Save Bitmap on Device in Xamarin Android

Question

I'm trying to save a generated bitmap on my device. The app is being developed in Xamarin.Android so the code is C#. If I run my app on the emulator (Android 10) it works but If I run it, on my device (Android 11) or emulator (Android 11), bitmap saved it is empty (bitmap file exists but it is 0kb).

Bitmap bitmap;

var imageView = FindViewById<ImageView>(Resource.Id.generatedImage);
Android.Graphics.Drawables.BitmapDrawable bitmapDrawable = ((Android.Graphics.Drawables.BitmapDrawable)imageView.Drawable);
if (bitmapDrawable != null)
{
   bitmap = bitmapDrawable.Bitmap;
   Java.IO.File path = Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads + Java.IO.File.Separator + $"{filename}.png");
   using (System.IO.FileStream os = new System.IO.FileStream(path.AbsolutePath, System.IO.FileMode.Create))
   {
       bitmap.Compress(Bitmap.CompressFormat.Png, 100, os);
       os.Close();
   }
}

I put in my AndroidManifest.xml:

<uses-sdk android:minSdkVersion="29" android:targetSdkVersion="30" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

and

android:requestLegacyExternalStorage="true"

What's wrong ?

Thanks
Alessio

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

ExternalStorageDirectory returns the root path of your external storage and will be deprecated in API 29:
https://developer.android.com/reference/android/os/Environment.html#getExternalStorageDirectory()
If you want to store your files into your own application's external storage you can try:

   string testPath= Android.App.Application.Context.GetExternalFilesDir("").AbsolutePath + $"{filename}.png";  

Here is my edited code.

   ImageView imageView = FindViewById<ImageView>(Resource.Id.imageView1);  
     
               //var imageView = FindViewById<ImageView>(Resource.Id.generatedImage);  
     
               string filename = "test";  
               Android.Graphics.Drawables.BitmapDrawable bitmapDrawable = ((Android.Graphics.Drawables.BitmapDrawable)imageView.Drawable);  
               if (bitmapDrawable != null)  
               {  
                   bitmap = bitmapDrawable.Bitmap;  
                    
                  string testPath= Android.App.Application.Context.GetExternalFilesDir("").AbsolutePath + $"{filename}.png";   
                   //       Java.IO.File path = ApplicationContext.GetExternalFilesDir(Android.OS.Environment.DirectoryDownloads + Java.IO.File.Separator + $"{filename}.png");;  
                   using (System.IO.FileStream os = new System.IO.FileStream(testPath, System.IO.FileMode.Create))  
                   {  
                       bitmap.Compress(Bitmap.CompressFormat.Png, 100, os);  
                       os.Close();  
                   }  
               }  

================================
Update===============================

I notice you used Android.Support.V4.App.ActivityCompat.RequestPermissions to request permission. It is not work in the Android11, please uninstall your application in the android emulator, then change it to AndroidX.AppCompat.App.ActivityCompat.RequestPermissions(this, permissions, 1);. And do not call PermissionCheck method in Oncreate method,I used your code, then run it in my emulator it worked.

First of all, please create a Navigation drawer app temple like following screenshot,

Then, Here is SplashActivity.cs

   using Android.App;  
   using Android.Content;  
   using Android.OS;  
   using Android.Runtime;  
   using Android.Views;  
   using Android.Widget;  
   using System;  
   using System.Collections.Generic;  
   using System.IO;  
   using System.Linq;  
   using System.Text;  
   using System.Threading.Tasks;  
     
   namespace App104  
   {  
       [Activity(Label = "SplashActivity", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]  
       public class SplashActivity : Activity  
       {  
           protected override void OnCreate(Bundle savedInstanceState)  
           {  
               base.OnCreate(savedInstanceState);  
               Window.AddFlags(WindowManagerFlags.Fullscreen);  
               Window.ClearFlags(WindowManagerFlags.Fullscreen);  
               Xamarin.Essentials.Platform.Init(this, savedInstanceState);  
               // Create your application here  
               LoadLayout();  
           }  
           private void LoadLayout()  
           {  
               Window.AddFlags(WindowManagerFlags.Fullscreen);  
               Window.ClearFlags(WindowManagerFlags.Fullscreen);  
     
               var color = Resources.GetColor(Resource.Color.colorBackground, this.ApplicationContext.Theme);  
               Window.SetNavigationBarColor(color);  
           }  
     
           protected override void OnResume()  
           {  
               base.OnResume();  
               SimulateStartup();  
           }  
     
           async void SimulateStartup()  
           {  
               await Task.Delay(1000);  
               //  string testPath =   
               var pathToNewFolder = Android.App.Application.Context.GetExternalFilesDir("").AbsolutePath;  
               if (!Directory.Exists(pathToNewFolder))  
               {  
                   Directory.CreateDirectory(pathToNewFolder);  
               }  
     
