Android调用camera错误setParameters failed深层解析

1. Camera

Camera是Android framework里面支持的，允许你拍照和拍摄视频的设备，那么，在使用camera开发中总是会遇到一些问题，例如以下这样子的：

E/AndroidRuntime(1542): java.lang.RuntimeException: setParameters failed
E/AndroidRuntime(1542):  at android.hardware.Camera.native_setParameters(Native Method)
E/AndroidRuntime(1542):  at android.hardware.Camera.setParameters(Camera.java:914)
出现这种错误，根据错误提示我们可以知道是android的setParameters方法出错了。

2、那该如何解决呢？

我们知道camera的parameters中也有很多参数设置的，是哪个出错了呢？很多人不知所以然就上网开始找，找不到就开始各种猜测，一个个参数设置过去，其实最有效的方式是到底层找原因。ok，让我们打开android代码找到camera类。然后查找setParameters方法。

 private native final void native_setParameters(String params);

    /**
     * Changes the settings for this Camera service.
     *
     * @param params the Parameters to use for this Camera service
     * @throws RuntimeException if any parameter is invalid or not supported.
     * @see #getParameters()
     */
    public void setParameters(Parameters params) {
        native_setParameters(params.flatten());
    }

从这段代码中代码中，我们可以得到什么信息呢，setParameters方法是调用jni方法native_setParameters的方法，其实看到这里就差并不多了，因为再去查看jni方法是很麻烦的，毕竟我们日常开发使用大部分是java代码。我们可以发现传输进来的是Parameters参数，调用了Parameters的flatten方法。我们查找flatten的代码进行查看。

 /**
         * Creates a single string with all the parameters set in
         * this Parameters object.
         * <p>The {@link #unflatten(String)} method does the reverse.</p>
         *
         * @return a String with all values from this Parameters object, in
         *         semi-colon delimited key-value pairs
         */
        public String flatten() {
            StringBuilder flattened = new StringBuilder();
            for (String k : mMap.keySet()) {
                flattened.append(k);
                flattened.append("=");
                flattened.append(mMap.get(k));
                flattened.append(";");
            }
            // chop off the extra semicolon at the end
            flattened.deleteCharAt(flattened.length()-1);
            return flattened.toString();
        }

从这段代码中，我们又能得到什么信息呢。我们可以看到提供数据的时候，数据都是从mMap中获取的。ok，接下来，我们查看一下mMap是有几个方法对其进行了赋值呢。

/**
         * Takes a flattened string of parameters and adds each one to
         * this Parameters object.
         * <p>The {@link #flatten()} method does the reverse.</p>
         *
         * @param flattened a String of parameters (key-value paired) that
         *                  are semi-colon delimited
         */
        public void unflatten(String flattened) {
            mMap.clear();

            StringTokenizer tokenizer = new StringTokenizer(flattened, ";");
            while (tokenizer.hasMoreElements()) {
                String kv = tokenizer.nextToken();
                int pos = kv.indexOf('=');
                if (pos == -1) {
                    continue;
                }
                String k = kv.substring(0, pos);
                String v = kv.substring(pos + 1);
                mMap.put(k, v);
            }
        }

        /**
         * Sets a String parameter.
         *
         * @param key   the key name for the parameter
         * @param value the String value of the parameter
         */
        public void set(String key, String value) {
            if (key.indexOf('=') != -1 || key.indexOf(';') != -1) {
                Log.e(TAG, "Key \"" + key + "\" contains invalid character (= or ;)");
                return;
            }
            if (value.indexOf('=') != -1 || value.indexOf(';') != -1) {
                Log.e(TAG, "Value \"" + value + "\" contains invalid character (= or ;)");
                return;
            }

            mMap.put(key, value);
        }

        /**
         * Sets an integer parameter.
         *
         * @param key   the key name for the parameter
         * @param value the int value of the parameter
         */
        public void set(String key, int value) {
            mMap.put(key, Integer.toString(value));
        }

        private void set(String key, List<Area> areas) {
            if (areas == null) {
                set(key, "(0,0,0,0,0)");
            } else {
                StringBuilder buffer = new StringBuilder();
                for (int i = 0; i < areas.size(); i++) {
                    Area area = areas.get(i);
                    Rect rect = area.rect;
                    buffer.append('(');
                    buffer.append(rect.left);
                    buffer.append(',');
                    buffer.append(rect.top);
                    buffer.append(',');
                    buffer.append(rect.right);
                    buffer.append(',');
                    buffer.append(rect.bottom);
                    buffer.append(',');
                    buffer.append(area.weight);
                    buffer.append(')');
                    if (i != areas.size() - 1) buffer.append(',');
                }
                set(key, buffer.toString());
            }
        }

        /**
         * Returns the value of a String parameter.
         *
         * @param key the key name for the parameter
         * @return the String value of the parameter
         */
        public String get(String key) {
            return mMap.get(key);
        }

        /**
         * Sets the dimensions for preview pictures. If the preview has already
         * started, applications should stop the preview first before changing
         * preview size.
         *
         * The sides of width and height are based on camera orientation. That
         * is, the preview size is the size before it is rotated by display
         * orientation. So applications need to consider the display orientation
         * while setting preview size. For example, suppose the camera supports
         * both 480x320 and 320x480 preview sizes. The application wants a 3:2
         * preview ratio. If the display orientation is set to 0 or 180, preview
         * size should be set to 480x320. If the display orientation is set to
         * 90 or 270, preview size should be set to 320x480. The display
         * orientation should also be considered while setting picture size and
         * thumbnail size.
         *
         * @param width  the width of the pictures, in pixels
         * @param height the height of the pictures, in pixels
         * @see #setDisplayOrientation(int)
         * @see #getCameraInfo(int, CameraInfo)
         * @see #setPictureSize(int, int)
         * @see #setJpegThumbnailSize(int, int)
         */
        public void setPreviewSize(int width, int height) {
            String v = Integer.toString(width) + "x" + Integer.toString(height);
            set(KEY_PREVIEW_SIZE, v);
        }

