In my application I have a ListView with "sections". For each item, I added a letter, but they are visible only for the first word beginning with that letter. It works fine, but if I scroll down in my ListView, the order changes, that means the letter is going to next item.
Example:
A
--
- Alligator
- Ant
- Antelope
- Ape
But when I scroll down, the following happens:
- Aligator
A
--
- Ant
- Antelope
- Ape
Function that adds the letter I have implemented in GetView()
How can I solve this problem?
I read that ListView is refreshing while scrolling, how can I disable refreshing? Or is there the other way to solve this?
protected string old_char = "";
public override View GetView(int position, View convertView, ViewGroup parent)
{
var item = sw_items [position];
View view;
convertView = null;
view = (convertView ??
this.context.LayoutInflater.Inflate (Resource.Layout.ItemLayout,
parent,
false)) as LinearLayout;
var txtTitle = view.FindViewById<TextView> (Resource.Id.txtTitle);
txtTitle.SetText (sw_items [position].name, TextView.BufferType.Normal);
var alfabet = view.FindViewById<TextView> (Resource.Id.alfabet);
var linAlfabet = view.FindViewById<LinearLayout> (Resource.Id.Lin_Alfabet);
if (convertView == null) {
string cnv_char = item.name [0].ToString ().ToUpper ();
alfabet.Text = cnv_char;
if (cnv_char != old_char) {
alfabet.Visibility = ViewStates.Visible;
linAlfabet.Visibility = ViewStates.Visible;
} else {
alfabet.Visibility = ViewStates.Gone;
linAlfabet.Visibility = ViewStates.Gone;
}
//saving previous char
old_char = cnv_char;
}
return view;
}
}
What am I doing wrong?
Revised
First, the basic scheme for getView() implementations is as follows.
if (convertView == null) {
// the system does not want me to recycle a view object, so create a new one
LayoutInflater inflater = (LayyoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.your_layout_file, parent, false);
}
// here, set up the convertView object, no matter whether it was recycled or not
...
return convertView;
Given the code snippet you posted, all you probably have to do is: 1. remove the convertVire = null; statement which Yatin suggested and 2. remove the surrounding if (convertView == null) { including closing } around the string cnv_char... old_char = cnv_char block. Make sure to set everything properly for convertView, because it is not guaranteed to be a fresh object.
Second, your code is relying on getView() being called in a particular order, which is not the case. Currently, you're relying on old_char being set to the starting letter of the last item (in the order in which they appear in the list). This is not guiaranteed.
I suggest you use the position argument to access the previous entry of the list (except for the first, of course) and check for a difference, showing the starting letter of the current item if there is no predecessor or if it starts with a different letter.
ListView reuses views in stack to replace the view which is scrolled up to place it again at the bottom
try adding the following statement in the code before as :-
convertView=null;
before it checks for
if(convertView==null);
Related
I'm using Load/Save layout similar way described on CodeProject. Catching LayoutSerializationCallback event and trying to find the corresponding viewModel for LayoutItem
private void LayoutSerializer_LayoutSerializationCallback(object sender, LayoutSerializationCallbackEventArgs e)
{
// This can happen if the previous session was loading a file
// but was unable to initialize the view ...
if (string.IsNullOrWhiteSpace(e.Model.ContentId) || (e.Content = ReloadItem(e.Model)) == null)
{
e.Cancel = true;
return;
}
}
private object ReloadItem(object item)
{
object ret = null;
switch (item)
{
case LayoutAnchorable anchorable:
//list of tools windows
ret = Manager.Tools.FirstOrDefault(i => i.ContentId == anchorable.ContentId);
if(ret == null && anchorable.ContentId.StartsWith(MapPanel.MapPanelPrefix))
{
MapPanels.Add(anchorable);
}
break;
case LayoutDocument document:
// list of restored documents
ret = Manager.Documents.FirstOrDefault(i => i.ContentId == document.ContentId);
break;
default:
throw new NotImplementedException("Not implemented type of AD item ");
}
return ret;
}
This works fine when I have all ViewModels available when deserializing/restoring layout.
But I'm thinking about something like delayed layout restore. In my case, I have some documents and some panels available at the start. But there can be some panels (call them MapPanel) that are loaded later (viewModels are loaded somewhere in future). And I can't figure out, how to restore layout for these panels.