               Intent intent = new Intent("ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION");  
               intent.SetClass(this, typeof(MainActivity));  
               intent.SetType(typeof(MainActivity).ToString());  
               intent.AddCategory("android.intent.category.DEFAULT");  
               intent.SetData(Android.Net.Uri.Parse($"package:{ApplicationContext.PackageName}"));  
               StartActivity(intent);  
           }  
     
           public override void OnBackPressed() { }  
       }  
     
   }  

Here is MainActivity.cs

   using System;  
   using Android;  
   using Android.App;  
   using Android.Content;  
   using Android.Content.PM;  
   using Android.Graphics;  
   using Android.OS;  
   using Android.Runtime;  
   using Android.Views;  
   using Android.Widget;  
   using AndroidX.AppCompat.App;  
   using AndroidX.AppCompat.Widget;  
   using AndroidX.Core.App;  
   using AndroidX.Core.View;  
   using AndroidX.DrawerLayout.Widget;  
   using Google.Android.Material.FloatingActionButton;  
   using Google.Android.Material.Navigation;  
   using Google.Android.Material.Snackbar;  
     
   namespace App104  
   {  
       [Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar")]  
       public class MainActivity : AppCompatActivity, NavigationView.IOnNavigationItemSelectedListener  
       {  
           public static Context Context { get; set; }  
           protected override void OnCreate(Bundle savedInstanceState)  
           {  
               base.OnCreate(savedInstanceState);  
               Xamarin.Essentials.Platform.Init(this, savedInstanceState);  
               SetContentView(Resource.Layout.activity_main);  
               AndroidX.AppCompat.Widget.Toolbar toolbar = FindViewById<AndroidX.AppCompat.Widget.Toolbar>(Resource.Id.toolbar);  
               SetSupportActionBar(toolbar);  
               Context = this;  
               FloatingActionButton fab = FindViewById<FloatingActionButton>(Resource.Id.fab);  
               fab.Click += FabOnClick;  
     
               DrawerLayout drawer = FindViewById<DrawerLayout>(Resource.Id.drawer_layout);  
               ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar, Resource.String.navigation_drawer_open, Resource.String.navigation_drawer_close);  
               drawer.AddDrawerListener(toggle);  
               toggle.SyncState();  
     
               NavigationView navigationView = FindViewById<NavigationView>(Resource.Id.nav_view);  
               navigationView.SetNavigationItemSelectedListener(this);  
               PermissionCheck();  
           }  
     
           public override void OnBackPressed()  
           {  
               DrawerLayout drawer = FindViewById<DrawerLayout>(Resource.Id.drawer_layout);  
               if(drawer.IsDrawerOpen(GravityCompat.Start))  
               {  
                   drawer.CloseDrawer(GravityCompat.Start);  
               }  
               else  
               {  
                   base.OnBackPressed();  
               }  
           }  
     
           public override bool OnCreateOptionsMenu(IMenu menu)  
           {  
               MenuInflater.Inflate(Resource.Menu.menu_main, menu);  
               return true;  
           }  
     
           public override bool OnOptionsItemSelected(IMenuItem item)  
           {  
               int id = item.ItemId;  
               if (id == Resource.Id.action_settings)  
               {  
                   return true;  
               }  
     
               return base.OnOptionsItemSelected(item);  
           }  
     
           private void FabOnClick(object sender, EventArgs eventArgs)  
           {  
               View view = (View) sender;  
               Snackbar.Make(view, "Replace with your own action", Snackbar.LengthLong)  
                   .SetAction("Action", (Android.Views.View.IOnClickListener)null).Show();  
           }  
     
           public bool OnNavigationItemSelected(IMenuItem item)  
           {  
               int id = item.ItemId;  
     
               if (id == Resource.Id.nav_camera)  
               {  
                   // Handle the camera action  
               }  
               else if (id == Resource.Id.nav_gallery)  
               {  
     
               }  
               else if (id == Resource.Id.nav_slideshow)  
               {  
     
               }  
               else if (id == Resource.Id.nav_manage)  
               {  
     
               }  
               else if (id == Resource.Id.nav_share)  
               {  
     
               }  
               else if (id == Resource.Id.nav_send)  
               {  
     
               }  
     
               DrawerLayout drawer = FindViewById<DrawerLayout>(Resource.Id.drawer_layout);  
               drawer.CloseDrawer(GravityCompat.Start);  
               return true;  
           }  
          
           private void PermissionCheck()  
           {  
               if (CheckSelfPermission(Manifest.Permission.ReadExternalStorage) != Permission.Granted || CheckSelfPermission(Manifest.Permission.WriteExternalStorage) != Permission.Granted)  
               {  
                   var permissions = new string[] { Manifest.Permission.ReadExternalStorage, Manifest.Permission.WriteExternalStorage };  
                   ActivityCompat.RequestPermissions(this, permissions, 1);  
               }  
               else  
               {  
                   var input = FindViewById<TextView>(Resource.Id.inputNumber);  
                   Share(input.Text, Resources.GetString(Resource.String.title), Resources.GetString(Resource.String.share_msg));  
               }  
           }  
     