/**
         * <p>Sets the dimensions for EXIF thumbnail in Jpeg picture. If
         * applications set both width and height to 0, EXIF will not contain
         * thumbnail.</p>
         *
         * <p>Applications need to consider the display orientation. See {@link
         * #setPreviewSize(int,int)} for reference.</p>
         *
         * @param width  the width of the thumbnail, in pixels
         * @param height the height of the thumbnail, in pixels
         * @see #setPreviewSize(int,int)
         */
        public void setJpegThumbnailSize(int width, int height) {
            set(KEY_JPEG_THUMBNAIL_WIDTH, width);
            set(KEY_JPEG_THUMBNAIL_HEIGHT, height);
        }

      

        /**
         * Sets the quality of the EXIF thumbnail in Jpeg picture.
         *
         * @param quality the JPEG quality of the EXIF thumbnail. The range is 1
         *                to 100, with 100 being the best.
         */
        public void setJpegThumbnailQuality(int quality) {
            set(KEY_JPEG_THUMBNAIL_QUALITY, quality);
        }

     
        /**
         * Sets Jpeg quality of captured picture.
         *
         * @param quality the JPEG quality of captured picture. The range is 1
         *                to 100, with 100 being the best.
         */
        public void setJpegQuality(int quality) {
            set(KEY_JPEG_QUALITY, quality);
        }

      

        /**
         * Sets the rate at which preview frames are received. This is the
         * target frame rate. The actual frame rate depends on the driver.
         *
         * @param fps the frame rate (frames per second)
         * @deprecated replaced by {@link #setPreviewFpsRange(int,int)}
         */
        @Deprecated
        public void setPreviewFrameRate(int fps) {
            set(KEY_PREVIEW_FRAME_RATE, fps);
        }
       

        /**
         * Sets the maximum and maximum preview fps. This controls the rate of
         * preview frames received in {@link PreviewCallback}. The minimum and
         * maximum preview fps must be one of the elements from {@link
         * #getSupportedPreviewFpsRange}.
         *
         * @param min the minimum preview fps (scaled by 1000).
         * @param max the maximum preview fps (scaled by 1000).
         * @throws RuntimeException if fps range is invalid.
         * @see #setPreviewCallbackWithBuffer(Camera.PreviewCallback)
         * @see #getSupportedPreviewFpsRange()
         */
        public void setPreviewFpsRange(int min, int max) {
            set(KEY_PREVIEW_FPS_RANGE, "" + min + "," + max);
        }

       

       

        /**
         * Sets the image format for preview pictures.
         * <p>If this is never called, the default format will be
         * {@link android.graphics.ImageFormat#NV21}, which
         * uses the NV21 encoding format.</p>
         *
         * @param pixel_format the desired preview picture format, defined
         *   by one of the {@link android.graphics.ImageFormat} constants.
         *   (E.g., <var>ImageFormat.NV21</var> (default),
         *                      <var>ImageFormat.RGB_565</var>, or
         *                      <var>ImageFormat.JPEG</var>)
         * @see android.graphics.ImageFormat
         */
        public void setPreviewFormat(int pixel_format) {
            String s = cameraFormatForPixelFormat(pixel_format);
            if (s == null) {
                throw new IllegalArgumentException(
                        "Invalid pixel_format=" + pixel_format);
            }

            set(KEY_PREVIEW_FORMAT, s);
        }

    
       

        /**
         * <p>Sets the dimensions for pictures.</p>
         *
         * <p>Applications need to consider the display orientation. See {@link
         * #setPreviewSize(int,int)} for reference.</p>
         *
         * @param width  the width for pictures, in pixels
         * @param height the height for pictures, in pixels
         * @see #setPreviewSize(int,int)
         *
         */
        public void setPictureSize(int width, int height) {
            String v = Integer.toString(width) + "x" + Integer.toString(height);
            set(KEY_PICTURE_SIZE, v);
        }

   

        /**
         * Sets the image format for pictures.
         *
         * @param pixel_format the desired picture format
         *                     (<var>ImageFormat.NV21</var>,
         *                      <var>ImageFormat.RGB_565</var>, or
         *                      <var>ImageFormat.JPEG</var>)
         * @see android.graphics.ImageFormat
         */
        public void setPictureFormat(int pixel_format) {
            String s = cameraFormatForPixelFormat(pixel_format);
            if (s == null) {
                throw new IllegalArgumentException(
                        "Invalid pixel_format=" + pixel_format);
            }

            set(KEY_PICTURE_FORMAT, s);
        }

ok，错误的地方，我们就定位在这么几个地方了。在自己写的代码里面，查看一下是否调用了这几个方法~~~。android源码还是注释得比较清晰的，看看方法英文说明，看是否参数有出现了错误。

当时我的是使用setPictureSize时出现了错误，根据方法说明，我简单解释下，为什么会出错。因为parameters.setPictureSize(320, 480)(设置分辨率)的参数有误，如果不清楚分辨率可以却掉这句话，再运行就OK了。 

注：最后找了一下原因，感觉很简单，在实际 开发中，有时候一个小问题，就让人忙乎一个下午也是正常滴。