We Keep Coding

Xamarin cache pages - make it so input doesn't disappear

I'm building my first full-scale Xamarin.Forms app and trying to figure out how to keep user input between navigation. After doing some searching online I've read that the default behavior is to completely reload pages each time you navigate, but you can change the default behavior by setting the NavigationCacheMode to true or required, but I've tried to set this attribute in both xaml and C# with no success - it seems like the property is not recognized.
Is there a simple way to make it so that user input does not disappear when navigating between pages? If anyone can show me how to set the NavigationCacheMode that would be great, but I'm also open to any reasonable solution that will keep the user input from disappearing during navigation.
Additional details: My app has a UWP and Android project. I am using a master detail page for navigation. Here is my MenuList_ItemSelected event handler:
private void MenuList_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
var item = (MenuItem)e.SelectedItem;
var title = item.Title;
var page = (Page)Activator.CreateInstance(item.TargetType);
Detail = new NavigationPage(page); //TODO: when menu item is clicked and you're already on that page, the menu should just slide back. (currently it does nothing and stays out).
IsPresented = false;
}

Finally was able to solve this! I adapted this code from a related post which implements a Dictionary that keeps track of the navigation stack:
In the constructor for my Master Detail Page:
public partial class MenuPage : MasterDetailPage
{
Dictionary<Type, Page> menuCache = new Dictionary<Type, Page>();
}
Then in the ItemSelected method:
private void MenuList_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
if (menuCache.Count == 0)
menuCache.Add(typeof(AttendancePage), Detail);
var item = (MenuItem)e.SelectedItem;
if (item != null)
{
if (menuCache.ContainsKey(item.TargetType))
{ Detail = menuCache[item.TargetType]; }
else
{
Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType));
menuCache.Add(item.TargetType, Detail);
}
menuList.SelectedItem = null; //solves issue with nav drawer not hiding when same item is selected twice
IsPresented = false;
}
}

Can't see Loaded, Initialized, Visible window

Simplified version
ParentWindow.ShowDialog()
Click default/Bring Up Child Window button in ParentWindow
Click event handler for default/Bring Up Child Window button does ParentWindow.Hide()
ChildWindow.ShowDialog()
Click ChildWindow's cancel/Go Back button
ParentWindow.Visibility = Visibility.Visible
ParentWindow is nowhere to be found.
I checked, and ParentWindow returns true for IsInitialized, IsLoaded, and IsVisible. I also Alt-Tabbed my way through all my windows to look for it - it's not hiding under anything.
Why can't I see ParentWindow anywhere?
Full version
parseSettingsWindow.ShowDialog()
Click default/Bring Up Fix Selector button in parseSettingsWindow
Click event handler for default/Bring Up Fix Selector button does:
a. ParentWindow.Hide()
b. parseSettingsWindow.GoToNextWindow flag set to true (Next window is Fix Selector)
while loop does fixSelector.ShowDialog() because it's not yet loaded
Click ChildWindow's cancel/Go Back button
while loop is entered again, goes to `case "Parse Settings" section
parseSettingsWindow.Visibility = Visibility.Visible
parseSettingsWindow is nowhere to be found
I checked, and parseSettingsWindow returns true for IsInitialized, IsLoaded, and IsVisible in the Immediate Window when pausing execution on the break; line of the "Parse Settings" while loop section. I also Alt-Tabbed my way through all my windows to look for it - it's not hiding under anything.
Why can't I see parseSettingsWindow anywhere?
Main class
public static bool UserPromptedSettingsWereWrittenToModel(ref Model model, ref ActiveFixes activeFixes, ref ActiveReports activeReports)
{
var viewModel = new ViewModel();
var parseSettingsWindow = new ViewPlusViewModel.ParseSettings();
parseSettingsWindow.InitializeComponent();
var fixSelector = new ViewPlusViewModel.FixSelector(viewModel);
fixSelector.InitializeComponent();
var seeAllFixesReports = new ViewPlusViewModel.SeeAllFixesReports();
seeAllFixesReports.InitializeComponent();
parseSettingsWindow.ShowDialog();
var nextWindowToOpen = "Fix Selector";
while (parseSettingsWindow.GoToNextWindow == true && fixSelector.GoToNextWindow == false)
{
switch(nextWindowToOpen)
{
case "Fix Selector":
if (fixSelector.IsLoaded)
{
fixSelector.Visibility = Visibility.Visible;
}
else
{
fixSelector.ShowDialog();
}
nextWindowToOpen = "Parse Settings";
break;
case "Parse Settings":
parseSettingsWindow.GoToNextWindow = false;
parseSettingsWindow.Visibility = Visibility.Visible;
nextWindowToOpen = "Fix Selector";
break;
}
}
if (parseSettingsWindow.GoToNextWindow == false)
{
parseSettingsWindow.Close();
if (fixSelector.IsLoaded) fixSelector.Close();
if (seeAllFixesReports.IsLoaded) { seeAllFixesReports.Close(); }
return false;
}
parseSettingsWindow.Close();
fixSelector.Close();
if (seeAllFixesReports.IsLoaded) { seeAllFixesReports.Close(); }
return true;
}
ParseSettingsWindow.cs
private void GoToNextWindow_Click(object sender, RoutedEventArgs e)
{
this.GoToNextWindow = true;
this.Hide();
}

You can't bring a hidden .ShowDialog() window back again via Window.Visibility. You need to use .ShowDialog() on it again. In addition, any buttons given the IsCancel = True property will no longer have that functionality even when using ShowDialog() again, so presses on that button will need to be handled manually.

