ShellItemImages.GetImageAsync might throw NullReferenceException

[zhuxb711]

Describe the bug and how to reproduce

Recently, I got some stacktrace and found that ShellItemImages.GetImageAsync might throw NRE.

Although the stacktrace do not show any useful information, but I think this issue might be related to the ShellItem.Parent. ShellItem.Parent might return null.

Vanara/Windows.Shell.Common/ShellObjects/ShellItemImages.cs

Lines 50 to 64 in f66686c

	if (hr != HRESULT.S_OK && !flags.IsFlagSet(ShellItemGetImageOptions.IconOnly))
	hr = LoadImageFromExtractImage(shellItem.Parent.IShellFolder, shellItem.PIDL.LastId, ref sz, out hbmp);
	if (hr != HRESULT.S_OK)
	{
	if (!flags.IsFlagSet(ShellItemGetImageOptions.ThumbnailOnly))
	{
	LoadIconFromExtractIcon(shellItem.Parent.IShellFolder, shellItem.PIDL.LastId, ref sz, out SafeHICON hIcon).ThrowIfFailed();
	using (hIcon)
	hbmp = hIcon.ToHBITMAP();
	}
	else
	{
	throw hr.GetException();
	}
	}

Vanara/Windows.Shell.Common/ShellObjects/ShellItem.cs

Lines 502 to 509 in f66686c

	public ShellFolder Parent
	{
	get
	{
	try { return new ShellFolder(iShellItem.GetParent()); } catch { }
	return null;
	}
	}

What code is involved

using (ShellItem Item = new ShellItem("<Your path>"))
using (Gdi32.SafeHBITMAP HBitmap = Item.GetImage(new SIZE(150, 150), ShellItemGetImageOptions.BiggerSizeOk))
{

}

Expected behavior
Should not throw NullReferenceException

By the way, it would be better to call the sync function directly rather than wait for Task.Result here, you simply warp the function in Task.Run()

Vanara/Windows.Shell.Common/ShellObjects/ShellItem.cs

Line 699 in f66686c

public SafeHBITMAP GetImage(SIZE size, ShellItemGetImageOptions flags) => Images.GetImageAsync(size, flags).Result;

Vanara/Windows.Shell.Common/ShellObjects/ShellItemImages.cs

Line 30 in f66686c

public async Task<SafeHBITMAP> GetImageAsync(SIZE size, ShellItemGetImageOptions flags = 0, bool forcePreVista = false) => await TaskAgg.Run(() =>

[dahall]

I applied what I think is a fix for the NRE -- many more null checks. On your second point about wrapping the function in Task.Run, I don't see your request. Can you show how you'd do it for those two method calls?

[zhuxb711]

@dahall What I mean is that GetImage should not use Task internally. Let the caller to decide whether to warp it in the Task.Run

public SafeHBITMAP GetImage(SIZE size, ShellItemGetImageOptions flags) => Images.GetImage(size, flags); 

[dahall]

Done