harmony 鸿蒙<canvas> Development

2022-08-09
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<canvas> Development

The <canvas> component provides a canvas for drawing customized graphics. For details, see canvas.

Creating a <canvas> Component

Create a <canvas> component in the .hml file under pages/index.

<!-- xxx.hml -->
<div class="container">
  <canvas></canvas>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
}
canvas{
  background-color: #00ff73;
}

en-us_image_0000001232162316

NOTE

The default background color of the <canvas> component is the same as that of the parent component.

The default width and height of <canvas> are 300 px and 150 px, respectively.

Adding Styles

Set width, height, background-color, and border of the <canvas> component.

<!-- xxx.hml -->
<div class="container">
  <canvas></canvas>
</div>

/* xxx.css */
.container{
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
  width: 100%;
  height: 100%;
}
canvas{
  width: 500px;
  height: 500px;  
  background-color: #fdfdfd;  
  border: 5px solid red;
}

en-us_image_0000001231843104

Adding Events

Add the long press event to the <canvas> component. When the event is triggered, the value of dataUrl (image information returned by the toDataURL method) of the <canvas> component can be obtained and printed in the text area below.

<!-- xxx.hml -->
<div class="container">
  <canvas ref="canvas1" onlongpress="getUrl"></canvas>
  <text>dataURL</text>
  <text class="content">{{dataURL}}</text>
</div>

/* xxx.css */
.container{
  width:100%;
  height:100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
  }
  canvas{  
    width: 500px;  
    height: 500px;
    background-color: #fdfdfd;
    border: 5px solid red;
    margin-bottom: 50px;
}
.content{
  border: 5px solid blue;
  padding: 10px;
  width: 90%;
  height: 400px; 
  overflow: scroll;
}

// xxx.js
import promptAction from '@ohos.promptAction';
export default {
  data:{
    dataURL:null,
  },
  onShow(){
    let el = this.$refs.canvas1;
    let ctx = el.getContext("2d"); 
    ctx.strokeRect(100,100,300,300);
  },
  getUrl(){
    let el = this.$refs.canvas1
    let dataUrl = el.toDataURL()
    this.dataURL = dataUrl;
    promptAction.showToast({duration:2000,message:"long press,get dataURL"})
  }
}

en-us_image_0000001276003513