dotnet/wpf · error · IOException

Image_CannotCreateTempFile

Error message

Image_CannotCreateTempFile

What it means

BitmapDownload.BeginDownload attempted to create a temp file but every candidate path failed, so the download state machine cannot proceed and IOException(SR.Image_CannotCreateTempFile) is thrown. This is the aggregate failure after Win32Exception (1180) retries were exhausted or rethrown paths did not succeed.

Solutions

  1. Ensure %TEMP% exists and is writable by the process account
  2. Free disk space on the temp volume
  3. Fix corrupted TEMP/TMP environment variables
  4. Cache images locally and load from disk/streams instead of remote URIs

Example fix

// before
image.Source = new BitmapImage(new Uri(remoteUrl));
// after
string temp = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName() + ".img");
using (var wc = new WebClient()) wc.DownloadFile(remoteUrl, temp);
image.Source = new BitmapImage(new Uri(temp));
Defensive patterns

Strategy: try-catch

Validate before calling

bool canWriteTemp = Directory.Exists(Path.GetTempPath()) &&
    (from p in new[] { Path.GetTempPath() } select p).All(p =>
    { try { var f = Path.Combine(p, Guid.NewGuid().ToString()); using (File.Create(f)) { } File.Delete(f); return true; } catch { return false; } });

Try / catch

try { img.BeginInit(); img.UriSource = remoteUri; img.EndInit(); }
catch (IOException ex) when (ex.Message.Contains("temp") || ex is IOException) {
    log.Error("Image_CannotCreateTempFile", ex);
    img = LoadFromMemoryStream(DownloadToMemory(remoteUri)); }

Prevention

When it happens

Trigger: Downloading a bitmap from a URI via BitmapFrame/BitmapImage when the temp file cannot be created at any attempted location (invalid path characters in the generated name, denied ACLs, nonexistent temp directory, disk full).

Common situations: Misconfigured TEMP paths in services/IIS app pools, read-only system drives, group-policy folder redirection to unavailable network shares, disk space exhaustion.

Understand the failure class

Background: "open() failed", "failed to open file", "cannot create file" — what a file open error means and how to fix it — this error's family across 42 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ca03c4c1661ed54d. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/BitmapDownload.cs:168

                {
                    throw new Win32Exception();
                }
                    
                entry.outputStream = new FileStream(fileHandle, FileAccess.ReadWrite);
                entry.streamPath = pathToUse;
                passed = true;
            }
            catch(Exception e)
            {
                if (CriticalExceptions.IsCriticalException(e))
                {
                    throw;
                }
            }

            if (!passed)
            {
                throw new IOException(SR.Image_CannotCreateTempFile);
            }

            entry.readBuffer  = new byte[READ_SIZE];
            entry.contentLength = -1;
            entry.contentType = string.Empty;
            entry.lastPercent = 0;

            // Add the entry to the table if we know the uri
            if (uri != null)
            {
                lock (_syncLock)
                {
                    _uriTable[uri] = entry;
                }
            }

            if (stream == null)
            {

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