Develop Reference

Xamarin Android take screenshot

I am working on a project which makes drawing.
I don't use axml because I do my drawing in a class called filledpolygon and calling the function in MainActivity. I just want to take screenshot in my project. Is there any basic function, which I can call in onCreate method? So, when the program runs, it will automatically take the screenshot. I found answers except Xamarin platform.

Since Android 28 DrawingCacheEnabled is deprecated and without it we are forcing our view to to redraw on our custom canvas wich can cause artifacts with custom controls and renderers and the screenshot version might be different from what we see on screen.
The legacy code that is still working on simple cases is:
public byte[] CaptureScreenshot()
{
var view=
Xamarin.Essentials.Platform.CurrentActivity.Window.DecorView.RootView;
if (view.Height < 1 || view.Width < 1)
return null;
byte[] buffer = null;
view.DrawingCacheEnabled = true;
using (var screenshot = Bitmap.CreateBitmap(
view.Width,
view.Height,
Bitmap.Config.Argb8888))
{
var canvas = new Canvas(screenshot);
view.Draw(canvas);
using (var stream = new MemoryStream())
{
screenshot.Compress(Bitmap.CompressFormat.Png, 90, stream);
buffer = stream.ToArray();
}
}
view.DrawingCacheEnabled = false;
return buffer;
}
Use legacy method above as follows
if ((int)Android.OS.Build.VERSION.SdkInt < 28)
{
//legacy
}
The DrawingCacheEnabled obsolete warning redirects us to use PixelCopy. This method is acting with a callback so to use it synchronously have made some helpers:
Usage:
public byte[] CaptureScreenshot()
{
using var helper = new ScreenshotHelper(
Xamarin.Essentials.Platform.CurrentActivity.Window.DecorView.RootView,
Xamarin.Essentials.Platform.CurrentActivity);
byte[] buffer = null;
bool wait = true;
Task.Run(async () =>
{
helper.Capture((Bitmap bitmap) =>
{
try
{
if (!helper.Error)
{
using (var stream = new MemoryStream())
{
bitmap.Compress(Bitmap.CompressFormat.Png, 90, stream);
buffer = stream.ToArray();
}
}
}
catch (Exception e)
{
Console.WriteLine(e);
}
finally
{
wait = false;
}
});
}).ConfigureAwait(false);
while (wait)
{
Task.Delay(10).Wait();
}
return buffer;
}
The helper:
public class ScreenshotHelper : Java.Lang.Object, PixelCopy.IOnPixelCopyFinishedListener
{
public void OnPixelCopyFinished(int copyResult)
{
var stop = true;
if (copyResult == (int) PixelCopyResult.Success)
{
Error = false;
//todo CallbackGotScreenshot();
_callback(_bitmap);
}
else
{
Error = true;
}
_callback(_bitmap);
}
public bool Error { get; protected set; }
public ScreenshotHelper(Android.Views.View view, Activity activity)
{
_view = view;
_activity = activity;
_bitmap = Bitmap.CreateBitmap(
_view.Width,
_view.Height,
Bitmap.Config.Argb8888);
}
// Starts a background thread and its {#link Handler}.
private void StartBackgroundThread()
{
_BackgroundThread = new HandlerThread("ScreeshotMakerBackground");
_BackgroundThread.Start();
_BackgroundHandler = new Handler(_BackgroundThread.Looper);
}
// Stops the background thread and its {#link Handler}.
private void StopBackgroundThread()
{
try
{
_BackgroundThread.QuitSafely();
_BackgroundThread.Join();
_BackgroundThread = null;
_BackgroundHandler = null;
}
catch (Exception e)
{
//e.PrintStackTrace();
}
}
public void Capture(Action<Bitmap> callback)
{
//var locationOfViewInWindow = new int[2];
//_view.GetLocationInWindow(locationOfViewInWindow);
_callback = callback;
try
{
StartBackgroundThread();
//todo could create-use background handler
PixelCopy.Request(_activity.Window, _bitmap, this,
_BackgroundHandler);
}
catch (Exception e)
{
Console.WriteLine(e);
}
finally
{
Task.Run(StopBackgroundThread);
}
}
private Android.Views.View _view;
private Activity _activity;
private Bitmap _bitmap;
private HandlerThread _BackgroundThread;
private Handler _BackgroundHandler;
private Action<Bitmap> _callback;
public new void Dispose()
{
_bitmap?.Dispose();
_bitmap= null;
_activity = null;
_view = null;
_callback = null;
base.Dispose();
}
}

