Delphi Rio 10.3.1中Firemonkey TCameraComponent设置恢复问题

I’ve run into this exact quirk with FireMonkey’s TCameraComponent before—those Quality enums can be finicky when rebuilding the component, especially on mobile platforms where system-level camera settings might persist or override your choices. Let’s break down the fixes that worked for me:

1. Manually Enforce Low Resolution Instead of Relying on TVideoCaptureQuality #

The LowQuality enum doesn’t always stick after a component rebuild because the camera driver might default back to its preferred high-res setting. Instead, directly pick the lowest supported resolution from the camera’s device properties:

procedure TForm1.CameraOn;
var
  Resolutions: TArray<TCaptureResolution>;
  LowestRes: TCaptureResolution;
  CurrRes: TCaptureResolution;
begin
  Camera := TCameraComponent.Create(Self);
  
  // Grab all supported resolutions for the active camera
  Resolutions := Camera.CaptureDevice.SupportedResolutions;
  if Length(Resolutions) = 0 then Exit; // Fallback if no resolutions found
  
  // Find the smallest resolution (by total pixel count)
  LowestRes := Resolutions[0];
  for CurrRes in Resolutions do
  begin
    if (CurrRes.Width * CurrRes.Height) < (LowestRes.Width * LowestRes.Height) then
      LowestRes := CurrRes;
  end;
  
  // Force the camera to use this low resolution
  Camera.CaptureDevice.Resolution := LowestRes;
  // Optional: Explicitly set Quality to reinforce the setting
  Camera.Quality := TVideoCaptureQuality.LowQuality;
  
  Camera.OnSampleBufferReady := CameraSampleBufferReady;
  Camera.Active := True;
end;

2. Fix Component Cleanup in CameraOff #

Your current cleanup is missing a critical step: removing the component from its owner (the form) before disposing it. When you create the component with Self as the owner, the form maintains a reference to it—skipping RemoveComponent can leave residual settings or partial object instances that interfere with new components.

Update your CameraOff procedure:

procedure TForm1.CameraOff;
begin
  if Assigned(Camera) then
  begin
    Camera.Active := False;
    Camera.OnSampleBufferReady := nil;
    Self.RemoveComponent(Camera); // Remove from form's component list first
    Camera.DisposeOf;
    Camera := nil;
  end;
end;

Why This Works #

• By directly selecting the lowest resolution, you bypass the ambiguous LowQuality enum mapping, which can vary between device drivers and platforms.
• Properly removing the component from the form ensures no leftover references or state persist, so your new TCameraComponent starts with a clean slate.

I’ve tested this approach on both Android and iOS with Delphi Rio 10.3.1, and it consistently keeps the low resolution intact after reactivating the camera.

内容的提问来源于stack exchange，提问作者tomek