Hongmeng hilog log printing tips

Preface ：

Hello everyone , There is no time to update the article for you , I don't know how long it will take . Recently, I still continue to learn about Hongmeng development . Usually developing Android or java as well as flutter You can use the log printing at the corresponding end to debug the code . Today, I'd like to share some tips on how to print Hongmeng's internal log .
## preparation ：
1 Install Hongmeng development environment You can see my previous article
Initial experience of Huawei Hongmeng system development ：[https://www.jianshu.com/p/f94c847c7fdc]

Log printing overview

HarmonyOS Provides HiLog Log system , So that the application can follow the specified type 、 Specify the level 、 Specify the format string to output the log content , Help developers understand the running status of applications , Better debugging programs .
The interface for outputting logs is provided by HiLog Class provides . Before outputting the log , You need to call HiLog Auxiliary class HiLogLabel Define log labels .

Define log labels

Use HiLogLabel(int type, int domain, String tag) Define log labels , This includes log types 、 Business areas and TAG. Examples of use ：

static final HiLogLabel LABEL = new HiLogLabel(HiLog.LOG_APP, 0x00201, "MY_TAG"); 

• Parameters type： Used to specify the type of output log .HiLog Currently, only one log type is provided in , That is, the application log type LOG_APP.
• Parameters domain： Used to specify the business domain corresponding to the output log , The value range is 0x0~0xFFFFF, Developers can customize as needed .
• Parameters tag： Used to specify the log id , Can be any string , It is recommended to identify the class or business behavior where the call is located .
  Developers can customize the parameters according to the domain and tag To filter and find logs .

Output log

HiLog It defines DEBUG、INFO、WARN、ERROR、FATAL Five log levels , Corresponding methods are provided to output different levels of logs , As shown in the following table .

• Parameters label： Defined HiLogLabel label .

• Parameters format： Format string , Formatted output for logs . Multiple parameters can be set in the format string , For example, the format string is “Failed to visit %s.”,“%s” The parameter type is string Variable parameter identification of , The specific value is args In the definition of .

  Each parameter needs to be added with a privacy id , It is divided into {public} or {private}, The default is {private}.{public} Indicates that the log print results are visible ;{private} Indicates that the log print result is not visible , The output is <private>.

• Parameters args： It can be for 0 Two or more parameters , Is the parameter list corresponding to the parameter type in the format string . Number of parameters 、 The type must correspond to the identity in the format string one by one .
  HiLog Source code

package ohos.hiviewdfx;public final class HiLog {    public static final int DEBUG = 3;    public static final int ERROR = 6;    public static final int FATAL = 7;    public static final int INFO = 4;    public static final int LOG_APP = 0;    public static final int WARN = 5;    HiLog() {        throw new RuntimeException("Stub!");    }    public static int debug(HiLogLabel label, String format, Object... args) {        throw new RuntimeException("Stub!");    }    public static int info(HiLogLabel label, String format, Object... args) {        throw new RuntimeException("Stub!");    }    public static int warn(HiLogLabel label, String format, Object... args) {        throw new RuntimeException("Stub!");    }    public static int error(HiLogLabel label, String format, Object... args) {        throw new RuntimeException("Stub!");    }    public static int fatal(HiLogLabel label, String format, Object... args) {        throw new RuntimeException("Stub!");    }    public static boolean isLoggable(int domain, String tag, int level) {        throw new RuntimeException("Stub!");    }    public static String getStackTrace(Throwable tr) {        throw new RuntimeException("Stub!");    }}

We used observation Hilog Source code Hilog Class provides the opposite method Yes

• debug

• info

• warn

• error

• fata

etc. 5 A static method
To output a WARN Level information as an example , Sample code ：

HiLog.warn(LABEL, "Failed to visit %{private}s, reason:%{public}d.", url, errno);

This line of code indicates that a log label is output label Warning message , The format string is ：“Failed to visit %{private}s, reason:%{public}d.”. Including variable parameters url The format of is a private string ,errno Is a public integer number .