In your View you could run the following code which will take a screenshot. I have not tried running it in OnCreate() before so you may need to test that out to make sure the view has been fully rendered.
*Edit: According to this post you may have trouble running this code in OnCreate() so you will need to find a better place. I was unable to figure out what post the user was referring to in the link he posted.
*Edit #2: Just found out that Compress() does not take the quality parameter (which is listed as 0 below) into account since PNG is lossless, but if you change the format to JPEG for example, then you may want to turn up the quality parameter since your image will look like garbage.
public byte[] SaveImage() {
DrawingCacheEnabled = true; //Enable cache for the next method below
Bitmap bitmap = GetDrawingCache(true); //Gets the image from the cache
byte[] bitmapData;
using(MemoryStream stream = new MemoryStream()) {
bitmap.Compress(Bitmap.CompressFormat.Png, 0, stream);
bitmapData = stream.ToArray();
}
return bitmapData;
}

Delete an image being used by another process

I am writing a winform application in C# to open an image and overlay another image on top of it.
The bottom image is a .jpg and the top one is a .bmp converted from .svg. The .jpg and the .svg are the only ones I want to keep in the folder. The .bmp works as a temp.
I was using the following code to overlay the images. But I am having trouble to delete the temp .bmp as it is used by another process. I think it is this combine code still have access to the last .bmp file.
Could anyone help me on this? Thanks.
private void buttonSearch_Click(object sender, EventArgs e)
{
FailInfo.Text = "";
deletebmp(strFolderPath);
...
// Check if the specified front image exists. Yes, show the file name and convert SVG to BMP. No, show the error msg.
if (File.Exists(strFilePathF))
{
labelFront.Text = strFileNameF;
var svgConvert = SvgDocument.Open(svgFilePathF);
svgConvert.Draw().Save(bmpFilePathF);
pictureBoxFront.Image = Image.FromFile(strFilePathF);
}
else
{
labelFront.Text = "Couldn't find the file!";
pictureBoxFront.Image = null;
}
// Check if the specified back image exists. Yes, show the file name and convert SVG to BMP. No, show the error msg.
if (File.Exists(strFilePathBF))
{
labelBack.Text = strFileNameBF;
strFilePathB = strFilePathBF;
pictureBoxBack.Image = Image.FromFile(strFilePathB);
labelResult.Text = "FAIL";
labelResult.BackColor = Color.FromArgb(255, 0, 0);
var svgConvert = SvgDocument.Open(svgFilePathBF);
bmpFilePathB = strFolderPath + strFileNameBF + ".bmp";
svgConvert.Draw().Save(bmpFilePathB);
svgFilePathB = svgFilePathBF;
inspectionres(svgFilePathB);
labelreason.Visible = true;
}
else if (File.Exists(strFilePathBP))
{
labelBack.Text = strFileNameBP;
strFilePathB = strFilePathBP;
pictureBoxBack.Image = Image.FromFile(strFilePathB);
labelResult.Text = "PASS";
labelResult.BackColor = Color.FromArgb(0, 255, 0);
var svgConvert = SvgDocument.Open(svgFilePathBP);
bmpFilePathB = strFolderPath + strFileNameBP + ".bmp";
svgConvert.Draw().Save(bmpFilePathB);
svgFilePathB = svgFilePathBP;
inspectionres(svgFilePathB);
labelreason.Visible = false;
}
else
{
labelBack.Text = "Couldn't find the file!";
pictureBoxBack.Image = null;
labelResult.Text = "ERROR";
labelResult.BackColor = Color.FromArgb(0, 255, 255);
labelreason.Visible = false;
}
}
//
// Overlay the SVG file on top of the JPEG file
//
private Bitmap Combine(string jpegFile, string bmpFile)
{
Image image1 = Image.FromFile(jpegFile);
Image image2 = Image.FromFile(bmpFile);
Bitmap temp = new Bitmap(image1.Width, image1.Height);
using (Graphics g = Graphics.FromImage(temp))
{
g.DrawImageUnscaled(image1, 0, 0);
g.DrawImageUnscaled(image2, 0, 0);
}
return temp;
}
//
// Show the overlaid graphic in the picturebox
//
private void checkBoxOverlay_CheckedChanged(object sender, EventArgs e)
{
try
{
if (FindFront)
if (checkBoxOverlay.Checked)
pictureBoxFront.Image = Combine(strFilePathF, bmpFilePathF);
else
pictureBoxFront.Image = Image.FromFile(strFilePathF);
else
pictureBoxFront.Image = null;
if (FindBack)
if (checkBoxOverlay.Checked)
pictureBoxBack.Image = Combine(strFilePathB, bmpFilePathB);
else
pictureBoxBack.Image = Image.FromFile(strFilePathB);
else
pictureBoxBack.Image = null;
}
catch (Exception ex)
{
MessageBox.Show("Error loading image" + ex.Message);
}
}
//
// Option of changing the image folder
//
private void buttonPath_Click(object sender, EventArgs e)
{
FolderBrowserDialog FolderBrowserDialog1 = new FolderBrowserDialog();
if (FolderBrowserDialog1.ShowDialog() == DialogResult.OK)
{
strFolderPath = FolderBrowserDialog1.SelectedPath + "\\";
}
}
//
// Pull the inspection result info from the SVG file
//
private void inspectionres(string filename)
{
XDocument document = XDocument.Load(filename);
XElement svg_Element = document.Root;
string sb = null;
var faillist = (from svg_path in svg_Element.Descendants("{http://www.w3.org/2000/svg}text") select svg_path).ToList();
foreach (var item in faillist)
{
sb += item.ToString();
}
}
//
// Delete all the .bmp files generated from .svg files
//
private void deletebmp(string path)
{
// Unload the images from the picturebox if applicable
pictureBoxFront.Image = null;
pictureBoxBack.Image = null;
string[] files = Directory.GetFiles(path, "*.bmp");
for (int i = 0; i < files.Length; i ++ )
File.Delete(files[i]);
}
}