For this case, I have List MapPanels to store anchorable that are loaded at avalondock layout load and trying to restore them in BeforeInsertAnchorable in ILayoutUpdateStrategy. But when I debug it, stored LayoutAnchorable has different parents that stored one. So I assume that after canceling (e.Cancel = true) in LayoutSerializationCallback somehow modifies not restored anchorable.
public bool BeforeInsertAnchorable(LayoutRoot layout, LayoutAnchorable anchorableToShow, ILayoutContainer destinationContainer)
{
if (anchorableToShow.Content is ToolPanel tool)
{
if(tool is MapPanel)
{
anchorableToShow = LayoutSaveLoadUtil.Instance.MapPanels.FirstOrDefault(mp => mp.ContentId == anchorableToShow.ContentId);
}
var destPane = destinationContainer as LayoutAnchorablePane;
if (destinationContainer != null && destinationContainer.FindParent<LayoutFloatingWindow>() != null)
return false;
var dockLeftPane = layout.Descendents().OfType<LayoutAnchorablePane>().FirstOrDefault(d => d.Name == tool.PreferredLocation + "Pane");
if (dockLeftPane != null)
{
dockLeftPane.Children.Add(anchorableToShow);
return true;
}
return false;
}
return false;
}
So I'm curious what is the right approach to achieve this. I was also thinking about restoring layout (again) after MapPanel is loaded, but I don't know how to skip all other LayoutItems. So is there any possibility of how to restore a single Anchorable position, floating parent, docking, size, etc...?
So i probably figured out solution.
I have some panels (call them MapPanel) and theyr content isnt loaded when layout is restored from XML. In my case i have app, that has some documents and tabs, and in aditional, user can load aditional data to show maps.
And i needed to restore layout of this maps when user load them. (click button, selec where to load maps etc)
I have static class called LayoutSaveLoadUtil (as described on codeproject) when i have aditional list MapPanelsStorage of type LayoutAnchorable. To this list i store all layouts that missing content on layout restore and ContentId has specific prefix. This tells me that is MapPanel. Then i create a dummy content, assign it to this panel and set its visibility to false (so panel is invisible)
(this is called in layoutSerializationCallback)
private object ReloadItem(object item)
{
object ret = null;
switch (item)
{
case LayoutAnchorable anchorable:
//list of tools windows
ret = Manager.Tools.FirstOrDefault(i => i.ContentId == anchorable.ContentId);
if(ret == null && anchorable.ContentId.StartsWith(MapPanel.MapPanelPrefix))
{
//when layoutAnchorable is MapPanel (has MapPanel prefix) and its content is loaded yet
//store its layout into list to restore it later (when content is loaded)
MapPanelsStorage.Add(anchorable);
//Set anchorable visibility to false
anchorable.IsVisible = false;
//return dummy model for avalondock layout serialization
ret = new EmptyMapViewModel();
}
break;
case LayoutDocument document:
// list of restored documents
ret = Manager.Documents.FirstOrDefault(i => i.ContentId == document.ContentId);
break;
default:
throw new NotImplementedException("Not implemented type of AD item ");
}
return ret;
}
Then in BeforeInsertAnchorable (called when new panel is added into layout) i check if panel content is MapPanel, look for stored layout, try to find parent (LayoutAnchorablePane/LayoutDocumentPane) and then add it instead of DummyHidden panel, and just remove it from storage.
//hacky hacky to restore map panel layout when map is opened after layout is loaded
//in layout deserialization, deserialize layout for MapPanels that hasnt DataModels yet with DummyModel to preserve their layout
if (anchorableToShow.Content is MapPanel mappanel)
{
var storedMapsLayout = LayoutSaveLoadUtil.Instance.MapPanelsStorage;
//check if Map panel has stored layout from previous layout deserialization
var matchingAnchorable = storedMapsLayout.FirstOrDefault(m => m.ContentId == mappanel.ContentId);
if (matchingAnchorable != null)
{
//make preserved layout visible, so its parent and etc is restored. Without this, correct parent LayoutGroup isnt found
matchingAnchorable.IsVisible = true;
LayoutAnchorablePane matchingAnchorablePane;
LayoutDocumentPane matchingDocumentPane;
//find parent layoutGroup. This can be LayoutAnchorablePane or LayoutDocumentPane
if ((matchingAnchorablePane = matchingAnchorable.FindParent<LayoutAnchorablePane>()) != null)
{
//add new panel into layoutGroup with correct layout
matchingAnchorablePane.Children.Add(anchorableToShow);
//remove old dummy panel
matchingAnchorablePane.RemoveChild(matchingAnchorable);
//remove restored layout from storage
storedMapsLayout.Remove(matchingAnchorable);
return true;
}
else if ((matchingDocumentPane = matchingAnchorable.FindParent<LayoutDocumentPane>()) != null)
{
//add new panel into layoutGroup with correct layout
matchingDocumentPane.Children.Add(anchorableToShow);
//remove old dummy panel
matchingDocumentPane.RemoveChild(matchingAnchorable);
//remove restored layout from storage
storedMapsLayout.Remove(matchingAnchorable);
return true;
}
else
{
matchingAnchorable.IsVisible = false;
}
}
}
I'm using iCarousel by #Nick Lookwood to load a scrollable list of "flashcards".
