Android调用camera错误setParameters failed深层解析

朴灿烈づ我的快乐病毒、 2022-08-13 13:47 614阅读 0赞

## 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.
 * The {@link #unflatten(String)} method does the reverse.
 *
 * @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.
 * The {@link #flatten()} method does the reverse.
 *
 * @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);
 }

/**
 * Sets the dimensions for EXIF thumbnail in Jpeg picture. If
 * applications set both width and height to 0, EXIF will not contain
 * thumbnail.
 *
 * Applications need to consider the display orientation. See {@link
 * #setPreviewSize(int,int)} for reference.
 *
 * @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.
 * If this is never called, the default format will be
 * {@link android.graphics.ImageFormat#NV21}, which
 * uses the NV21 encoding format.
 *
 * @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);
 }
 
 
 
 
 /**
 * Sets the dimensions for pictures.
 *
 * Applications need to consider the display orientation. See {@link
 * #setPreviewSize(int,int)} for reference.
 *
 * @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。