Image implements IDisposable, so simply setting the pictureBox.Image property to null will not release resources (in your case, the file). Your Combine method also leaves the images open. You have to call Dispose before attempting to delete the file:
Image image1 = Image.FromFile(path1);
File.Delete(path1); // error - file is locked
Image image2 = Image.FromFile(path2);
image2.Dispose();
File.Delete(path2); // works
An alternative approach (and I assume you're using WinForms here, in WPF it's a little different) would be to load the bitmap from the file manually (using FromStream). Then, you can close the stream immediately and delete the file:
Image image;
using (Stream stream = File.OpenRead(path))
{
image = System.Drawing.Image.FromStream(stream);
}
pictureBox.Image = image;
File.Delete("e:\\temp\\copy1.png"); //works

Vesan's answer didn't helped me so I found an different solution.
So I can safe/open an image and if I want instantly delete the image.
i used it for my dataGridView_SelectionChanged:
private void dataGridViewAnzeige_SelectionChanged(object sender, EventArgs e)
{
var imageAsByteArray = File.ReadAllBytes(path);
pictureBox1.Image = byteArrayToImage(imageAsByteArray);
}
public Image byteArrayToImage(byte[] byteArrayIn)
{
MemoryStream ms = new MemoryStream(byteArrayIn);
Image returnImage = Image.FromStream(ms);
return returnImage;
}

All above answers are perfectly fine, but I've got a different approach.
Using Image abstract class, you will not get quite a lot of options for manipulating and resizing image.
Rather you do as follows:-
Bitmap img = new Bitmap(item);
img.SetResolution(100, 100);
Image imgNew = Image.FromHbitmap(img.GetHbitmap());
pictureBox1.Image = imgNew;
img.Dispose();

