Class

WeakRef

Description

Allows you to retain a reference to an object without requiring it to stay alive.

Properties

Name	Type	Read-Only	Shared
Value	Object	✓

Methods

Name	Parameters	Returns	Shared
Constructor	obj As Object

Property descriptions

WeakRef.Value

Value As Object

Returns the target object or Nil if the target no longer exists.

This property is read-only.

Method descriptions

WeakRef.Constructor

Constructor(obj as Object)

Note

Constructors are special methods called when you create an object with the New keyword and pass in the parameters above.

Creates a WeakRef instance.

The target object that you want to retain a reference to after it has been destroyed.

This example creates a weak reference to a SQLiteDatabase object. The property "db As SQLiteDatabase" is a property on the App object.

Var dbRef As WeakRef

' Create Database Object
DB = New SQLiteDatabase
dbRef = New WeakRef(DB)
' Set Database File
DB.DatabaseFile = New FolderItem("MyDatabase.sqlite")

Notes

WeakRef is useful when you want to find out when an object (such as a database or TCP/IP connection) is still in use somewhere in the application. The reference returned by WeakRef goes to Nil as soon as there are no longer any references to the object. This is the signal that you can do any necessary cleanup work.

When the object is destroyed, the WeakRef's value will change to Nil after all ordinary references have been released and the object has been destroyed. Otherwise, the Value property returns the target object.

Sample code

This code declares an instance of a FolderItem that will go out of scope and have its reference counter decreased. A weak reference is assigned to the FolderItem instance. While the instance is available, its name is displayed. When the instance is removed from memory, the weak reference value become Nil, so you now know there are no more references to it:

Var ref As WeakRef
If True Then
  Var f As New FolderItem
  f.Name = "TestFile.txt"
  ref = New WeakRef(f)
  If ref.Value <> Nil Then
    MessageBox(FolderItem(ref.Value).Name) ' This is shown
  Else
    MessageBox("f is Nil.")
  End If
End If

If ref.Value <> Nil Then
  MessageBox(FolderItem(ref.Value).Name)
Else
  MessageBox("f is Nil.") ' This is shown
End If

Compatibility

All project types on all supported operating systems.