Xamarin forms template switch native content remains - xamarin.forms

I am seeing something strange where an instance of ContentView from a ControlTemplate affects how another instance of the ContentView looks, under the same page, from another ControlTemplate.
ContentView BLA:
ScrollView
L Accordion control
L Accordion Item
Control template A:
BLA
Control template B:
Tab control
L Tab 1 Content: BLA
L Tab 2 Content: other
Somehow switching ControlTemplate from A to B, B to A,
And the height of the accordion item remain from the first template.
It is not the same instance.
How can I make sure the native controls are disposed of when switching ControlTemplate?

Normally, we use DataTemplateSelector to switch templates.
For the Limitations in the MSdocs, the warnings, however the reason behind it, is due to the caching of templates in the renderer. If you change it up, the previous template will be cached in the renderer and there will be no longer any way to reference or dispose of it, until the ListView is disposed of. Hence as you scroll, it will continue to cache new templates and never free up the old ones.
Hope this would be helpful to you.
https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/templates/data-templates/selector

I moved away from template switching as the template is being cached, meaning the last view is still in memory, and this causes all kind of problems such as binding errors and layout measures turning out wrong.
I now use MyView which inherits ContentView:
public class MyView : ContentView
{
public static readonly BindableProperty DataProperty =
BindableProperty.Create(nameof(Data), typeof(object), typeof(MyView ), null, propertyChanging: OnDataPropertyChanging);
public object Data
{
get => (object)GetValue(DataProperty);
set => SetValue(DataProperty, value);
}
private static void OnDataPropertyChanging(BindableObject bindable, object oldValue, object newValue)
{
var instance = bindable as MyViewModel;
instance.Content = null;
if (newValue == null)
{
return;
}
var type = newValue.GetType();
View view = null;
if (type == typeof(MyViewModel1))
{
view = new BLA();
}
else if (type == typeof(MyViewModel2))
{
view = new other();
}
if (view != null)
{
view.BindingContext = newValue;
instance.Content = view;
}
}
}

Related

How could I change the Navigastion's page arrow in Xamarin Forms?

I'm creating an app using xamarin Forms (multiplatform), I'm using a Navigation page, but I want to change the arrow ("<-") to text ("back")
Do you know how could i do it?
Thanks
(I'm going to use it in an Android App, but I'm creating the app using Xamarin forms)
You could use custom renderer to remove the navigation icon and set it with text. But, when you do that, you need to capture the click of the text and simulate the back event.
Create the interface:
public class CustomNavigationPage : NavigationPage
{
public CustomNavigationPage(Page startupPage) : base(startupPage)
{
}
}
The implementation of Android:
[assembly: ExportRenderer(typeof(CustomNavigationPage),
typeof(NavigationPageRenderer_Droid))]
namespace NavigationPageDemo.Droid
{
public class NavigationPageRenderer_Droid : NavigationPageRenderer
{
public Android.Support.V7.Widget.Toolbar toolbar;
public Activity context;
public NavigationPageRenderer_Droid(Context context) : base(context)
{
}
protected override Task<bool> OnPushAsync(Page view, bool animated)
{
var retVal = base.OnPushAsync(view, animated);
context = (Activity)Forms.Context;
toolbar = context.FindViewById<Android.Support.V7.Widget.Toolbar>(Droid.Resource.Id.toolbar);
if (toolbar != null)
{
//if (toolbar.NavigationIcon != null)
//{
//toolbar.NavigationIcon = Android.Support.V7.Content.Res.AppCompatResources.GetDrawable(context, Resource.Drawable.back);
//toolbar.NavigationIcon = null;
toolbar.NavigationIcon = null;
toolbar.Title = "back";
toolbar.SetOnClickListener(new OnClick());
//}
}
return retVal;
}
protected override Task<bool> OnPopViewAsync(Page page, bool animated)
{
return base.OnPopViewAsync(page, animated);
}
}
public class OnClick : Java.Lang.Object, IOnClickListener
{
void IOnClickListener.OnClick(Android.Views.View v)
{
App.Current.MainPage.Navigation.PopAsync();
}
}
In the custom renderer, use the OnClickListener to capture the click on text.
when you are working with xamarin forms it is suggested make use of common components and make least use of custom renderer.
Now for your requirement you want to create custom navigation bar
so here is how you can do it.
Create BaseContent Page
Create a Control Template inside your base page your can follow this link
Inside your control template using a grid view place your label with text binding (Back),also your can place a label in center to show title of page again u can make use of template binding which u would come to know when u go through the link
Now inherit your main page with your basecontentpage page
add your control template inside your main page
turn off your navigation bar of your main page
and you are done, this would give u more power to add more things like image or toolbar in your navbar
also to dynamically handle your back button u can check the count from navigationstack if its 0 u can show Humburger Icon or if its more than 0 u can show your label using IsVisible True/False

