我是Xamarin的新手，我正试图从自己身上刷新MainActivity。我阅读了很多关于此的论坛，但我仍然无法找到任何解决方案。我的问题是我需要从另一种方法中刷新，而不是在onCreate()方法中。
我的MainActivity是listview，我想重新加载整个活动以刷新列表视图。我需要重新加载整个活动，因为在我的情况下我无法使用NotifyDataSetChanged()，因为我对listview所做的更改不在onCreate()方法内，而不在新活动也没有。我有一个CAB菜单，用户可以从中选择从列表视图中删除所选的注释。我在NotifyDataSetChanged()方法中使用onResume()方法，当我在另一项活动中对listview进行更改但它无法正常工作时，它工作正常当我从当前活动中创建它们时，因为那时没有调用onResume()方法。
我试过这样做：
Intent refresh = new Intent(this,typeof(MainActivity));
refresh.AddFlags(ActivityFlags.NoAnimation);
Finish();
StartActivity(refresh);
但它已经在第一行给了我NullPointerException ..我认为例外是＃34;这个＆＃34;。所以我尝试了不同的方式：而不是使用＆＃34;这个＆＃34;我在Intent refresh = new Intent(context ,typeof(MainActivity));方法中使用 - onCreate() where context = this。但是通过这种方式它仍然给了我一个NullPointerException，但这一次在行 - StartActivity(refresh) ..
提前致谢！ ：）
答案 0 :(得分：0)
NotifyDataSetChanged()绝对可以在OnCreate / OnResume之外的其他方式使用
如果您想使用NotifyDataSetChanged()，则需要更改ListAdapter中与ListView相关联的项目。
像这样的东西
namespace MyNamespace
{
[Activity]
public MyActivity : Activity
{
private ArrayAdapter<string> myAdapter = null;
public override void OnCreate(Bundle savedInstanceState)
{
myAdapter = new ArrayAdapter<string>(); //or whatever type your adapter is.
myListView.Adapter = myAdapter;
}
private void UpdateList()
{
//Delete item
myAdapter.Remove(item);
//Insert item
myAdapter.Insert(item, 0); //0 = position for new item
//Add item
myAdapter.Add(item);
myAdapter.NotifyDataSetChanged();
}
}
}
答案 1 :(得分：0)
这是代码：
public List<DeliveryNoteInfo> _lstNoteInfo = new List<DeliveryNoteInfo>();
public ObjectToSerialize objectToSerialize;
public Serializer serializer;
private ListView objListItem;
private MonoBaseAdapter2 myAdapter = null;
static AlertDialog levelDialog;
static string[] items;
static Context context2;
protected override void OnCreate (Bundle SavedInstanceState)
{
base.OnCreate (SavedInstanceState);
// Set our view from the "main" layout resource
SetContentView (Resource.Layout.Main);
// Get our UI controls from the loaded layout
Button addButton = FindViewById<Button>(Resource.Id.AddButton);
addButton.Click += delegate {
StartActivity (typeof(AddActivity));
};
Button sortButton = FindViewById<Button>(Resource.Id.SortButton);
sortButton.Click += delegate {
ShowSortDialog(_lstNoteInfo);
};
Button exitButton = FindViewById<Button>(Resource.Id.ExitButton);
exitButton.Click += delegate {
Finish();
};
context2 = this;
// Loading the already saved notes from external file
objectToSerialize = new ObjectToSerialize();
serializer = new Serializer ();
var path = System.Environment.GetFolderPath(System.Environment.SpecialFolder.ApplicationData);
if (System.IO.File.Exists (path + "outputFile.txt")) {
deserialize ();
}
//Displaying the Notes in a custom made ListView
objListItem = FindViewById<ListView> (Resource.Id.listView1);
myAdapter = new MonoBaseAdapter2 (this, _lstNoteInfo);
objListItem.Adapter = myAdapter;
objListItem.FastScrollEnabled = true;
objListItem.ChoiceMode = (ChoiceMode)AbsListViewChoiceMode.MultipleModal;
objListItem.SetMultiChoiceModeListener (new CabMenu(this,this,objListItem));
objListItem.ItemClick += delegate(object sender, AdapterView.ItemClickEventArgs e) {
var itemClicked = new Intent(this,typeof(InfoActivity));
itemClicked.PutExtra("File name",_lstNoteInfo[e.Position].ImageID);
itemClicked.PutExtra("Date",_lstNoteInfo[e.Position].Date);
itemClicked.PutExtra("Type",_lstNoteInfo[e.Position].Type);
itemClicked.PutExtra("Name",_lstNoteInfo[e.Position].Name);
itemClicked.PutExtra("Supplier",_lstNoteInfo[e.Position].Supplier);