     
     
           public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Permission[] grantResults)  
           {  
               switch (requestCode)  
               {  
                   case 1:  
                       {  
                           // If request is cancelled, the result arrays are empty.   
                           if (grantResults.Length > 0 && grantResults[0] == Permission.Granted && grantResults[1] == Permission.Granted)  
                           {  
                               // permission was granted, yay! Do the contacts-related task you need to do.   
                               var input = FindViewById<TextView>(Resource.Id.inputNumber);  
                               Share(input.Text, Resources.GetString(Resource.String.title), Resources.GetString(Resource.String.share_msg));  
                           }  
                           else  
                           {  
                               // permission denied, boo! Disable the functionality that depends on this permission.   
                           }  
                           return;  
                       }  
     
                       // other 'case' lines to check for other permissions this app might request   
               }  
           }  
     
           
     
           public void Share(string filename, string title, string content)  
           {  
               if (string.IsNullOrEmpty(filename) || string.IsNullOrEmpty(title) || string.IsNullOrEmpty(content)) return;  
     
               var imageView = FindViewById<ImageView>(Resource.Id.generatedImage);  
               Android.Graphics.Drawables.BitmapDrawable bitmapDrawable = ((Android.Graphics.Drawables.BitmapDrawable)imageView.Drawable);  
               if (bitmapDrawable != null)  
               {  
                   Bitmap bitmap = bitmapDrawable.Bitmap;  
                   string testPath = Android.App.Application.Context.GetExternalFilesDir("").AbsolutePath + Java.IO.File.Separator + $"{filename}.png";  
                   using (System.IO.FileStream os = new System.IO.FileStream(testPath, System.IO.FileMode.Create))  
                   {  
                       bitmap.Compress(Bitmap.CompressFormat.Png, 100, os);  
                       os.Close();  
                   }  
     
                   var sharingIntent = new Intent();  
                   sharingIntent.SetAction(Intent.ActionSend);  
                   sharingIntent.SetType("image/*");  
                   sharingIntent.PutExtra(Intent.ExtraSubject, Resources.GetString(Resource.String.contact_subject));  
                   sharingIntent.PutExtra(Intent.ExtraText, content);  
                   sharingIntent.PutExtra(Intent.ExtraStream, testPath);  
                   StartActivity(Intent.CreateChooser(sharingIntent, title));  
               }  
           }  
     
           private void NavigationUrl(string url)  
           {  
               var uri = Android.Net.Uri.Parse(url);  
               var intent = new Intent(Intent.ActionView, uri);  
               StartActivity(intent);  
           }  
       }  
     }  

Then open the content_main.xml, add Imageview and textview like following xml

   <TextView  
           android:layout_width="wrap_content"  
           android:layout_height="wrap_content"  
           android:layout_centerInParent="true"  
           android:id="@+id/inputNumber"  
           android:text="Hello World!" />  
       <ImageView  
           android:layout_width="50dp"  
           android:layout_height="50dp"  
           android:id="@+id/generatedImage"  
           android:src="@drawable/icon1"/>  

==============
Update================

Please change the Bitmap.Config.Alpha8 to Bitmap.Config.Argb8888 in finalImage = Bitmap.CreateBitmap(width, height, Bitmap.Config.Argb8888); line, becuase we store colorful images, Bitmap.Config.Alpha8 just could install white or black image. for more details, you can refer to this thread.

Best Regards,

Leon Lu

---

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Answer 2

I find where is the problem but I don't know how to solve it. If I try to save a bitmap loaded from resources your code works but if I try to save a bitmap generated at run-time it doesn't work.

    public static Bitmap MergeImages(List<Bitmap> files)
    {
        if (files == null || files.Count == 0) return null;

        Canvas canvas = null;
        Rect baseRect = null;
        Rect frontRect = null;
        Bitmap finalImage = null;

        try
        {
            int width = files[0].Width;
            int height = files[0].Height;

            finalImage = Bitmap.CreateBitmap(width, height, Bitmap.Config.Alpha8);

            canvas = new Canvas(finalImage);
            frontRect = new Rect(0, 0, width, height);
            baseRect = new Rect(0, 0, width, height);

            foreach (var image in files)
            {
                canvas.DrawBitmap(image, frontRect, baseRect, null);
            }
            return finalImage;
        }
        catch (Exception)
        {
            canvas?.Dispose();
            baseRect?.Dispose();
            frontRect?.Dispose();
            finalImage?.Dispose();
            return null;
        }
    }

This is my code to merge a list of bitmap in a single bitmap (I display generated bitmap in my view). It seems it works because I can display it but if I try to save it I obtain 0Kb file size.

Thanks
Alessio