") as Button;
btnReRoute.CommandName = "ReRoute";
btnReRoute.CommandArgument = e.Row.Cells[0].Text;
e.Row.Cells[8].Controls.Add(btnReRoute);
}
}
protected void gc_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "ReRoute")
{
int masterID = Convert.ToInt32(e.CommandArgument);
Button button = null;
foreach (GridViewRow rows in gc.GridRows)
{
InvoiceMaster im = new InvoiceMaster();
im.ID = masterID;
// this.LoadGridData();
_invoiceMaster = new InvoiceMaster();
_invoiceMaster = im.GetData();
int id = Convert.ToInt32(rows.Cells[0].Text);
if (id == masterID)
{
button = rows.FindControl("btnReRoute") as Button;
DropDownList ddlStatus(DropDownList)rows.Cells[6].FindControl("ddlStatus");
if (base.CurrentScreen.ID == 3780)
{
_invoiceMaster.StatusID = Convert.ToInt32(ddlStatus.SelectedItem.Value);
}
if (base.CurrentScreen.ID == 3781)
{
_invoiceMaster.StatusID = 13;
}
if (base.CurrentScreen.ID == 3782)
{
_invoiceMaster.StatusID = 11;
}
_invoiceMaster.Save();
break;
}
}
LoadColumns();
LoadGridData();
base.ShowClientMessage("Invoice Backed Successfully.");
}
}
#endregion
}
}
當您編寫此行時:
private InvoiceMaster _invoiceMaster;
您只是在定義InvoiceMaster
類型的類的私有成員。 然而,在這一點上,引用沒有指向任何東西(“值”為null
)。
在這一行:
InvoiceMaster im = new InvoiceMaster();
您還將創建該類的私有成員(c#中的默認成員是private
),這一次您將向該引用分配正在創建的新對象。
以下各行將無法編譯,並且必須在函數范圍內:
im.ID = masterID;
_invoiceMaster = new InvoiceMaster();
_invoiceMaster = im.GetData();
我建議您閱讀其中的許多教程之一,以更好地了解數據類型,變量和范圍
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