Android SDK下, 如何在程序中输出日志 以及如何查看日志.

Android SDK下, 如何在程序中输出日志 以及如何查看日志.

闲话少说,直接进入正题


在程序中输出日志, 使用 android.util.Log 类.
该类提供了若干静态方法

Log.v(String tag, String msg);
Log.d(String tag, String msg);
Log.i(String tag, String msg);
Log.w(String tag, String msg);
Log.e(String tag, String msg);

分别对应 Verbose, Debug, Info, Warning,Error.

tag是一个标识,可以是任意字符串,通常可以使用类名+方法名, 主要是用来在查看日志时提供一个筛选条件.


程序运行后 并不会在 ide的控制台内输出任何信息.

如果要后查看日志 请使用

adb logcat

关于adb的更多信息请查看官方网站.

当执行 adb logcat 后会以tail方式实时显示出所有的日志信息.

这时候我们通常需要对信息进行过滤,来显示我们需要的信息, 这时候我们指定的 tag就派上了用场.

adb logcat -s MyAndroid:I

这时将只显示tag为MyAndroid,级别为I或级别高于I(Warning,Error)的日志信息.

示例代码如下:

 

1.package com.zijun;
2.
3.import android.app.Activity;
4.import android.content.Context;
5.import android.graphics.Canvas;
6.import android.os.Bundle;
7.import android.util.Log;
8.import android.view.MotionEvent;
9.import android.view.View;
10.
11.public class MyAndroid extends Activity {
12.
13. protected static final String ACTIVITY_TAG="MyAndroid";
14.
15. @Override
16. protected void onCreate(Bundle icicle) {
17. super.onCreate(icicle);
18. setContentView(new MyView(this));
19. }
20. public class MyView extends View {
21. public MyView(Context c) {
22. super(c);
23. }
24. @Override
25. protected void onDraw(Canvas canvas) {
26.
27. }
28. @Override
29. public boolean onMotionEvent(MotionEvent event) {
30. Log.i(MyAndroid.ACTIVITY_TAG, "=============================");
31.
32. Log.d(MyAndroid.ACTIVITY_TAG, "Haha , this is a DEBUG of MyAndroid. ");
33. Log.i(MyAndroid.ACTIVITY_TAG, "Haha , this is a INFO of MyAndroid. ");
34. Log.w(MyAndroid.ACTIVITY_TAG, "Haha , this is a WARNING of MyAndroid. ");
35.
36. return true;
37. }
38.
39. }
40.
41.}

以上程序运行后, 在命令行执行  adb logcat -s MyAndroid:I
然后在手机模拟器的屏幕上 点击 拖动鼠标 就能看到相应的日志信息.
附 logcat的参数说明

1.Usage: logcat [options] [filterspecs]
2.options include:
3. -s Set default filter to silent.
4. Like specifying filterspec '*:s'
5. -f <filename> Log to file. Default to stdout
6. -r [<kbytes>] Rotate log every kbytes. (16 if unspecified). Requires -f
7. -n <count> Sets max number of rotated logs to <count>, default 4
8. -v <format> Sets the log print format, where <format> is one of:
9.
10. brief process tag thread raw time long
11.
12. -c clear (flush) the entire log and exit
13. -d dump the log and then exit (don't block)
14. -g get the size of the log's ring buffer and exit
15. -b <buffer> request alternate ring buffer, defaults to 'main'
16.filterspecs are a series of
17. <tag>[:priority]
18.
19.where <tag> is a log component tag (or * for all) and priority is:
20. V Verbose
21. D Debug
22. I Info
23. W Warn
24. E Error
25. F Fatal
26. S Silent (supress all output)
27.
28.'*' means '*:d' and <tag> by itself means <tag>:v
29.
30.If not specified on the commandline, filterspec is set from ANDROID_LOG_TAG
31.If no filterspec is found, filter defaults to '*:I'
32.
33.If not specified with -v, format is set from ANDROID_PRINTF_LOG
34.or defaults to "brief"
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 long

  -c clear (flush) the entire log and exit
  -d dump the log and then exit (don't block)
  -g get the size of the log's ring buffer and exit
  -b <buffer> request alternate ring buffer, defaults to 'main'
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_TAG
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"