Aforge.NET Webcam Control XAML page

I want to use a webcam in c# code with Aforge.NET, but It didin't work because I don't use forms.
See my code below :
public partial class CapturePage : Page
{
private bool DeviceExist = false;
private FilterInfoCollection videoDevices;
private VideoCaptureDevice videoSource = null;
public CapturePage()
{
InitializeComponent();
getCamList();
startVideo();
}
// get the devices name
private void getCamList()
{
try
{
videoDevices = new FilterInfoCollection(FilterCategory.VideoInputDevice);
if (videoDevices.Count == 0)
throw new ApplicationException();
DeviceExist = true;
}
catch (ApplicationException)
{
DeviceExist = false;
}
}
//toggle start and stop button
private void startVideo() // as it's say
{
if (DeviceExist)
{
videoSource = new VideoCaptureDevice(videoDevices[0].MonikerString); // the only one webcam
videoSource.NewFrame += new NewFrameEventHandler(video_NewFrame);
CloseVideoSource();
// videoSource.DesiredFrameSize = new Size(160, 120); // deprecated ?
//videoSource.DesiredFrameRate = 10;
videoSource.Start();
}
else
{
// error
}
}
else
{
if (videoSource.IsRunning)
{
timer1.Enabled = false;
CloseVideoSource();
}
}
}
//eventhandler if new frame is ready
private void video_NewFrame(object sender, NewFrameEventArgs eventArgs)
{
Bitmap img = (Bitmap)eventArgs.Frame.Clone();
//do processing here
pictureBox1.Image = img; // But I can't have pictureBox in xaml ??
}
//close the device safely
private void CloseVideoSource()
{
if (!(videoSource == null))
if (videoSource.IsRunning)
{
videoSource.SignalToStop();
videoSource = null;
}
}
}
}
I tried this code in a form application, and it's work, but with a page, PictureBox are not referenced. Even if I reference it and create one in the code, this didn't work.
Can I, and how, use a PictureBox in a XAML Page ? Or there is an other solution tu use Aforge.net Webcam in Xaml Page ?

I succeded with changing the NewFrame methode like this:
private void video_NewFrame(object sender, NewFrameEventArgs eventArgs)
{
System.Drawing.Image imgforms = (System.Drawing.Bitmap)eventArgs.Frame.Clone();
BitmapImage bi = new BitmapImage();
bi.BeginInit();
MemoryStream ms = new MemoryStream();
imgforms.Save(ms, ImageFormat.Bmp);
ms.Seek(0, SeekOrigin.Begin);
bi.StreamSource = ms;
bi.EndInit();
//Using the freeze function to avoid cross thread operations
bi.Freeze();
//Calling the UI thread using the Dispatcher to update the 'Image' WPF control
Dispatcher.BeginInvoke(new ThreadStart(delegate
{
ImageWebcam.Source = bi; /*frameholder is the name of the 'Image' WPF control*/
}));
}
cheers !

You could use WindowsFormsHost to integrate this Page in your WPF application.
If you need a WPF bitmap you may "convert" it like desribed here: Load a WPF BitmapImage from a System.Drawing.Bitmap

A generic error occurred in GDI When Saveing image in Database

I've uploaded my web form application on my host. in a part of my application, i try to save the image and int's thumbnail in sql server database. the data type of fields im using to save is varbinary(max). when I test the application on my computer. it works good but after uploading I got this error when trying to save the image in database.
The code I've written is like this:
NowbakhtEntities entities = new NowbakhtEntities();
protected void Page_Load(object sender, EventArgs e)
{
}
protected void btnInsert_Click(object sender, EventArgs e)
{
if (ImageUpload.HasFile)
{
Byte[] contents = ImageUpload.FileBytes;
MemoryStream imgStream = new MemoryStream(contents);
Byte[] thumb = null;
System.Drawing.Image img1 = new Bitmap(imgStream);
if (img1.Height < img1.Width)
{
int x = Convert.ToInt32((150*img1.Height)/img1.Width);
System.Drawing.Image bmp2 = img1.GetThumbnailImage(150, x, null, IntPtr.Zero);
thumb = ImageToByte(bmp2);
bmp2.Dispose();
}
else
{
int x = Convert.ToInt32((150*img1.Width)/img1.Height);
System.Drawing.Image bmp2 = img1.GetThumbnailImage(x, 150, null, IntPtr.Zero);
thumb = ImageToByte(bmp2);
bmp2.Dispose();
}
Project project = new Project();
project.Title = txtTitle.Text;
project.Description = txtDesc.Content;
project.Image = contents;
project.Thumb = thumb;
entities.Projects.Add(project);
entities.SaveChanges();
img1.Dispose();
imgStream.Close();
Response.Redirect("ProjectList.aspx");
}
}
public byte[] ImageToByte(System.Drawing.Image img)
{
ImageConverter converter = new ImageConverter();
return (byte[])converter.ConvertTo(img, typeof(byte[]));
}