Jumping to next tab

I have a tab control in my WPF application with multiple tabs. Each tab gives access to several buttons, text boxes, drop downs. Now before moving to the next tab valid entries in each of the controls in the tab is to be checked or jumping to the next tab should not be allowed. How can this be done?
I was able to use IsEnable property to do this. But I want it like, when I click on the next tab it should, without entering the next tab, display a warning that such and such entry in the present tab is not valid.

If you adhere to the Selected event you can do something like this:
// Keep a global variable for the previous index
int prevIndex = 0;
private void tabControl_Selected(object sender, TabControlEventArgs e)
{
TabControl tc = sender as TabControl;
if (tc != null)
{
bool letSwitchHappen = validateTabControls(tc.SelectedIndex);
if (!letSwitchHappen)
{
tc.SelectedIndex = prevIndex;
}
prevIndex = tc.SelectedIndex;
}
}
Where validateTabControls is something like:
private bool validateTabControls(int tabIndex)
{
bool validEntries = false;
// Some code here to set validEntries according to the control at tabIndex
return validEntries;
}

Take a look at this example from Josh Smith.
It shows explicitly how to do this, and Josh is well-known (and respected) in the WPF world.

Disabling a ToolStripMenuItem vs. disabling a MenuStrip.Item

When a user logs into my application, there are some menu items that I don't want every user to see. So I would like to either disable or make invisible the menu item. For example fileToolStripMenuItem is the first item in my menuStrip, when I try:
fileToolStripMenuItem.Enabled = false; - this does not work
menuStrip.Items[0].Enabled = false; - this does work
Can anyone enlighten me as to the difference here?
Also, I would like to be able to disable a drop down item from one of the menu items, but I cannot do that either.
Here's the code:
public Form1()
{
InitializeComponent();
// bunch of other code here
if (!login.ValidatedUser)
{
menuStrip1.Items[0].Visible = false; // this works
toolsToolStripMenuItem.Visible = false; // this does not
btnStartResourceManager.Enabled = false;
listAvailableSizes.Enabled = true;
panelPicSet.Enabled = true;
}
}

fileToolStripMenuItem.Enabled = false; works as expected. I think you trying to disable it before InitializeComponent(); call.
public form()
{
InitializeComponent();
fileToolStripMenuItem.Enabled = false;//disables all file menu
saveasToolStripMenuItem.Enabled = false; //disables save as menu item in file menu list
}

Use the specific name of your menu item and change its Visible property. i.e.
private void toggleToolStripMenuItem_Click(object sender, EventArgs e)
{
if (shown)
saveToolStripMenuItem.Visible = false;
else
saveToolStripMenuItem.Visible = true;
shown = !shown;
}

For Sub Items, just right click on the item and see its name In Design Section in Properties Window. In my case below addNewToolStripMenuItem1.
public Form()
{
InitializeComponent();
menuStrip1.Items[1].Visible = false; // For Main Item // Bold Letters
addNewToolStripMenuItem1.Visible = false; //For Sub Items
}

Change mouse pointer from hand to I

I am using gird view which have read write access
using password user can login and on its password he can read or write on the grid view
on grid view i have asp:button i disable it by using grid view's command event
protected void gvMemSpb_RowCreated(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
int iRow = int.Parse(Convert.ToString(e.Row.RowIndex));
if (iRow > -1)
{
if (Session["Me_Status"].ToString() == "" || Session["Me_Status"].ToString() == "R")
{
e.Row.Cells[3].Enabled = false;
e.Row.Cells[4].Enabled = false;
e.Row.Cells[5].Enabled = false;
lblRWAccess.Text = "This is (read only) Access page";
}
}
}
This is how i disable the asp:button on grid view, they get disable,
but the problem is that it is still showing hand icon on it when mouse over those buttons,
i do not want to show hand pointer on mouse over event i lot search on google but could not find probable solution how to hide the hand pointer pragmatically
{
?//what code i add hear to hide hand pointer
?
?
e.Row.Cells[3].Enabled = false;
e.Row.Cells[4].Enabled = false;
e.Row.Cells[5].Enabled = false;
lblRWAccess.Text = "This is (read only) Access page";
}
Thanks in advance
Vaibhav Deshpande(MCA)

I would use CSS to modify the button's cursor when it is disabled, upon disable you could add a class that changes the cursor from it's default to what you desire and upon enable you remove the class. CSS would be like
nohand { cursor: text; } /* this should change the cursor to the I-bar when added to an html element */