Prevent column width resizing

How can I prevent column width resizing? I have a table, and I'm wondering if I can simply disable the option to drag to resize width of the columns. Is there any way to do this, or will I have to manually set the max and min width of each column just so that it can't be manipulated by the user? The problem with this is that the text in the title/header of my table is smaller than what's in the row underneath it. Setting the width to the column width forces it smaller, and then you can't see the info in the cell underneath.
Also, if there's a way to disable rearranging the columns, that'd be nice too. I basically want what I have set to not be changed at all. If this can't be done, I might just replace each table with an image of itself, so that it can't be manipulated at all.
Prevent Resizing Columns
From here, we can know that setResizable(boolean) allows you to choose whether the user can resize a column. Setting the max and min width to the same value does prevents the user from resizing the column, but not a preferred method. Also, the user will see the resizing cursor but not the default cursor when attempting to resize the column.
Prevent Reordering Columns
JavaFX 9
For preventing the user from reordering the columns, there isn't a straight-forward solution until JavaFX 9, which introduces setReorderable(boolean), isReorderable(), reorderableProperty methods, and the reorderable field in the TableColumnBase class. Here is a snippet of the source code:
package javafx.scene.control;
//some imports and JavaDoc comments
#IDProperty("id")
public abstract class TableColumnBase<S,T> implements EventTarget, Styleable {
//some code
// --- Reorderable
/**
* A boolean property to toggle on and off the 'reorderability' of this column
* (with drag and drop - reordering by modifying the appropriate <code>columns</code>
* list is always allowed). When this property is true, this column can be reordered by
* users simply by dragging and dropping the columns into their desired positions.
* When this property is false, this ability to drag and drop columns is not available.
*
* #since 9
*/
private BooleanProperty reorderable;
public final BooleanProperty reorderableProperty() {
if (reorderable == null) {
reorderable = new SimpleBooleanProperty(this, "reorderable", true);
}
return reorderable;
}
public final void setReorderable(boolean value) {
reorderableProperty().set(value);
}
public final boolean isReorderable() {
return reorderable == null ? true : reorderable.get();
}
//some code
}
If your application bases on JavaFX 9, then you are lucky. Simply invoke setReorderable(false) on your desired table column and there you go.
JavaFX 8
If your application bases on JavaFX 8 or older versions, you can use com.sun.javafx.scene.control.skin.TableHeaderRow, which has isReordering, setReordering, reorderingProperty methods, and reorderingProperty field. Here is a snippet of the source code:
package com.sun.javafx.scene.control.skin;
//some imports and JavaDoc comments
public class TableHeaderRow extends StackPane {
//some code
private BooleanProperty reorderingProperty = new BooleanPropertyBase() {
#Override protected void invalidated() {
TableColumnHeader r = getReorderingRegion();
if (r != null) {
double dragHeaderHeight = r.getNestedColumnHeader() != null ?
r.getNestedColumnHeader().getHeight() :
getReorderingRegion().getHeight();
dragHeader.resize(dragHeader.getWidth(), dragHeaderHeight);
dragHeader.setTranslateY(getHeight() - dragHeaderHeight);
}
dragHeader.setVisible(isReordering());
}
#Override
public Object getBean() {
return TableHeaderRow.this;
}
#Override
public String getName() {
return "reordering";
}
};
public final void setReordering(boolean value) { reorderingProperty().set(value); }
public final boolean isReordering() { return reorderingProperty.get(); }
public final BooleanProperty reorderingProperty() { return reorderingProperty; }
//some code
}
The methods and fields work the same as the one in TableColumnBase in JavaFX 9, just with different names.
You want to obtain the TableHeaderRow object as a children of the skin of the TableView:
TableView<MyType> table = new TableView<MyType>();
//some code
//DISPLAY THE TABLE OR GETSKIN WILL RETURN NULL
com.sun.javafx.scene.control.skin.TableHeaderRow header = null;
for (Node node : table.getSkin().getChildren())
if (node instanceof com.sun.javafx.scene.control.skin.TableHeaderRow)
header = (com.sun.javafx.scene.control.skin.TableHeaderRow) node;
if (header == null); //Table not rendered
header.setReorderable(false);
You must have the TableView rendered before accessing the skin, because the TableViewSkin obtained from TableView.getSkin() is a visual representation of user interface controls. As the official JavaFx JavaDoc says, Skin is a
Base class for defining the visual representation of user interface
controls by defining a scene graph of nodes to represent the skin. A
user interface control is abstracted behind the Skinnable interface.
Therefore, the Skin will be null if the TableView is not rendered because there is nothing visual to represent.
Note that the second method cannot be used in Java 9 or later due to the modules in Java API block your access towards any sun packages.
EDIT:
In JavaFX 8 or older, there is a method called impl_setReorderable(boolean) which is deprecated, but works flawlessly, pretty much same as setReorderable(boolean) in JavaFX 9.

