Whats the difference b/w using Activity vs Application in Xamarin? Why would one want to use one approach over another?
For example, when I create a new Xamarin Form project in VS I get the follow:
[Activity(Label = "eApprove Main Activity", MainLauncher = true, Icon = "#drawable/eA_icon")]
public class MainActivity : Activity
{
...
}
I have also seen examples on internet where people are using Application class as their main Entry point:
namespace MyExpenses.Android
{
[Application(Theme = "#android:style/Theme.Holo.Light") ]
public class MyExpensesApplication : Application
{
public static Activity CurrentActivity { get; set; }
public MyExpensesApplication(IntPtr handle, global::Android.Runtime.JniHandleOwnership transer)
:base(handle, transer)
{
}
public override void OnCreate()
{
base.OnCreate();
}
}
}
Please make sure you do not confuse a classical Xamarin.Android app with the android portion of a Xamarin.Forms app. My quick and easy answer/recommendation would be that you would have one Application class per App project per platform and as many Activities as you like. The application is your entry point that kicks of any numbers activities based on your needs...
Related
I would to do a downloader app that save pictures to a folder. The app should work on windows and macos, and may be later on android and ios.
I haven't found a way to pick the target folder. Any idea on how it can be achieve either with blazor or xaml .NET MAUI app?
I've made a start implementing this for Windows and macOS. You can review the code here: https://github.com/jfversluis/MauiFolderPickerSample and wrote a little blog post about this as well here: https://blog.verslu.is/maui/folder-picker-with-dotnet-maui/
This follows kind of the basic pattern you'd want to use if you want to access platform-specific APIs:
Define an interface
Implement interface on each supported platform
Consume functionality
For this I have created a very simple but effective interface
public interface IFolderPicker
{
Task<string> PickFolder();
}
Then we create an implementation for Windows, by adding a new file FilePicker.cs to the Platforms\Windows\ folder. This makes it specific to Windows and allows us to write Windows specific code. The file contains this code:
using WindowsFolderPicker = Windows.Storage.Pickers.FolderPicker;
namespace MauiFolderPickerSample.Platforms.Windows
{
public class FolderPicker : IFolderPicker
{
public async Task<string> PickFolder()
{
var folderPicker = new WindowsFolderPicker();
// Make it work for Windows 10
folderPicker.FileTypeFilter.Add("*");
// Get the current window's HWND by passing in the Window object
var hwnd = ((MauiWinUIWindow)App.Current.Windows[0].Handler.PlatformView).WindowHandle;
// Associate the HWND with the file picker
WinRT.Interop.InitializeWithWindow.Initialize(folderPicker, hwnd);
var result = await folderPicker.PickSingleFolderAsync();
return result.Path;
}
}
}
Because I chose FolderPicker as the name for my own object here, there is a naming conflict with the Windows FolderPicker that is why there is that weird using at the top. If you go for MyFolderPicker as your object name that wouldn't be needed.
Now we register this interface and implementation with the generic host builder in our MauiProgram.cs:
public static class MauiProgram
{
public static MauiApp CreateMauiApp()
{
var builder = MauiApp.CreateBuilder();
builder
.UseMauiApp<App>()
.ConfigureFonts(fonts =>
{
fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
});
// Note: this part was added
#if WINDOWS
builder.Services.AddTransient<IFolderPicker, Platforms.Windows.FolderPicker>();
#elif MACCATALYST
builder.Services.AddTransient<IFolderPicker, Platforms.MacCatalyst.FolderPicker>();
#endif
builder.Services.AddTransient<MainPage>();
builder.Services.AddTransient<App>();
// Note: end added part
return builder.Build();
}
}
Note that I also added MainPage and App here so that our constructor injection works (have a look at MainPage.xaml.cs in the linked repository).
Now we can consume our functionality as follows:
namespace MauiFolderPickerSample;
public partial class MainPage : ContentPage
{
private readonly IFolderPicker _folderPicker;
public MainPage(IFolderPicker folderPicker)
{
InitializeComponent();
_folderPicker = folderPicker;
}
private async void OnPickFolderClicked(object sender, EventArgs e)
{
var pickedFolder = await _folderPicker.PickFolder();
FolderLabel.Text = pickedFolder;
SemanticScreenReader.Announce(FolderLabel.Text);
}
}
Implementing other platforms would require you to implement the interface for the platform you want to support and register it in the generic host builder. This should get you started for Windows and macOS.
