WeakReference.Target 屬性

定義

命名空間:

System

組件:

System.Runtime.dll

來源:

WeakReference.cs

取得或設定目前 WeakReference 物件所參考的物件 (目標)。

public:
 virtual property System::Object ^ Target { System::Object ^ get(); void set(System::Object ^ value); };

public virtual object? Target { get; set; }

member this.Target : obj with get, set

Public Overridable Property Target As Object

屬性值

Object

如果目前 WeakReference 物件所參考的物件已進行記憶體回收，則為 null；否則為目前 WeakReference 物件所參考物件的參考。

例外狀況

InvalidOperationException

目標物件的參考無效。 如果值為 null 參考或已在集合作業期間完成物件，則可以在設定這個屬性時擲回這個例外狀況。

範例

下列範例會嘗試從具有弱式參考之物件的快取中取得 物件。 如果物件已回收以進行垃圾收集，就會產生新的 物件。 此範例是針對 類別提供的較大範例的 WeakReference 一部分。

Data d = _cache[index].Target as Data;
if (d == null) {
    // If the object was reclaimed, generate a new one.
    Console.WriteLine("Regenerate object at {0}: Yes", index);
    d = new Data(index);
    _cache[index].Target = d;
    regenCount++;
}
else {
    // Object was obtained with the weak reference.
    Console.WriteLine("Regenerate object at {0}: No", index);
}

return d;

match _cache[index].Target with
| :? Data as d->
    // Object was obtained with the weak reference.
    printfn $"Regenerate object at {index}: No"
    d
| _ ->
    // If the object was reclaimed, generate a new one.
    printfn $"Regenerate object at {index}: Yes"
    let d = Data index
    _cache[index].Target <- d
    regenCount <- regenCount + 1
    d

 Dim d As Data = TryCast(_cache(index).Target, Data)
 ' If the object was reclaimed, generate a new one.
 If d Is Nothing Then 
     Console.WriteLine("Regenerate object at {0}: Yes", index)
     d = New Data(index)
     _cache(index).Target = d
     regenCount += 1
Else 
     ' Object was obtained with the weak reference.
     Console.WriteLine("Regenerate object at {0}: No", index.ToString())
 End If 
 Return d

備註

將此屬性設定為目標物件之後，請確定物件沒有其他強式參考;否則，將不會收集它。

另請參閱

• Object
• GC
• 弱式參考