how to fill in combobox dynamically with caliburn micro?

I am new to MVVM and Caliburn.Micro.
I am trying to do a simple application using Caliburn.Micro that has a combobox.
The combobox items are added dynamically when the program is running, the problem is that the combobox stops updating its content after the first item navigation.
In View:
The combobox is declared as follows:
<ComboBox x:Name="cmbProductList" />
In ViewModel:
I declare the following list for combobox items:
List<string> L = new List<string> { };
I am using the following method to fill combobox item:
public List<string> cmbProductList
{
get
{
return L;
}
set
{
L = value;
NotifyOfPropertyChange("cmbProductList");
}
}
And this command to add an item to this list:
L.Add(p1.ID.ToString());
The container you are using for your combobox items is not the proper one. List has no way of notifying the UI of its changes (items added or removed). Instead you need to use an ObservableCollection. Or even better, you can use BindableCollection that is Caliburn.Micro's customized version of ObservableCollection:
BindableCollection is a simple collection that inherits from ObservableCollection, but that ensures that all its events are raised on the UI thread as well.
http://caliburnmicro.com/documentation/introduction
Your property would look like this:
private BindableCollection<string> _cmbProductList;
public BindableCollection<string> cmbProductList
{
get
{
return _cmbProductList;
}
set
{
_cmbProductList = value;
NotifyOfPropertyChange("cmbProductList");
}
}
and of course its initialization would look like this:
_cmbProductList = new BindableCollection<string>();
The rest can stay unchanged.

