> Programmer Feri is a programmer with 12 years of experience in development and leading the team to start businesses. He is good at Java, embedded, Hongmeng, artificial intelligence, etc. He focuses on the growth of programmers. I hope you will be with you on the road to growth! The will of your will, and move forward!
---
# 1. Preview + log debugging
This method can only print basic data types and is suitable for simple debugging
- Primitive types, that is, non-strings require String() or .toString()
- Object type, need to be converted
- Previewer - It's OK, emulator - Printing must be prefixed ** Otherwise, it won't be found **
Code example:
```
@Entry
@Component
struct Index {
//Record Number of clicks
@State cs: number = 1
build() {
Column() {
Text('Clicks=' + )
Button('Print Debug').onClick(() => {
++
// () An error? Why?
(())
(String())
// ({id:1,age:22}) An error?
(({ id: 1, age: 22 }))
// The emulator must be prefixed
('Feri ' + )
})
}
}
}
```
# 2. Breakpoint debugging
Taking the simulator as an example, the specific implementation steps are:
**Step 1: Encoding**
```
@Entry
@Component
struct Index {
@State message: string='Hello World'
build() {
Row(){
Column() {
Text()
.fontSize(50)
.fontWeight()
}
.width("100%")
}
.height("100%")
}
}
```
**Step 2: Break Point**
**Step 3: Click on the upper right corner to start debugging**
Click the Debug icon to start debugging. If your app is already running, click the Attach Debugger to Process icon!
When the application runs to the code, it stops at the code and is highlighted.
## Debug-related function key use
| **Button** | Name | **Function** | **Shortcut Keys** |
| ------------------------------------------------------------ | --------------- | ------------------------------------------------------------ | ---------------------------------------------- |
|
| Resume Program | When the program executes to a breakpoint, click this button to continue the program execution. | **F9** (macOS is **Option+Command+R**) |
| | Step Over | During step-by-step debugging, go directly to the next line (if a subfunction exists in the function, it will not enter the subfunction to execute in a single step, but will perform the entire subfunction as a one-step). | **F8** (macOS is **F8**) |
|
| Step Into | When stepping on debugging, after encountering the subfunction, enter the subfunction and continue to step-by-step execution. | **F7** (macOS is **F7**) |
|
| Force Step Into | Force entry into the method during step-by-step debugging. | **Alt+Shift+F7** (macOS is **Option+Shift+F7**) |
|
| Step Out | When stepping into a subfunction, clicking Step Out will execute the rest of the subfunction and jump out to return to the previous layer of function. | **Shift+F8** (macOS is **Shift+F8**) |
| | Stop | Stop the debugging task. | **Ctrl+F2** (macOS is **Command+F2**) |
|
| Run To Cursor | Breakpoint is executed to the mouse stop. | **Alt+F9** (macOS is **Option+F9**) |
#3 Hilog practical use
During application development, log information can be output at key code. After running the application, view the log information to analyze the application execution status (such as whether the application is running normally, the code run timing, whether the logic branch is running normally, etc.).
The system provides different APIs for developers to call and output log information, namely HiLog and console.
Hilog log prints up to 4096 bytes, and text exceeding the limit will be truncated.
The specific example code is as follows:
```
import { hilog } from '@';
@Entry
@Component
struct Index {
build() {
Column() {
Button('Print Debug').onClick(() => {
// Prepare 1: Hex (abbreviated as hex or subscript 16) is a counting system with a base of 16, and a carry system that goes to 1 every 16. Usually, the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and the letters A, B, C, D, E, F (a, b, c, d, e, f), where: A~F represents 10~15, these are called hexadecimal numbers.
// Prepare 2: Computer information is represented by 0 and 1, which is binary. For humans, binary is too long -> It needs to be simplified, so it is converted into hexadecimal.
// Prepare 3: In C language, hexadecimal numbers start with "0x" or "0X", A means 10, and F means 16.
// Prepare 4: From now on, 00000000~11111111 can be represented by 0x00~0xFF.
// The first parameter of the info function domain: used to specify the business field corresponding to the output log. The value range is 0x0000~0xFFFF, and developers can customize it as needed. For example, win blue screen code 0x00000ffff is an error code
// The first parameter of the info function tag: used to specify the log identifier, which can be any string. It is recommended to identify the class or business behavior where the call is located. The tag is up to 31 bytes, and it will be truncated after it is exceeded. It is not recommended to use Chinese characters, as there may be garbled code or alignment problems.
(0xFF00, "slj", 'hello');
})
}
}
}
```
It is relatively convenient to use when packaged and used in later maintenance
Practical recommendation @open/log
The sample code is as follows:
```
ohpm install @open/log
import log from '@open/log';
(data)
```
>Okay, that’s all for HarmonyOS NEXT development practical debugging skills.