Camera on Android Example

问题:

I want to write an activity that:

1. Shows the camera preview (viewfinder), and has a "capture" button.
2. When the "capture" button is pressed, takes a picture and returns it to the calling activity (setResult() & finish()).

Are there any complete examples out there that works on every device? A link to a simple open source application that takes pictures would be the ideal answer.

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My research so far:

This is a common scenario, and there are many questions and tutorials on this.

There are two main approaches:

1. Use the android.provider.MediaStore.ACTION_IMAGE_CAPTURE event. See this question
2. Use the Camera API directly. See this example or this question (with lots of references).

Approach 1 would have been perfect, but the issue is that the intent is implemented differently on each device. On some devices it works well. However, on some devices you can take a picture but it is never returned to your app. On some devices nothing happens when you launch the intent. Typically it also saves the picture to the SD card, and requires the SD card to be present. The user interaction is also different on every device.

With approach 2 the issues is stability. I tried some examples, but I've managed to stop the camera from working (until a restart) on some devices and completely freeze another device. On another device the capture worked, but the preview stayed black.

I would have used ZXing as an example application (I work with it a lot), but it only uses the preview (viewfinder), and doesn't take any pictures. I also found that on some devices, ZXing did not automatically adjust the white balance when the lighting conditions changed, while the native camera app did it properly (not sure if this can be fixed).

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Update:

For a while I used the camera API directly. This gives more control (custom UI, etc), but I would not recommend it to anyone. I would work on 90% of devices, but every now and again a new device would be released, with a different problem.

Some of the problems I've encountered:

• Handling autofocus
• Handling flash
• Supporting devices with a front camera, back camera or both
• Each device has a different combination of screen resolution, preview resolutions (doesn't always match the screen resolution) and picture resolutions.

So in general, I'd not recommend going this route at all, unless there is no other way. After two years I dumped by custom code and switched back to the Intent-based approach. Since then I've had much less trouble. The issues I've had with the Intent-based approach in the past was probably just my own incompetence.

If you really need to go this route, I've heard it's much easier if you only support devices with Android 4.0+.

回答1:

With approach 2 the issues is stability. I tried some examples, but I've managed to stop the camera from working (until a restart) on some devices and completely freeze another device. On another device the capture worked, but the preview stayed black.

Either there is a bug in the examples or there is a compatibility issue with the devices.

回答2:

The example that CommonsWare gave works well. The example works when using it as-is, but here are the issues I ran into when modifying it for my use case:

1. Never take a second picture before the first picture has completed, in other words PictureCallback.onPictureTaken() has been called. The CommonsWare example uses the inPreview flag for this purpose.
2. Make sure that your SurfaceView is full-screen. If you want a smaller preview you might need to change the preview size selection logic, otherwise the preview might not fit into the SurfaceView on some devices. Some devices only support a full-screen preview size, so keeping it full-screen is the simplest solution.

To add more components to the preview screen, FrameLayout works well in my experience. I started by using a LinearLayout to add text above the preview, but that broke rule #2. When using a FrameLayout to add components on top of the preview, you don't have any issues with the preview resolution.

I also posted a minor issue relating to Camera.open() on GitHub.

回答3:

"the recommended way to access the camera is to open Camera on a separate thread". Otherwise, Camera.open() can take a while and might bog down the UI thread.

"Callbacks will be invoked on the event thread open(int) was called from". That's why to achieve best performance with camera preview callbacks (e.g. to encode them in a low-latency video for live communication), I recommend to open camera in a new HandlerThread, as shown here.