Each View of the iCarousel control is one flashcard. By design, I require that when a user taps the flashcard (view), the flashcard flips to reveal the behind. Before using iCarousel, I was making two separate controls, one for front and one for back, and then using UIView.Transition (with a nice Flip From Top animation) to go from front to back when a Tap was detected, or the other way round.
Adding a UITapGestureRecognizer to my View is leading to weird artifacts and not functioning as expected (overlapping controls, the next one instead of the current one flipping, no animation, etc.) and I need a different approach. I could conveniently use the Selected event in the iCarousel Delegate instead of a Tap Gesture Recognizer, but what do I do there exactly?
In essence, I would like to replace the specific view which was tapped with another but I feel this is conflicting with the whole reusable views idea. Is there nothing I can do? (Once the view is out of the screen, I am fine with it being "flipped forward" again.)
Thanks!
p
P.S. I'm using C# and Xamarin.iOS, but I can understand Obj-C and Swift code fairly well, so any help will be appreciated.
There are lots of example for iCarausal. I assume you are using this :
iCarausal
and specifically folder name "Basic iOS Example"
How about the below changes in delegate methods:
- (UIView *)carousel:(iCarousel *)carousel viewForItemAtIndex:(NSInteger)index reusingView:(UIView *)view
{
UILabel *label = nil;
//create new view if no view is available for recycling
if (view == nil)
{
//don't do anything specific to the index within
//this `if (view == nil) {...}` statement because the view will be
//recycled and used with other index values later
view = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 200.0f, 200.0f)];
((UIImageView *)view).image = [UIImage imageNamed:#"page.png"];
view.contentMode = UIViewContentModeCenter;
//back view i have just added this apart from it there is no change made by me in this method
UIView *backView = [[UIView alloc] initWithFrame:view.bounds];
backView.tag = 2;
[backView setBackgroundColor:[UIColor redColor]];
[view addSubview:backView];
[backView setHidden:YES];
//back view
label = [[UILabel alloc] initWithFrame:view.bounds];
label.backgroundColor = [UIColor clearColor];
label.textAlignment = NSTextAlignmentCenter;
label.font = [label.font fontWithSize:50];
label.tag = 1;
[view addSubview:label];
}
else
{
//get a reference to the label in the recycled view
label = (UILabel *)[view viewWithTag:1];
}
//set item label
//remember to always set any properties of your carousel item
//views outside of the `if (view == nil) {...}` check otherwise
//you'll get weird issues with carousel item content appearing
//in the wrong place in the carousel
label.text = [_items[index] stringValue];
return view;
}
and implementing didSelect delegate as below:
- (void)carousel:(iCarousel *)carousel didSelectItemAtIndex:(NSInteger)index{
UIView *frontview = [carousel itemViewAtIndex:index];
UIView *backView = [frontview viewWithTag:2];
BOOL isInFront = NO;
if (backView.hidden == NO) {
isInFront = YES;
}
[UIView transitionWithView: isInFront ? backView : frontview
duration:1.0
options:UIViewAnimationOptionTransitionFlipFromLeft
animations:^{
[backView setHidden:isInFront];
}
completion:nil];
}
You should write your code more structured, it was an example to show you that you can acheive what you want with iCarausal.
I'm trying to create an expendable list with text as well as an ImageView. This is how I'm currently doing this: There's one parent xaml and two children xaml (a ChildText.xaml and a ChildImage.xaml). I want one of the parent items to contain an image. I used following code in my adapter:
public override View GetChildView (int groupPosition, int childPosition, bool isLastChild, View convertView, ViewGroup parent) {
var item = _dictGroup [_lstGroupID [groupPosition]] [childPosition];
if(item.Contains("ichart")) {
if (convertView == null)
convertView = _activity.LayoutInflater.Inflate (Resource.Layout.ListControl_ImageChild, null);
var imageView = convertView.FindViewById<ImageView>(Resource.Id.image);
var imageBitmap = GetImageBitmapFromUrl (item);
imageView.SetImageBitmap (imageBitmap); //X
} else {
string[] data = item.Split ('_');
if (convertView == null)
convertView = _activity.LayoutInflater.Inflate (Resource.Layout.ListControl_Child, null);
var titleBox = convertView.FindViewById<TextView> (Resource.Id.titleSmall);
var textBox = convertView.FindViewById<TextView> (Resource.Id.txtSmall);
titleBox.SetText (data[0], TextView.BufferType.Normal);
textBox.SetText (data[1], TextView.BufferType.Normal);
}
return convertView;
}
So if the string contains ichart, it should create an ImageView. This works, but when I try to click open another tab (containing text), I get a nullpointer exception on the line with the X saying imageView is null. Why is it entering that if?