itemClicked.PutExtra("Amount",_lstNoteInfo[e.Position].Amount);
itemClicked.PutExtra("Info",_lstNoteInfo[e.Position].AddInfo);
StartActivity (itemClicked);
};
}
protected override void OnResume ()
{
base.OnResume ();
var lstNoteInfo = new List<DeliveryNoteInfo>();
var path = System.Environment.GetFolderPath(System.Environment.SpecialFolder.ApplicationData);
if (System.IO.File.Exists (path + "outputFile.txt")) {
objectToSerialize = serializer.DeSerializeObject ("outputFile.txt");
lstNoteInfo = objectToSerialize.DeliveryNoteInfo;
}
_lstNoteInfo.Clear ();
_lstNoteInfo.AddRange (lstNoteInfo);
((MonoBaseAdapter2)objListItem.Adapter).NotifyDataSetChanged ();
objListItem.Invalidate ();
((MonoBaseAdapter2)objListItem.Adapter).NotifyDataSetInvalidated ();
}
public void makeNote (String fileName, String finalDate, String type,String noteName, String amount, String supplier, String addInfo)
{
_lstNoteInfo.Add (new DeliveryNoteInfo (){ ImageID = fileName, Date = finalDate,Type = type, Name = noteName, Amount = amount, Supplier = supplier, AddInfo = addInfo});
objectToSerialize.DeliveryNoteInfo = _lstNoteInfo;
serializer.SerializeObject("outputFile.txt", objectToSerialize);
Console.WriteLine ("Name: " + noteName);
Console.WriteLine ("Amount: " + amount);
}
public void RefreshAfterDelete(List<DeliveryNoteInfo> updatedList)
{
_lstNoteInfo.Clear ();
_lstNoteInfo.AddRange (updatedList);
objectToSerialize.DeliveryNoteInfo = _lstNoteInfo;
serializer.SerializeObject("outputFile.txt", objectToSerialize);
UpdateList ();
}
public void PrintCollection<T>(IEnumerable<T> col)
{
foreach(var item in col)
System.Console.WriteLine("ITEM");
}
void deserialize ()
{
objectToSerialize = serializer.DeSerializeObject ("outputFile.txt");
_lstNoteInfo = objectToSerialize.DeliveryNoteInfo;
}
void deserialize(List<DeliveryNoteInfo> list)
{
objectToSerialize = serializer.DeSerializeObject ("outputFile.txt");
list = objectToSerialize.DeliveryNoteInfo;
}
void serialize (List<DeliveryNoteInfo> list)
{
objectToSerialize.DeliveryNoteInfo = list;
serializer.SerializeObject("outputFile.txt", objectToSerialize);
}
private void ShowSortDialog(List<DeliveryNoteInfo> updatedList)
{
// Strings to Show In Dialog with Radio Buttons
items = new string[]{" Date "," Name "," Type of delivery "," Supplier "};
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.SetTitle("Sort by ..");
builder.SetSingleChoiceItems(items, -1, onClick);
levelDialog = builder.Create();
levelDialog.Show();
}
public void onClick(object sender, DialogClickEventArgs e) {
var item = (int) e.Which;
List<DeliveryNoteInfo> list = new List<DeliveryNoteInfo> ();
switch(item)
{
case 0:
// Your code when first option seletced
Console.WriteLine ("Sorting by date..");
break;
case 1:
// Sorting by name
objectToSerialize = serializer.DeSerializeObject ("outputFile.txt");
list = objectToSerialize.DeliveryNoteInfo;
List<DeliveryNoteInfo> SortedList = list.OrderBy (o => o.Name).ToList ();
RefreshAfterDelete (SortedList);
Console.WriteLine ("Sorting by name..");
break;
case 2:
// Your code when 3rd option seletced
Console.WriteLine ("Sorting by type of delivery..");
break;
case 3:
// Your code when 4th option seletced
Console.WriteLine ("Sorting by supplier ..");
break;
}
levelDialog.Dismiss();
}
private void ListClicked (object sender, DialogClickEventArgs e)
{
var builder = new AlertDialog.Builder (this);
builder.SetMessage (string.Format ("You selected: {0} , {1}", (int)e.Which, items [(int)e.Which]));
builder.Show ();
}
private void UpdateList()
{
myAdapter.NotifyDataSetChanged();
}
}