相机setFocusAreas（）无法运行Android 4.0

Question

I'm creating a camera app that will use a tap to focus function, much like many of the standard camera apps come with. I first get the (x,y) coordinate of a touch event, then deliver this value to the UI. Then, I try to set the focus area, like this:

Rect newRect = new Rect(left,top,right, bottom);
Camera.Parameters params = mCamera.mCameraInstance.getParameters();
Camera.Area focusArea = new Camera.Area(newRect, 1000);
List<Camera.Area> focusAreas = new ArrayList<Camera.Area>();
focusAreas.add(focusArea);
params.setFocusAreas(focusAreas);

However, it appears to have no effect. So, I hardcoded some values into the rectangle (this way, I can rule out bad coordinates from the touch event). According to the docs , it is looking for a coordinate in the space (-1000, -1000)(upper left) to (1000, 1000)(bottom right).

So I replaced my rectangle above with this one:

//should target a 100x100 square in the center of the screen
Rect newRect = new Rect(-50,-50,50, 50);

And still, seems to have no effect. I know my camera supports setting focus areas, because first of all, the camera app uses it successfully, and also params.getMaxNumFocusAreas() returns 1.

If anyone has used this with success in the past, please let me know!!

Edit:

I found this similar question that seems to also indicate that this API simply doesn't work on Android 4.0 devices and up (im testing on 4.1.1, Galaxy S3). And yet, the camera apps on these devices still definitely has tap-to-focus functionality. What am I missing???

Answer 1

I had this problem today :/

And after hours of struggling, I found the solution!

It's strange, but it appears that setting focus-mode to "macro" right before setting focus-areas solved the problem ;)

params.setFocusMode(Camera.Parameters.FOCUS_MODE_MACRO);
params.setFocusAreas(focusAreas);
mCamera.setParameters(params);

I have Galaxy S3 with Android 4.1.2

I hope this will work for you either :)

Answer 2

It does not work for me neither, but anyways, when setting your rect, make sure that left < right and top < bottom ! Your are setting your rect to a height of -100! And, btw your not setting a square of 50x50 but 100x-100.

Answer 3

After perusing the source 4.3 source and staring at the Camera API for a few too many hours I found this function :

public final void autoFocus (Camera.AutoFocusCallback cb)

So you should be able to add a few lines to your code:

Rect newRect = new Rect(left,top,right, bottom);
Camera.Parameters params = mCamera.mCameraInstance.getParameters();
Camera.Area focusArea = new Camera.Area(newRect, 1000);
List<Camera.Area> focusAreas = new ArrayList<Camera.Area>();
focusAreas.add(focusArea);
params.setFocusAreas(focusAreas);

/**
 * ISO changes occurs passively after setting it in the cameraParams. Auto focus
 * parameters that have been set don't take affect until calling Camera.autoFocus()
 */
mCamera.autoFocus(new Camera.AutoFocusCallback()
{
    @Override
    public void onAutoFocus(boolean success, Camera camera)
    {
        Log.d(TAG, "onAutoFocus() " + success);
    }
});