Can anyone tell me what I'm doing wrong?
Thanks in advance
First of all we have to make an array of images & parent names we want to put in expandable list view. Then call these arrays by using array adapter class.
you have to put the first variable manually in .xml file after that array adapter set all images & textview as per array you made.
I have a listview with a checkbox on each row and I need to make it so that if the user exits the app and later comes back to that liistview the same items remain checked, I have succesfully saved the checked items, but If I try to recheck them in the getview() method the list starts to lag, and random checkboxes start getting checked.
Below is my code that rechecks the boxes
using (VehicleFeaturesDB vfdb = new VehicleFeaturesDB())
{
selectedfeatures = vfdb.GetSelectedFeatures(Selector.vehicleId);
if (listOfSelectedFeatures != null)
{
foreach (Features f in listOfSelectedFeatures)
{
if (feature.FeatureID == f.FeatureID)
{
CheckBox.Checked = true;
}
}
}
}
Tha
If that using block is in GetView(), you're connecting to the database and pulling the list of features every time a new item is displayed. That's why you're seeing the lag.
You're also not setting Checked to false if the feature is not in the list, so when you reuse the convertview the checkbox may already be checked. That's why you're seeing the random boxes checked.
I would probably get the selected features in your adapter's constructor, then reference that list in your GetView(). Something like this should work for you.
public class MyAdapter...
{
private IEnumerable<SelectedFeature> selectedFeatures;
public MyAdapter()
{
...your code...
using (VehicleFeaturesDB vfdb = new VehicleFeaturesDB())
{
selectedfeatures = vfdb.GetSelectedFeatures(Selector.vehicleId);
}
}
public override View GetView(int pos, View convertView, ViewGroup parent)
{
...your code...
CheckBox.Checked = selectedFeatures.Any(sf => sf.FeatureID == feature.FeatureID);
}
I am trying to get the text value of a "cell" inside of a GridView that is set as the view of a ListView. I do not want to get the SelectedItem of the ListView as that just returns my entire View Model (but not which property the cell refers to).
I am able to get the text value by responding to direct mouse events (up down or whatever) and if the value is a textblock, obviously I can use the text. This works great and as of right now this is my only solution, although its currently limited.
I would like to take it a step further and be able to click anywhere with in the cell area, navigate around to find the appropriate textblock and then use that value. I have tried a half million ways to do this but what seems logical doesn't seem to quite work out like it should.
Setup:
I have a dynamic GridView that creates its own columns and bindings based on data models that I pass to it. I am using a programmatic cell template (shown below) to have individual control over the cells, particularly so I can add a "border" to it making it actually separate out each cell. I have named the objects so I can access them easier when I'm navigating around the VisualTree.
Here is the Template Code. (Note that the content presenter originally was a textblock itself, but this was changed for later flexibility)
private DataTemplate GetCellTemplate(string bindingName)
{
StringBuilder builder = new StringBuilder();
builder.Append("<DataTemplate ");
builder.Append("xmlns='http://schemas.microsoft.com/winfx/");
builder.Append("2006/xaml/presentation' ");
builder.Append("xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' ");
builder.Append("xmlns:local = 'clr-namespace:XXXXXXXX");
builder.Append(";assembly=XXXXXXXXX'>");
builder.Append("<Border Name=\"border\" BorderThickness=\"1,0,0,0\" BorderBrush=\"Gray\" Margin=\"-6,-3,-6,-3\">");
builder.Append("<Grid Margin=\"6,3,6,3\">");
builder.Append("<ContentPresenter Name=\"content\" HorizontalAlignment=\"Stretch\" Content=\"{Binding ");
builder.Append(string.Format("{0}", bindingName));
builder.Append("}\"/>");
builder.Append("</Grid>");
builder.Append("</Border>");
builder.Append("</DataTemplate>");
DataTemplate cellTemplate= (DataTemplate)XamlReader.Parse(builder.ToString());
return cellTemplate;
}
What I have Tried:
The logical approach for me was to react to a Mouse event. From the object that had the mouse event I would do either
A. Look at its children to find a textblock, or
B. Get its parent then look for child with a textblock.
My assumption is that if I click in white space I'm clicking in a container that has my textblock. So far the two things that come up are a Border and a Rectangle (if I don't click the text itself). A. Returns absolutely nothing except for the recangle and the border. When I do B i can find textblocks but they are every single text block in the entire row.
