Angular6 - canvas.drawImage（）不起作用 [英] Angular6 - canvas.drawImage() not working

问题描述

我想把图片放在画布上。最初我用图像作为背景。但每当我将画布转换为图像时，背景图像都不会被复制。因此我试图在画布上绘制图像。我从设备图库中选择图像。将图像URL存储为字符串并传递给下一个组件。我检查过，能够得到价值。请看下面的代码，让我知道我做错了什么。

I want to put image on canvas. initially I used image as background. But whenever I convert canvas to image, background image is not getting copied. Hence I tried to draw image on canvas. I am choosing image from device image gallery. Storing the image url as string and passing to next component. I checked, able to get the value. Please see below code and let me know what I did wrong.

1。 HTML

<canvas no-bounce id="canvas"
    (touchstart)='handleStart($event)' (touchmove)='handleMove($event)' (touchend)='handleEnd($event)' (click)="removeSelectedTxt()"
    [ngStyle]="{
    'width': '98%',
    'height': '65%'}" #canvas ></canvas>

2。 ts文件

@ViewChild('canvas') public canvas: ElementRef;

ionViewDidLoad() {
   console.log('ionViewDidLoad ImageHomePage');
    this.canvasElement = this.canvas.nativeElement;
    this.ctx = this.canvasElement.getContext('2d');
    let image = this.renderer.createElement('img');
    image.src = this.selectedImage;
    this.ctx.drawImage(image,10, 10, this.canvasElement.width, 
    this.canvasElement.height);
}

我还用另一种方式......

I used another way also...

方法2 -

ionViewDidLoad() {
    // this.selectedImage = this.route.snapshot.params['id'];
    console.log('ionViewDidLoad ImageHomePage');
    let canvasID= document.getElementById("canvas") as HTMLCanvasElement; 
    let canvasContext = canvasID.getContext("2d");
    this.canvasElement = this.canvas.nativeElement;
    this.ctx = this.canvasElement.getContext('2d');
    let image = new Image() as HTMLImageElement;
    image.onload = function() {
      canvasContext.drawImage(image, 0, 0, canvasID.width, canvasID.height);
    }
    image.src = this.selectedImage;
}

我可以知道，我做错了什么？我知道这个问题已被问了很多次，我尝试了这些方法，但没有一个对我有用。因此提出问题，可能是其他人将来会面临问题..

May I know, what am I doing wrong? I know this question has been asked so many times, I tried the methods but none of them worked for me.. Hence asking the question, might be others will face issue in future..

推荐答案

最后我解决了问题..

Finally I solved issue..

我添加渲染器2 ..

以下是我的代码..

我在 ionViewDidload（）

let newImg = this.renderer.createElement('img');
newImg.src = this.selectedImage;
newImg.onload  = this.drawImg(newImg);

drawImg(imgContext){
    console.log('drawImg called');
    setTimeout(() => {
      this.ctx.drawImage(imgContext,0,0, this.canvasElement.width, this.canvasElement.height);
    }, 1000);

  }

我打电话给 setTimeout 因为这需要时间。没有 setTimeout 它没有显示任何东西。

I called setTimeout because it was taking time. Without setTimeout it wasn't showing any thing.

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