Actually calling this should not be any different between .NET MAUI (regular) or .NET MAUI Blazor.
My Problem:
I use Shell with bottom Tabbar and I simply want to change it height on Android and maybe on iOS.
My Search Results:
I know that the Tabbar is an Android/iOS build in feature with solid specified height.
There seems to be a way to achieve that using a "Custom-Renderer". All projects I have found with this approach don't work with my visual studio (>100 Errors or simply does nothing).
I find it hard to believe that i need >100 rows of code to "only" adjust a height. Could someone provide a working solution to change the Shell Tabbar (bottom tabs) height ?
Edit
Unfourtounately you need to create a custom renderer on each platform project:
Android
MyShellRenderer class
[assembly: ExportRenderer(typeof(App.AppShell), typeof(App.Droid.MyShellRenderer))]
namespace App.Droid
{
public class MyShellRenderer : ShellRenderer
{
public MyShellRenderer(Context context) : base(context)
{
}
protected override IShellBottomNavViewAppearanceTracker CreateBottomNavViewAppearanceTracker(ShellItem shellItem)
{
return new MyBottomNavViewAppearanceTracker(this, shellItem);
}
}
}
MyBottomNavViewAppearanceTracker class
class MyBottomNavViewAppearanceTracker : ShellBottomNavViewAppearanceTracker
{
public MyBottomNavViewAppearanceTracker(IShellContext shellContext, ShellItem shellItem) : base(shellContext, shellItem)
{
}
public override void SetAppearance(BottomNavigationView bottomView, IShellAppearanceElement appearance)
{
bottomView.LayoutParameters.Height = 400;
base.SetAppearance(bottomView, appearance);
}
}
Edit:
iOS part credit goes to https://forums.xamarin.com/discussion/169894/how-to-change-shell-height-of-flyout-items-at-the-bottom-of-the-page
iOS
MyShellRenderer class
[assembly: ExportRenderer(typeof(App.AppShell), typeof(App.iOS.MyShellRenderer))]
namespace App.iOS
{
public class MyShellRenderer : ShellRenderer
{
protected override IShellTabBarAppearanceTracker CreateTabBarAppearanceTracker()
{
return new MyCreateTabBarAppearanceTracker();
}
}
}
CreateTabBarAppearanceTracker class
class CreateTabBarAppearanceTracker : ShellTabBarAppearanceTracker
{
public override void SetAppearance(UITabBarController controller, ShellAppearance appearance)
{
UITabBar tabBar = controller.TabBar;
int tabBarHeight = 100;
if (tabBar.Frame.Height != tabBarHeight)
{
tabBar.Frame = new CGRect(tabBar.Frame.X, tabBar.Frame.Y + (tabBar.Frame.Height - tabBarHeight), tabBar.Frame.Width, tabBarHeight);
}
}
}
Extras
You were probably missing some namespaces that would explains the abnormal big number of errors.
could not be found are you missing a using directive or an assembly reference
Usually people don't include namespaces (using statements) in answers because most of the time namespaces are obvious and are handled easily by visual studio intellisense.
Just put or hover the cursor on the red underlined statement and a small tooltip appears
Then click on "Show potential fix" or one of the keyboard shortcuts, select the appropriate fix (usually the first one of the suggested list), in this case intelisense will add the required namespace automatically.
Every Code example i have found has excluded the using directives. in my case i needed those following 3 which i wasnt able to find. Thanks to the answer of #Cfun the code above work with adding:
using Google.Android.Material.BottomNavigation;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
I'm trying to update the settings/preferences screen of my Xamarin Android app, which was using the PreferenceManager class. Since I'm targeting Android 10, this class is deprecated and I'd like to use the AndroidX.Preference library instead.
I followed Google's guide for making a settings screen with AndroidX. Here's the code I'm using
namespace SmartLyrics
{
[Activity(Label = "Settings", ConfigurationChanges = Android.Content.PM.ConfigChanges.ScreenSize | Android.Content.PM.ConfigChanges.Orientation, ScreenOrientation = Android.Content.PM.ScreenOrientation.Portrait)]
public class SettingsFragment : PreferenceFragmentCompat
{
public override void OnCreatePreferences(Bundle savedInstanceState, string rootKey)
{
AddPreferencesFromResource(Resource.Xml.perfs);
}
}
public class SettingsActivity : AppCompatActivity
{
protected override async void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
SetContentView(Resource.Layout.main_settings);
SupportFragmentManager
.BeginTransaction()
.Replace(Resource.Id.settingsContainer, new SettingsFragment()) //<--error here
.Commit();
}
}
}
I'm getting the error Cannot convert from 'SmartLyrics.SettingsFragment' to 'Android.Support.V4.App.Fragment'. I looked around online and couldn't find a workaround or anything about this error. I'd really like to use the AndroidX library to prevent any problems with unsupported code later on.