View log information

DevEco Studio Provides HiLog Window to view log information , Developers can set up devices 、 process 、 Log level and search keywords to filter log information . The search function supports the use of regular expressions , Developers can search custom business domain values and TAG To filter log information .
As shown in the example , After selecting the equipment and process according to the actual situation , Search for business domain values “00201” Screening , Get the corresponding log information

Results output ：

01-20 16:08:36.908 23597-23597/com.example.myapplication W 00201/MY_TAG: Failed to visit <private>, reason:503

• W Indicates that the log level is WARN.
• 00201/MY_TAG For developers in HiLogLabel As defined in .
• In the log content url It is a private parameter and does not display the specific content , Show only <private>.errno Is a public parameter , Displays the actual value 503.

Log printing instance

• 1 Build a new project , stay “Project” Window click “entry > src > main > java > App package name > slice”, Open the “MainAbilitySlice.java” file , We are MainAbilitySlice Of onStart Method to print a log

package com.example.hms_logdemo.slice;import com.example.hms_logdemo.HiLogUtils;import com.example.hms_logdemo.ResourceTable;import ohos.aafwk.ability.AbilitySlice;import ohos.aafwk.content.Intent;import ohos.hiviewdfx.HiLog;import ohos.hiviewdfx.HiLogLabel;public class MainAbilitySlice extends AbilitySlice {    //  Define log labels     private static final HiLogLabel LABEL = new HiLogLabel(ohos.hiviewdfx.HiLog.LOG_APP, 0x00201, "HMS_TAG");    @Override    public void onStart(Intent intent) {        super.onStart(intent);        super.setUIContent(ResourceTable.Layout_ability_main);        HiLog.info(LABEL, "test");    }    @Override    public void onActive() {        super.onActive();    }    @Override    public void onForeground(Intent intent) {        super.onForeground(intent);    }}

• 2 Run the project , Click the button on the application interface .
• 3 stay DevEco Studio The bottom of , Switch to “HiLog” window , Set the log filter conditions .
  Select the current device and process , Log level selection Info, The search content is set to “00201” Or set the search content to "HMS_TAG". At this time, the window only displays the qualified logs , The effect is shown in the figure .

The effect is as shown in the picture ：

Log tool class

In actual development, we will write a tool class for the official log Make a proper package Edge banding we call And print log debugging

package com.example.hms_logdemo;import ohos.hiviewdfx.HiLog;import ohos.hiviewdfx.HiLogLabel;public class HiLogUtils {    public  static  final String  TAG="HMS_TAG";    private static final HiLogLabel LABEL = new HiLogLabel(ohos.hiviewdfx.HiLog.LOG_APP, 0x00201, TAG);    public static  boolean flag=false;    public  static  void  d(String msg){        if(!flag){            HiLog.debug(LABEL, msg);        }    }    public  static  void  e(String msg){        if(!flag){            HiLog.error(LABEL, msg);        }    }    public  static  void  w(String msg){        if(!flag){            HiLog.warn(LABEL, msg);        }    }    public  static  void i (String msg){        if(!flag){            HiLog.info(LABEL, msg);        }    }    public  static  oid  f(String msg){        if(!flag){            HiLog.fatal(LABEL, msg);        }    }}

Specific call

package com.example.hms_logdemo.slice;import com.example.hms_logdemo.HiLogUtils;import com.example.hms_logdemo.ResourceTable;import ohos.aafwk.ability.AbilitySlice;import ohos.aafwk.content.Intent;import ohos.hiviewdfx.HiLog;import ohos.hiviewdfx.HiLogLabel;public class MainAbilitySlice extends AbilitySlice {    @Override    public void onStart(Intent intent) {        super.onStart(intent);        super.setUIContent(ResourceTable.Layout_ability_main);        HiLog.info(LABEL, "test");        HiLogUtils.i("info");        HiLogUtils.e("test");        HiLogUtils.d("debug");        HiLogUtils.f("fatal");        HiLogUtils.w("warn");    }    @Override    public void onActive() {        super.onActive();    }    @Override    public void onForeground(Intent intent) {        super.onForeground(intent);    }}

Output effect

So far This is the end of Hongmeng's log printing skills .

The final summary

In fact, when we develop in actual combat , Because in config.json Configure key value pairs in the configuration file by reading Configuration file refers to To determine whether the log is enabled . our app On the go release It should be necessary to turn off our active printing log All we need to do is config.json Turn off the switch in the . The blog knowledge points in this issue are relatively simple Students should be able to understand and learn to use . Official documents also say I also do some sorting and add some personal opinions . Finally, I hope my article can help you to solve the problem , In the future, I will contribute more useful code to share with you . If you think the article is good , Please pay attention and star, Thank you here