Camera.getParameters() 在 Galaxy Tab 上返回 null

Question

这是我的表面更改事件处理代码：

    public void surfaceChanged(SurfaceHolder holder,
                               int format, int width,
                               int height) {
    Camera.Parameters parameters = camera.getParameters();
    Camera.Size size = getBestPreviewSize(width, height,
                parameters);
       //...
    }


    private Camera.Size getBestPreviewSize(int width, int height,
                                       Camera.Parameters parameters) {
        Camera.Size result = null;

        // it fails with NullPointerExceptiopn here,
        // when accessing "getSupportedPreviewSizes" method:
        // that means "parameters" is null
        for (Camera.Size size : parameters.getSupportedPreviewSizes()) {
            ///...
        }
    }

我像这样初始化相机：

    @Override
    public void onResume() {
        super.onResume();
        camera = Camera.open();
    }

这个问题不会发生在我的 Galaxy S Plus 上，也不会发生在 LG Optimus Black 手机上。有人认为这里出了什么问题吗？

Answer 1

我已经解决了这个问题。

parameters.getSupportedPreviewSizes()

在 Galaxy Tab 上返回 NULL。因此，我只是检查它是否为空，并且在这种情况下不设置新的预览大小。我在研究了标准相机应用程序源之后得出了这个结论。

Answer 2

看起来相机变量从未初始化，因此您正在对 null 调用 getParameters() 。首先尝试调用camera = Camera.open();

Answer 3

相机初始化很大程度上取决于特定设备。例如，特定的三星设备 GT5500 报告空（宽度 = 0，高度 = 0）作为预览的有效分辨率，但如果您尝试使用它，则会导致整个手机崩溃（“硬”重启）。我们使用 mixare 增强现实引擎（http://www.mixare.org）体验了它，并且需要 PITA 进行调试（因为我们没有手机，无法在任何其他硬件上重现该错误）。

然而，关于获得“正确的”预览尺寸，您可以查看我们在 github 上的代码（它是一个免费的开源应用程序）。在文件中： https://github.com/mixare /mixare/blob/master/src/org/mixare/MixView.java（第 871 行及以后）

        List<Camera.Size> supportedSizes = null;
        //On older devices (<1.6) the following will fail
        //the camera will work nevertheless
        supportedSizes = Compatibility.getSupportedPreviewSizes(parameters);

        //preview form factor
        float ff = (float)w/h;
        Log.d("Mixare", "Screen res: w:"+ w + " h:" + h + " aspect ratio:" + ff);

        //holder for the best form factor and size
        float bff = 0;
        int bestw = 0;
        int besth = 0;
        Iterator<Camera.Size> itr = supportedSizes.iterator();

        //we look for the best preview size, it has to be the closest to the
        //screen form factor, and be less wide than the screen itself
        //the latter requirement is because the HTC Hero with update 2.1 will
        //report camera preview sizes larger than the screen, and it will fail
        //to initialize the camera
        //other devices could work with previews larger than the screen though
        while(itr.hasNext()) {
            Camera.Size element = itr.next();
            //current form factor
            float cff = (float)element.width/element.height;
            //check if the current element is a candidate to replace the best match so far
            //current form factor should be closer to the bff
            //preview width should be less than screen width
            //preview width should be more than current bestw
            //this combination will ensure that the highest resolution will win
            Log.d("Mixare", "Candidate camera element: w:"+ element.width + " h:" + element.height + " aspect ratio:" + cff);
            if ((ff-cff <= ff-bff) && (element.width <= w) && (element.width >= bestw)) {
                bff=cff;
                bestw = element.width;
                besth = element.height;
            }
        } 
        Log.d("Mixare", "Chosen camera element: w:"+ bestw + " h:" + besth + " aspect ratio:" + bff);
        //Some Samsung phones will end up with bestw and besth = 0 because their minimum preview size is bigger then the screen size.
        //In this case, we use the default values: 480x320
        if ((bestw == 0) || (besth == 0)){
            Log.d("Mixare", "Using default camera parameters!");
            bestw = 480;
            besth = 320;
        }
        parameters.setPreviewSize(bestw, besth);

如您所见，我们没有直接使用对 Camera 类的 getSupportedPreviewSizes 的调用，而是添加了一个兼容性层（代码在这里： https ://github.com/mixare/mixare/blob/master/src/org/mixare/Compatibility.java ）因为我们需要与旧手机兼容。如果您不想支持较旧的 Android 版本，您可以直接使用 Camera 类的方法。

华泰
丹尼尔