.NET 4.0 DataGridCombobox SelectionChanged issue

I have a requirement in my program that the object bound (from ViewModel) in a Combobox is updated as soon as an item is selected in the combobox. Currently, the object only updates once the edit is committed by either pressing Enter or leaving the cell. The user does not want the extra step.
My thought would be to have the act of selecting an item in the combobox trigger the CommitEdit() method and then CancelEdit(). However, I cannot seem to find a way to hook into the SelectionChanged event for the DataGridComboBoxColumn as it is not available.
Other suggestions have been to listen in the viewmodel for a property change event but the property is not changed until the Cell Edit is finished.
Can anyone think of a way to cause the selection of a new item (index) in a DataGridCombobox to close the edit of the cell as if the user pressed Enter or left the cell?
NOTE: I cannot use .NET 4.5 due to customer limitations.
I've had similar issue but i just found out the solution using attached property, This may not exactly fix your problem but it will help in datagrid selection changed issue.
Below is the attached property and handler methods
public static readonly DependencyProperty ComboBoxSelectionChangedProperty = DependencyProperty.RegisterAttached("ComboBoxSelectionChangedCommand",
typeof(ICommand),
typeof(SpDataGrid),
new PropertyMetadata(new PropertyChangedCallback(AttachOrRemoveDataGridEvent)));
public static void AttachOrRemoveDataGridEvent(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
DataGrid dataGrid = obj as DataGrid;
if (dataGrid != null)
{
if (args.Property == ComboBoxSelectionChangedProperty)
{
dataGrid.SelectionChanged += OnComboBoxSelectionChanged;
}
}
else if (args.OldValue != null && args.NewValue == null)
{ if (args.Property == ComboBoxSelectionChangedProperty)
{
dataGrid.SelectionChanged -= OnComboBoxSelectionChanged;
}
}
}
private static void OnComboBoxSelectionChanged(object sender, SelectionChangedEventArgs args)
{
DependencyObject obj = sender as DependencyObject;
ICommand cmd = (ICommand)obj.GetValue(ComboBoxSelectionChangedProperty);
DataGrid grid = sender as DataGrid;
if (args.OriginalSource is ComboBox)
{
if (grid.CurrentCell.Item != DependencyProperty.UnsetValue)
{
//grid.CommitEdit(DataGridEditingUnit.Row, true);
ExecuteCommand(cmd, grid.CurrentCell.Item);
}
}
}
SpDataGrid is the custom control that i inherited from data grid.
I added below style in generic.xaml as i use the resourcedictionary for style (you can certainly add inside the datagrid).
<Style TargetType="{x:Type Custom:SpDataGrid}">
<Setter Property="Custom:SpDataGrid.ComboBoxSelectionChangedCommand" Value="{Binding ComboBoxSelectionChanged}"/>
</Style>
ComboBoxSelectionChanged is the command in my viewmodel. OnComboBoxSelectionChanged i commented the commitedit because in my case the values were already updated.
Let me know if anything is not clear or any questions. Hope this helps.

