Android調用camera錯誤setParameters failed深層解析

1. Camera

Camera是Android framework裡面支持的,允許你拍照和拍攝視頻的設備,那麼,在使用camera開發中總是會遇到一些問題,例如以下這樣子的:

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)
出現這種錯誤,根據錯誤提示我們可以知道是android的setParameters方法出錯瞭。

2、那該如何解決呢?

我們知道camera的parameters中也有很多參數設置的,是哪個出錯瞭呢?很多人不知所以然就上網開始找,找不到就開始各種猜測,一個個參數設置過去,其實最有效的方式是到底層找原因。ok,讓我們打開android代碼找到camera類。然後查找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());
    }

從這段代碼中代碼中,我們可以得到什麼信息呢,setParameters方法是調用jni方法native_setParameters的方法,其實看到這裡就差並不多瞭,因為再去查看jni方法是很麻煩的,畢竟我們日常開發使用大部分是java代碼。我們可以發現傳輸進來的是Parameters參數,調用瞭Parameters的flatten方法。我們查找flatten的代碼進行查看。

 /**
         * 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(); }

從這段代碼中,我們又能得到什麼信息呢。我們可以看到提供數據的時候,數據都是從mMap中獲取的。ok,接下來,我們查看一下mMap是有幾個方法對其進行瞭賦值呢。

/**
         * 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,錯誤的地方,我們就定位在這麼幾個地方瞭。在自己寫的代碼裡面,查看一下是否調用瞭這幾個方法~~~。android源碼還是註釋得比較清晰的,看看方法英文說明,看是否參數有出現瞭錯誤。

當時我的是使用setPictureSize時出現瞭錯誤,根據方法說明,我簡單解釋下,為什麼會出錯。因為parameters.setPictureSize(320,
480)(設置分辨率)的參數有誤,如果不清楚分辨率可以卻掉這句話,再運行就OK瞭。

註:最後找瞭一下原因,感覺很簡單,在實際 開發中,有時候一個小問題,就讓人忙乎一個下午也是正常滴。

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