Any help is appreciated. Thanks!
Check which package AppCompatActivity refers to ?
If it：
using Android.Support.V7.App;
change it to :
using AndroidX.AppCompat.App;
I'm starting learning MVVM cross, In the android app, I have a splash screen class:
[Activity(MainLauncher = true,
Label = "#string/app_name",
Theme = "#style/Theme.Splash",
NoHistory = true,
ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation,
ScreenOrientation = ScreenOrientation.Portrait)]
public class SplashScreen : MvxSplashScreenActivity
{
public SplashScreen() : base(Resource.Layout.SplashScreen)
{
}
}
and this is the Setup class:
public class Setup : MvxAndroidSetup
{
protected Setup(Context applicationContext) : base(applicationContext)
{
}
protected override IMvxApplication CreateApp()
{
return null;
}
}
the problem is that the debugger doesn't hit the constructor of the Setup Class, instead I get "An unhandled exception" after the constructor of the splash screen
EDIT
I've already defined the App class in the PCL project:
public class App : MvxApplication
{
public override void Initialize()
{
base.Initialize();
}
also defined the AppStart:
public class AppStart : MvxNavigatingObject, IMvxAppStart
{
public async void Start(object hint = null)
{
//hardcoded login for this demo
//var userService = Mvx.Resolve<IUserDataService>();
//await userService.Login("gillcleeren", "123456");
ShowViewModel<MainViewModel>();
}
}
The main reason behind this project is to understand the sequence of code required and executed by MVVM Cross, so I provide the minimum code till it runs successfully without runtime errors.
Update
I have read your code again more thoroughly and I can see the issue now. You defined the constructor of the Setup class as protected, which makes it invisible for activation.
On MvvmCross for Android the magic happens inside MvxAndroidSetupSingleton class (see the source code here) which searches for the Setup type you defined. The FindSetupType method looks for your defined Setup class first and then inside the CreateSetup method Activator.CreateInstance is used to build the Setup instance. The CreateInstance method variant used however searches only for public constructors, which means it doesn't find your protected one. The result is that it cannot build the Setup class and crashes.
Original answer
The reason this happens is that you have no Core libary that would define the MvvmCross App class and would initialize other required setup. I suggest you to start with a simple tutorial or to look into the official sample projects to see what is necessary to make MvvmCross work in a Xamarin.Android app.
I'm currently reading the navigation section from An Introduction to Xamarin.Forms. One should use the GetMainPage() method. But how should that be used?
The default implementation of the app delegate looks like the following:
Applicaton Delegate:
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
public override bool FinishedLaunching (UIApplication app, NSDictionary options)
{
global::Xamarin.Forms.Forms.Init ();
LoadApplication (new App ());
return base.FinishedLaunching (app, options);
}
}
App:
public class App : Application
{
public App ()
{
MainPage = GetMainPage ();
}
public static Page GetMainPage()
{
var mainNav = new NavigationPage(new ListExample());
return mainNav;
}
}
I got it managed to use the GetMainPage()method instead of getting
Application windows are expected to have a root view controller at the end of application launch
If I look into the (old?) examples (example1, example2) the app delegate is different and a CreateViewController() method is available. In my case it is not!
What is the correct way of loading the root page on to the stack?
You don't have to use GetMainPage(); that's just a method you create. The way X.Forms works these days is: it exposes a MainPage property in the Xamarin.Forms Application class. You set this to an instance of a Page. How you create that page is up to you. You can either use
this.MainPage = new ContentPage { Content = ... }
or you create one file per page (which IMHO is best for maintainability):
this.MainPage = new MyLoginPage();
or you use helper methods which create your pages:
this.MainPage = this.GetMainPage();
The main page is the first page of your Forms application. You can set the MainPage property to a different value to show another page.
Earlier versions of Forms used different approaches and not all samples have been updated yet. Now all platforms only need a call to the Forms Init() method and a call to LoadApplication() instead of creating a view controller, an activity or a page (WP8).