So what I try to do from that is get all textblocks, then go backwards till I find which one has a IsMouseOver property as true. It turns out none of these objects EVER have a IsMouseOver except the content presenter for the entire row. So this seems to indicate to me is that the whitespace in the cells does not actually contain the textblock.
What I find is that when I click on the Border and start looking at children, I eventually get to a container that has a rectangle (the rectangle I click) and a grid row view presenter. The presenter shows all of the objects inside the row (hence why i would get all textblocks when i do this recursive scan).
Here is some of the code used to do this to get an idea of what i'm doing. I have written about 10 different versions of this same recursive code generally attempting to find who has the Mouse over it and is related to a textbox.
private void OnPreviewMouseUp(object sender, MouseButtonEventArgs e)
{
object original = e.OriginalSource;
if (original is TextBlock)
{
this.valueTextBlock.Text = ((TextBlock)original).Text;
}
else if (original is FrameworkElement)
{
var result = GetAllNestedChildren<Border>(VisualTreeHelper.GetParent((DependencyObject)original)).Where(x => x.Name == "border").Where(x => HasAChildWithMouse(x)).ToList();
}
else
{
this.valueTextBlock.Text = string.Empty;
}
}
private bool HasAChildWithMouse(UIElement element)
{
if (element.IsMouseOver || element.IsMouseDirectlyOver)
return true;
var childCount = VisualTreeHelper.GetChildrenCount(element);
for (int i = 0; i < childCount; ++i)
{
var child = VisualTreeHelper.GetChild(element, i);
if (child is UIElement)
if (HasAChildWithMouse((UIElement)child))
return true;
}
return false;
}
private IEnumerable<T> GetAllNestedChildren<T>(DependencyObject obj) where T : UIElement
{
if (obj is T)
yield return obj as T;
var childCount = VisualTreeHelper.GetChildrenCount(obj);
for (int i = 0; i < childCount; ++i)
{
var child = VisualTreeHelper.GetChild(obj, i);
foreach (var nested in GetAllNestedChildren<T>(child))
yield return nested;
}
}
private T GetObjectByTypeParentHasMouse<T>(DependencyObject obj) where T : UIElement
{
if (obj is T)
{
if ((VisualTreeHelper.GetParent(obj) as UIElement).IsMouseOver )
{
return obj as T;
}
}
var childCount = VisualTreeHelper.GetChildrenCount(obj);
for (int i = 0; i < childCount; ++i)
{
var child = VisualTreeHelper.GetChild(obj, i);
var correctType = GetObjectByTypeParentHasMouse<T>(child);
if (correctType != null)
return correctType;
}
return null;
}
private T GetContainedType<T>(DependencyObject obj, bool checkForMouseOver) where T : UIElement
{
if (obj is T && ((T)obj).IsMouseOver)
return obj as T;
var childCount = VisualTreeHelper.GetChildrenCount(obj);
for (int i = 0; i < childCount; ++i)
{
var child = VisualTreeHelper.GetChild(obj, i);
var correctType = GetContainedType<T>(child, checkForMouseOver);
if (correctType != null)
return correctType;
}
return null;
}
The other approach I took was to start with the TextBlock itself, find its containing parent and find out how i can navigate to the answer. I find the templateparent is the ContentPresenter (named ="content") I find the grid, and then the border. The parent of the border is a content presenter whos content is the data view model for the entire row. The parent of this contentpresenter is the grid column's presenter. This is the same one that i was navigating up to in the other one.
It would appear that the first approach objects while are contain the cell do not actually contain the textblock or the entire cell templated items. It would appear to me there is no way to go from the Border or Rectangle that is clicked, back to the actual text field.
"Long story short" is there ANY way to make this connection?
(Btw I am not willing to give up this ListView/GridView because its payoffs far outweigh this negative and I'd gladly give up on this idea to keep the rest).
I think you sjould be able to either
1) Add some kind of (toggle)button to the root of your data template, and either bind to Command and handle it on your viewmodel or bind to IsChecked/IsPressed and handle changes via data triggers or w/e on the view side.
2) Add EventTrigger to your datatemplate at some point, and handle PreviewNouseUp/Down events there via simple animations.