How to pass a photo between pages in Windows Phone?

I know how to pass data through
NavigationService.Navigate(new Uri("/Second.xaml?msg=mesage", UriKind.Relative));
The question is, how can I pass an image selected from the library to another page?
To select an image, I use the PhotoChooserTask and in the event where it is completed I have this:
private void photoChooserTask_Completed(object sender, PhotoResult e)
{
if (e.ChosenPhoto != null)
{
BitmapImage image = new BitmapImage();
image.SetSource(e.ChosenPhoto);
this.img.Source = image;
}
}
How can I send the chosen photo to another page? Do I have to write it in a buffer, set a global variable or 'save' it in Isolated storage?

You could save your picture in IsolatedStorage first, pass the file path to another page as a string parameter, load the picture out when you need it.
Use PhoneApplicationService to save the image into State, load it when you need it.
Sample for saving into IsolatedStorage:
public static void SaveStreamToStorage(Stream imgStream, string fileName)
{
using (IsolatedStorageFile iso_storage = IsolatedStorageFile.GetUserStoreForApplication())
{
//Structure the path you want for your file.
string filePath = GetImageStorePathByFileName(fileName);
//Constants.S_STORE_PATH is the path I want to store my picture.
if (!iso_storage.DirectoryExists(Constants.S_STORE_PATH))
{
iso_storage.CreateDirectory(Constants.S_STORE_PATH);
}
//I skip the process when I find the same file.
if (iso_storage.FileExists(filePath))
{
return;
}
try
{
if (imgStream.Length > 0)
{
using (IsolatedStorageFileStream isostream = iso_storage.CreateFile(filePath))
{
BitmapImage bitmap = new BitmapImage();
bitmap.SetSource(imgStream);
WriteableBitmap wb = new WriteableBitmap(bitmap);
// Encode WriteableBitmap object to a JPEG stream.
Extensions.SaveJpeg(wb, isostream, wb.PixelWidth, wb.PixelHeight, 0, 100);
isostream.Close();
bitmap.UriSource = null;
bitmap = null;
wb = null;
}
}
}
catch(Exception e)
{
if (iso_storage.FileExists(filePath))
iso_storage.DeleteFile(filePath);
throw e;
}
}
}
Sample for reading picture from IsolatedStorage:
public static BitmapImage LoadImageFromIsolatedStorage(string imgName)
{
try
{
var bitmapImage = new BitmapImage();
//bitmapImage.CreateOptions = BitmapCreateOptions.DelayCreation;
using (var iso = IsolatedStorageFile.GetUserStoreForApplication())
{
//Check if file exists to prevent exception when trying to access the file.
if (!iso.FileExists(GetImageStorePathByFileName(imgName)))
{
return null;
}
//Since I store my picture under a folder structure, I wrote a method GetImageStorePathByFileName(string fileName) to get the correct path.
using (var stream = iso.OpenFile(GetImageStorePathByFileName(imgName), FileMode.Open, FileAccess.Read))
{
bitmapImage.SetSource(stream);
}
}
//Return the picture as a bitmapImage
return bitmapImage;
}
catch (Exception e)
{
// handle the exception
Debug.WriteLine(e.Message);
}
return null;
}

You could use a variable defined in your app.xaml.cs and call it from your other page like so (don't mind the variable names, just a code sample I use for language support):
private LanguageSingleton LanguageInstance
{
get
{
return (App.Current as App).Language;
}
}
Here is how you could define that variable:
public LanguageSingleton Language { get; set; }
I'm sure there are more ways in doing this but this is one solution.