Structuring a MonoTouch.Dialog application

From the examples at Xamarin.com you can build basic M.T. Dialog apps, but how do you build a real life application?
Do you:
1) Create a single DialogViewController and tree every view/RootElement from there or,
2) Create a DialogViewController for every view and use the UINavigationController and push it on as needed?
Depending on your answer, the better response is how? I've built the example task app, so I understand adding elements to a table, click it to go to the 'next' view for editing, but how to click for non-editing? How to click a button, go next view if answer is number 1?
Revised:
There is probably no one right answer, but what I've come up with seems to work for us. Number 2 from above is what was chosen, below is an example of the code as it currently exists. What we did was create a navigation controller in AppDelegate and give access to it throughout the whole application like this:
public partial class AppDelegate : UIApplicationDelegate
{
public UIWindow window { get; private set; }
//< There's a Window property/field which we chose not to bother with
public static AppDelegate Current { get; private set; }
public UINavigationController NavController { get; private set; }
public override bool FinishedLaunching (UIApplication app, NSDictionary options)
{
Current = this;
window = new UIWindow (UIScreen.MainScreen.Bounds);
NavController = new UINavigationController();
// See About Controller below
DialogViewController about = new AboutController();
NavController.PushViewController(about, true);
window.RootViewController = NavController;
window.MakeKeyAndVisible ();
return true;
}
}
Then every Dialog has a structure like this:
public class AboutController : DialogViewController
{
public delegate void D(AboutController dvc);
public event D ViewLoaded = delegate { };
static About about;
public AboutController()
: base(about = new About())
{
Autorotate = true;
about.SetDialogViewController(this);
}
public override void LoadView()
{
base.LoadView();
ViewLoaded(this);
}
}
public class About : RootElement
{
static AboutModel about = AboutVM.About;
public About()
: base(about.Title)
{
string[] message = about.Text.Split(...);
Add(new Section(){
new AboutMessage(message[0]),
new About_Image(about),
new AboutMessage(message[1]),
});
}
internal void SetDialogViewController(AboutController dvc)
{
var next = new UIBarButtonItem(UIBarButtonSystemItem.Play);
dvc.NavigationItem.RightBarButtonItem = next;
dvc.ViewLoaded += new AboutController.D(dvc_ViewLoaded);
next.Clicked += new System.EventHandler(next_Clicked);
}
void next_Clicked(object sender, System.EventArgs e)
{
// Load next controller
AppDelegate.Current.NavController.PushViewController(new IssuesController(), true);
}
void dvc_ViewLoaded(AboutController dvc)
{
// Swipe location: https://gist.github.com/2884348
dvc.View.Swipe(UISwipeGestureRecognizerDirection.Left).Event +=
delegate { next_Clicked(null, null); };
}
}
Create a sub-class of elements as needed:
public class About_Image : Element, IElementSizing
{
static NSString skey = new NSString("About_Image");
AboutModel about;
UIImage image;
public About_Image(AboutModel about)
: base(string.Empty)
{
this.about = about;
FileInfo imageFile = App.LibraryFile(about.Image ?? "filler.png");
if (imageFile.Exists)
{
float size = 240;
image = UIImage.FromFile(imageFile.FullName);
var resizer = new ImageResizer(image);
resizer.Resize(size, size);
image = resizer.ModifiedImage;
}
}
public override UITableViewCell GetCell(UITableView tv)
{
var cell = tv.DequeueReusableCell(skey);
if (cell == null)
{
cell = new UITableViewCell(UITableViewCellStyle.Default, skey)
{
SelectionStyle = UITableViewCellSelectionStyle.None,
Accessory = UITableViewCellAccessory.None,
};
}
if (null != image)
{
cell.ImageView.ContentMode = UIViewContentMode.Center;
cell.ImageView.Image = image;
}
return cell;
}
public float GetHeight(UITableView tableView, NSIndexPath indexPath)
{
float height = 100;
if (null != image)
height = image.Size.Height;
return height;
}
public override void Selected(DialogViewController dvc, UITableView tableView, NSIndexPath indexPath)
{
//base.Selected(dvc, tableView, path);
tableView.DeselectRow(indexPath, true);
}
}
#miquel
The current idea of a workflow is an app that starts with a jpg of the Default.png that fades into the first view, with a flow control button(s) that would move to the main app. This view, which I had working previous to M.T.D. (MonoTouch.Dialog), which is a table of text rows with an image. When each row is clicked, it moves to another view that has the row/text in more detail.
The app also supports in-app-purchasing, so if the client wishes to purchase more of the product, then switch to another view to transact the purchase(s). This part was the main reason for switching to M.T.D., as I thought M.T.D. would be perfect for it.
Lastly there would be a settings view to re-enable purchases, etc.
PS How does one know when the app is un-minimized? We would like to show the fade in image again.
I have been asking myself the same questions. I've used the Funq Dependency Injection framework and I create a new DialogViewController for each view. It's effectively the same approach I've used previously developing ASP.NET MVC applications and means I can keep the controller logic nicely separated. I subclass DialogViewController for each view which allows me to pass in to the controller any application data required for that particular controller. I'm not sure if this is the recommended approach but so far it's working for me.
I too have looked at the TweetStation application and I find it a useful reference but the associated documentation specifically says that it isn't trying to be an example of how to structure a MonoTouch application.
I use option 2 that you stated as well, it works pretty nicely as you're able to edit the toolbar options on a per-root-view basis and such.
Option 2 is more feasible, as it also gives you more control on each DialogViewController. It can also helps if you want to conditionally load the view.

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