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.
* 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 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., ImageFormat.NV21 (default),
* ImageFormat.RGB_565, or
* ImageFormat.JPEG)
* @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
* (ImageFormat.NV21,
* ImageFormat.RGB_565, or
* ImageFormat.JPEG)
* @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。