device-clock-guide.md

# Development Guidelines on Clock Apps<a name="EN-US_TOPIC_0000001115417926"></a>

## Overview<a name="section11522349121115"></a>

This document describes how to quickly set up a development environment \(using the Hi3516D V300 development board\) and develop a clock app running on OpenHarmony. You can click  [here](https://gitee.com/openharmony/app_samples/tree/master/common/Clock)  to obtain the sample code.

The clock app displays the current time, as shown in the following figure.

**Figure  1**  Clock display effect<a name="fig7763172132019"></a>  


![](figures/clock.png)

## Preparations<a name="section6592121861218"></a>

Download and install DevEco Studio. For details, see the  [HUAWEI DevEco Studio User Guide](../../application-dev/quick-start/deveco-studio-user-guide-for-openharmony.md). 

## How to Develop<a name="section19901741111312"></a>

The Clock app displays the current time through a clock face and numbers.

As shown in  [Figure 1 Clock display effect](#fig7763172132019), the UI consists of two parts:

-   Clock face area: displays a dynamic analog clock whose hands rotate accurately.
-   Digital time area: displays the current time in numerals.

To build such an app, we can create a page that has a flexible layout with two rows vertically arranged. The development procedure is as follows:

1.  Add a root component  **<div\>**  to the  **.hml**  file. Note that each  **.hml**  file can contain only one root component. The sample code is as follows:

    ```
    <div class="container">
    </div>
    ```

    **class="container"**  indicates the style used by the component. The  **container**  is a style class defined in the  **index.css**  file.

    ```
    .container {     
        flex-direction: column;
        justify-content: center;
        align-items: center;
        width: 100%;
        height: 100%;
    }
    ```

    The height and width of the root component  **<div\>**  are set in the style class. Note that the height and width must be explicitly specified \(except for some components, such as  **<text\>**\). Otherwise, the component may fail to display. In the  **container**  style class, the  **flex-direction**  attribute is set to  **column**, which means that child components of  **<div\>**  are vertically arranged from top to bottom for implementing the flexible page layout.

2.  Implement clock hand rotation using the  **<stack\>**  component. The  **<stack\>**  component provides a stack container where child components are successively stacked and the latter one overwrites the previous one.

    Add a stack container to the root component. The sample code is as follows:

    ```
    <div class="container">    
        <stack class="stack">
            <image src="/common/clock_bg.png" class="clock-bg"></image> <!--Set the clock face image.-->
            <image src="/common/hour_hand.png" class="clock-hand"
                   style="transform : rotate({{ hour * 30 + minute / 2 }}deg);"></image> <!--Set the hour hand image. (hour * 30) indicates that the hour hand rotates 30 degrees every hour.  (minute / 2) indicates the rotation degrees per minute.-->
            <image src="/common/minute_hand.png" class="clock-hand"
                   style="transform : rotate({{ minute * 6 + second / 10 }}deg);"></image> <!--Set the minute hand image. (minute * 6) indicates that the minute hand rotates 6 degrees every minute. (second / 10) indicates the rotation degrees per second.-->
            <image src="/common/second_hand.png" class="clock-hand"
                   style="transform : rotate({{ second * 6 }}deg);"></image> <!--Set the second hand image. (second * 6) indicates that the second hand rotates 6 degrees per second.-->
       </stack>
    </div>
    ```

    **style="transform: rotate\(\{\{ second \* 6 \}\}deg\)**  sets the rotation event of a component.  **transform**  translates, rotates, or scales an image.  **rotate**  rotates an image. You can set an image to rotate around its x-axis or y-axis.

    Set attributes, such as the height, width, and position, of the stack component in the CSS file. The sample code is as follows:

    ```
    .stack {
        flex-direction: column;
        justify-content: center;
        align-items: center;
        width: 100%;
        height: 50%;
    }
    ```

    Set attributes, such as the height and width, of the clock-bg component in the CSS file. The sample code is as follows:

    ```
    .clock-bg {
        width: 80%;
        height: 80%;
        object-fit: scale-down;
    }
    ```

    Set attributes, such as the height and width of the hour, minute, and second hands, of the clock-hand component in the CSS file. The sample code is as follows:

    ```
    .clock-hand {
        width: 25%;
        height: 65%;
        object-fit: contain;
    }
    ```

    Add a timer in the  **index.js**  file to update the hour, minute, and second variables in real time so that the time can be automatically updated on the app UI. The sample code is as follows:

    ```
    export default {
        timer: undefined,
        // Define parameters.
        data: {
          hour: 0,   // Define hours.
          minute: 0, // Define minutes.
          second: 0  // Define seconds.
        },
        onInit () {
            this.updateTime();
            this.timer = setInterval(this.updateTime, 1000)// Set the timer to 1 second.
        },  
        updateTime: function () {       
            var nowTime = new Date()    
            this.hour = nowTime.getHours()    
            this.minute = nowTime.getMinutes()   
            this.second = nowTime.getSeconds()    
            if (this.hour < 10) {        
                this.hour = '0' + this.hour    
            }  
            if (this.minute < 10) {       
                this.minute = '0' + this.minute   
            }    
            if (this.second < 10) {      
                this.second = '0' + this.second   
            }
        },
    }
    ```

3.  Display the current time in numerals under the analog clock. Add the text component at the end of the root layout. The following example shows the UI structure:

    ```
    <text class="digit-clock"> {{ hour }}:{{ minute }}:{{ second }}</text>
    ```

    class=**"digit-clock"**  sets the height, width, and font size of the component. The sample code is as follows:

