入门android ，至少需要了解 adb 吧，那么打 log 也是必不可少的了。
下面简单介绍一下 adb logcat 基本用法：
Usage: logcat [options] [filterspecs]
options include:
-s Set default filter to silent.
Like specifying filterspec '*:s'
-f <filename> Log to file. Default to stdout
-r [<kbytes>] Rotate log every kbytes. (16 if unspecified). Requires -f
-n <count> Sets max number of rotated logs to <count>, default 4
-v <format> Sets the log print format, where <format> is one of:
brief process tag thread raw time threadtime long
-c clear (flush) the entire log and exit
-d dump the log and then exit (don't block)
-t <count> print only the most recent <count> lines (implies -d)
-g get the size of the log's ring buffer and exit
-b <buffer> Request alternate ring buffer, 'main', 'system', 'radio'
or 'events'. Multiple -b parameters are allowed and the
results are interleaved. The default is -b main -b system.
-B output the log in binary
filterspecs are a series of
<tag>[:priority]
where <tag> is a log component tag (or * for all) and priority is:
V Verbose
D Debug
I Info
W Warn
E Error
F Fatal
S Silent (supress all output)
'*' means '*:d' and <tag> by itself means <tag>:v
If not specified on the commandline, filterspec is set from ANDROID_LOG_TAGS.
If no filterspec is found, filter defaults to '*:I'
If not specified with -v, format is set from ANDROID_PRINTF_LOG
or defaults to "brief"
实例：adb logcat -v time -s videocamera
意思是说，会打印出 log 信息中时间，以及包含关键字 "videocamera" 的所有 log
C:UsersAdministrator>adb logcat -v time -s videocamera fulin
--------- beginning of /dev/log/system
--------- beginning of /dev/log/main
07-01 08:43:57.037 V/videocamera( 2329): VideoCamera onCreate!
07-01 08:43:57.039 I/videocamera( 2329): getExternalSdState() : removed
07-01 08:43:57.040 I/videocamera( 2329): getExternalState() : mounted
07-01 08:43:57.040 I/videocamera( 2329): Sdcard is exists ? false
07-01 08:43:57.157 V/videocamera( 2329): fulin onCreate Storage.getAvailableSpace() 1335459840
07-01 08:43:57.159 V/videocamera( 2329): fulin initThumbnailButton
07-01 08:43:57.170 D/videocamera( 2329): Thumbnail.getLastThumbnail >>>
07-01 08:43:57.204 E/videocamera( 2329): --------------readVideoPreferences---------------minutes = 600
07-01 08:43:57.205 E/videocamera( 2329): --------------readVideoPreferences----------quality6=10
07-01 08:43:57.207 E/videocamera( 2329): -----------------readVideoPreferences---------mCameraId=0
07-01 08:43:57.208 E/videocamera( 2329): -----------------readVideoPreferences---------quality7=10
07-01 08:43:57.209 V/videocamera( 2329): mDesiredPreviewWidth=640. mDesiredPreviewHeight=480
07-01 08:43:57.234 V/videocamera( 2329): startPreview
07-01 08:43:57.240 V/videocamera( 2329): videocamera--mParameters.setFocusMode(mFocusManager.getFocusMode())
07-01 08:43:57.265 D/videocamera( 2329): Thumbnail.getLastThumbnail <<< is null:false
07-01 08:43:57.269 V/videocamera( 2329): Video snapshot size is 3264x2448
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 176x144
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 320x240
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 352x288
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 480x368
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 640x480
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 720x480
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 800x600
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 864x480
07-01 08:43:57.376 D/videocamera( 2329): SupportedPreviewSizes : 1280x720
07-01 08:43:57.422 V/videocamera( 2329): updateSceneOnScreenIndicator isVisible falsemSceneIndicatorandroid.widget.ImageView@41acd0e0