帮忙分析理解一下代码!谢谢!

请教高帮忙分析理解一下VBA代码.只有分析蓝色部分就可以了.谢谢!

第一段:

Option Compare Database
Option Explicit

Private Sub Form_Open(Cancel As Integer)
    Me.Caption = Me.OpenArgs
End Sub
Private Sub 预览_Click()
    If IsNull([开始日期]) Or IsNull([结束日期]) Then
        MsgBox "您必须输入开始日期和终止日期。"
        DoCmd.GoToControl "开始日期"
    Else
        If [开始日期] > [结束日期] Then
            MsgBox "截止日期必须大于开始日期。"
            DoCmd.GoToControl "开始日期"
        Else
            Me.Visible = False
        End If
    End If
End Sub

第二段:

Option Compare Database
Option Explicit

Private Sub Report_NoData(Cancel As Integer)
    MsgBox "没有此报表的数据。取消报表..."
    Cancel = -1
End Sub

Private Sub Report_Close()
    DoCmd.Close acForm, "报表日期范围"
End Sub

Private Sub Report_Open(Cancel As Integer)
    DoCmd.OpenForm "报表日期范围", , , , , acDialog, "ENT(DATE)"
    If Not IsLoaded("报表日期范围") Then
        Cancel = True
    End If
End Sub

第三段:

Option Compare Database
Option Explicit

Function IsLoaded(ByVal strFormName As String) As Boolean
 ' 如果指定窗体在窗体视图或数据表视图中打开，返回 True。
   
    Const conObjStateClosed = 0
    Const conDesignView = 0
   
    If SysCmd(acSysCmdGetObjectState, acForm, strFormName) <> conObjStateClosed Then
        If Forms(strFormName).CurrentView <> conDesignView Then
            IsLoaded = True
        End If
    End If
   
End Function