    ```
    .digit-clock {    
        font-size: 58px;   
        width: 100%;
        margin-top: 0px;
        text-align: center;
    }
    ```

4.  Set the style, animation effect, and dynamic data binding for all components. The complete sample code is as follows:
    -   **index.hml**

        ```
        <div class="container">
            <stack class="stack">
                <image src="/common/clock_bg.png" class="clock-bg"></image>
                <image src="/common/hour_hand.png" class="clock-hand"
                       style="transform : rotate({{ hour * 30 + minute / 2 }}deg);"></image>
                <image src="/common/minute_hand.png" class="clock-hand"
                       style="transform : rotate({{ minute * 6 + second / 10 }}deg);"></image>
                <image src="/common/second_hand.png" class="clock-hand"
                       style="transform : rotate({{ second * 6 }}deg);"></image>
            </stack>
            <text class="digit-clock">{{ hour }}:{{ minute }}:{{ second }}</text>
        </div>
        ```

    -   **index.css**

        ```
        .container {
            flex-direction: column;
            justify-content: center;
            align-items: center;
            width: 100%;
            height: 100%;
        }
        
        .stack {
            flex-direction: column;
            justify-content: center;
            align-items: center;
            width: 100%;
            height: 50%;
        }
        
        .digit-clock {
            font-size: 58px;
            width: 100%;
            margin-top: 0px;
            text-align: center;
        }
        
        .clock-bg {
            width: 80%;
            height: 80%;
            object-fit: scale-down;
        }
        
        .clock-hand {
            width: 25%;
            height: 65%;
            object-fit: contain;
        }
        ```

    -   **index.js**

        A  **.js**  file is used to implement logic interactions of the clock app. The following  **.js**  file implements the function of periodically obtaining the system time.

        ```
        export default {
            timer: undefined,
            data: {
                hour: 0,
                minute: 0,
                second: 0
            },
            onInit() {
                this.updateTime()
                this.timer = setInterval(this.updateTime, 1000)
            },
            updateTime: function () {
                var nowTime = new Date()
                this.hour = nowTime.getHours()
                this.minute = nowTime.getMinutes()
                this.second = nowTime.getSeconds()
                if (this.hour < 10) {
                    this.hour = '0' + this.hour
                }
                if (this.minute < 10) {
                    this.minute = '0' + this.minute
                }
                if (this.second < 10) {
                    this.second = '0' + this.second
                }
            },
            onDestroy() {
                clearInterval(this.timer);
            }
        }
        ```



## Signing and Packaging<a name="section10601181101516"></a>

After finishing writing the app code, you need to sign and package the app before running it on a real device. For details, see  [Signing and Packaging Guide](https://developer.harmonyos.com/en/docs/documentation/doc-guides/ohos-debugging-and-running-0000001263040487#section17660437768).

## Running on the Real Device<a name="section092721731511"></a>

Before you install the app and run it on the development board, install the DevEco Device Tool by following operations provided in  [HUAWEI DevEco Device Tool User Guide](https://device.harmonyos.com/en/docs/ide/user-guides/service_introduction-0000001050166905). Burn OpenHarmony into the development board, and run it on the board. For details about how to build, burn, and run an image, see . After the image is running normally and the system is started properly, perform the following steps to install or uninstall the app:

1.  Obtain the HDC client from the following path:

    ```
    developtools/hdc_standard/prebuilt/windows/hdc_std.exe
    ```

    Change the HDC client name to  **hdc.exe**  and add the path above to the system environment variable  **path**.

2.  Open the  **cmd**  window, and run the following commands to push the HAP file to the device directory, and install it:

    ```
    hdc install clock.hap
    ```

3.  Run the following command to start the app.  **ohos.samples.clock**  indicates the app package name, and  **MainAbility**  indicates the ability started by the app.

    ```
    hdc shell aa start -d 123 -a ohos.samples.clock.MainAbility -b ohos.samples.clock
    ```

4.  \(Optional\) Run the following command to uninstall the app.  **ohos.samples.clock**  indicates the app package name.

    ```
    hdc shell bm uninstall -n ohos.samples.clock
    ```


## FAQs<a name="section1122413460153"></a>

### hdc\_std Fails to Connect to a Device<a name="section1922725151614"></a>

-   **Symptom**

    **\[Empty\]**  is displayed in the output after the  **hdc\_std list targets**  command is run.

-   **Possible Causes and Solutions**
    1.  The device fails to be identified.

        Check whether  **HDC Device**  exists in the universal serial bus device of the device manager. If  **HDC Device**  does not exist, the device cannot be connected. In this case, remove and then insert the device or burn the latest image for the device.

    2.  hdc\_std works improperly.

        Run the  **hdc kill**  or  **hdc start -r**  command to kill or restart the HDC service, and then run the  **hdc list targets**  command to check whether device information is obtained.

    3.  hdc\_std does not match the device.

        If the latest image is burnt for the device, hdc\_std must also be of the latest version. As hdc\_std is updated continuously, obtain hdc\_std of the latest version from the  **developtools\_hdc\_standard**  repository in the  **prebuilt**  directory.



### hdc\_std Fails to Run<a name="section15657547131615"></a>

-   **Symptom**

    The  **hdc\_std.exe**  file does not run after being clicked.

-   **Possible Causes and Solutions**

    **hdc\_std.exe**  requires no installation and can be directly used on a disk. It can also be added to environment variables. Open the  **cmd**  window and run the  **hdc\_std**  command to use  **hdc\_std.exe**.