如何把一個 data entity 轉換成ObservableCollection

Question

請問各位先進,比較以下兩段簡單的程序片段

下列的做法是OK的,DataGrid1 裏有資料出現,

   LoadOperation<Product> loadOP = DS.Load(DS.GetProductQuery());
   dataGrid1.ItemsSource = loadOP.Entities;                         

可是以下的做法卻不行, dataGrid1 裏沒有資料 ?? 為什麼 ObservableCollection<Product> 裏沒有資料;

    LoadOperation<Product> loadOP = DS.Load(DS.GetProductQuery());
    ObservableCollection<Product> _products = new ObservableCollection<Product>(loadOP.Entities);

    dataGrid1.ItemsSource = _products;

上述的問題,我想不出來,故求教各位先進.

           

Answer 1

_products有数据吗，

Answer 2

你好 joseph9406，

LoadOperation 是異步的，dataGrid1裏面是不會有資料的。

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Mark Yu - MSFT
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Answer 3

主要是下列的陳述有問題,

ObservableCollection<Product> _products = new ObservableCollection<Product>(loadOP.Entities);

loadOP.Entities 裏是有資料的,我在"偵錯"下,是可以看見裏頭有資料,

可是它就是填不進 "_products" 裏 (為什麼 ??)

它也不是異步的問題,因為 dataGrid1.ItemsSource = loadOP.Entities;  是OK的,這是一個很單純的式子.

Answer 4

你好，

》》 LoadOperation<Product> loadOP = DS.Load(DS.GetProductQuery());

這裏的LoadOperation代表一個異步操作，後面的dataGrid1.ItemsSource獲取的此異步操作的結果

》》loadOP.Entities 裏是有資料的

loadOP.Entities裏的資料是通過LoadOperation這個異步操作后加載進來的，你可以看一下以下的截圖， loadOP.Entites是空的

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Mark Yu - MSFT
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Answer 5

另外再作一點補充，你可以添加以下代碼測試一下：

 LoadOperation<Users> loadOp = this.ds2.Load(this.ds2.GetUsersQuery());
            
            dataGrid1.ItemsSource = loadOp.Entities;
            List<Users> temp = loadOp.Entities.ToList<Users>();
            foreach(Users s in temp)
            {
                //MessageBox.Show(s.ToString());
                MessageBox.Show(s.AuthType.ToString()+s.EntityActions.ToString()+s.EntityConflict.ToString()+s.EntityState.ToString());
            }

在這些代碼上設置斷點，你可以發現當你設置了dataGrid1.ItemsSource = loadOp.Entities，程序執行這一步以及後面的foreach完畢后，程序才會執行到Entity里的set。

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Mark Yu - MSFT
MSDN Community Support | Feedback to us
Develop and promote your apps in Windows Store
Please remember to mark the replies as answers if they help and unmark them if they provide no help.

Answer 6

{...

DS.Load(DS.GetProductQuery(),loadCallBack,null);