从代码更改角度材料进度条颜色

问题描述

我需要动态更改角度材质进度条的颜色.我意识到事情没那么简单，那么最好的方法是什么?

I need to change the color of angular material progress bar dynamically.I realized that it is not that simple, so what is the best way to to it?

要求:

1. 我将从外部 API 接收颜色十六进制代码.所以我不能创建一组预定义的主题
2. 背景颜色将为白色.所以，我只需要一种颜色，而不是整个调色板(较浅、较深)的颜色.

相关链接:(1)

推荐答案

我们可以创建一个属性指令，它接受颜色值并为我们覆盖 的默认样式.

We can create an attribute directive which accepts the color value and override default styles of <mat-progress-bar> for us.

这是一个工作演示:https://stackblitz.com/edit/材料进度条颜色指令

这里是一个简单的解释:

here is a brief explanation:

如果我们在开发者工具中检查 .我们会发现进度条的颜色是在 ::after 伪元素中定义的，就像这样.

If we inspect <mat-progress-bar> in developer tools. we will find that color of the progress-bar is defined in the ::after pseudo element like this.

.mat-progress-bar-fill::after {
    background-color: #3f51b5;
}

正如我们已经知道的那样，不可能使用 DOM querySelector() 方法直接操作一个伪元素.但是我们可以添加新的样式，这些样式也可以包含伪元素的规则.查看此线程以获取更多详细信息.https://stackoverflow.com/a/21709814/1160236

And as we already know that it is not possible to directly manipulate a pseudo element using DOM querySelector() method. But we can add new styles which can have rules for pseudo elements too. checkout this thread for more details. https://stackoverflow.com/a/21709814/1160236

所以，我们可以制定一个指令来为我们添加新的样式.

So, we can make a directive which can take care of adding new styles for us.

import { Directive, Input, OnChanges, SimpleChanges, ElementRef } from '@angular/core';

@Directive({
  selector: '[appProgressBarColor]'
})
export class ProgressBarColor implements OnChanges{
  static counter = 0;

  @Input() appProgressBarColor;
  styleEl:HTMLStyleElement = document.createElement('style');

  //generate unique attribule which we will use to minimise the scope of our dynamic style
  uniqueAttr = `app-progress-bar-color-${ProgressBarColor.counter++}`;

  constructor(private el: ElementRef) {
    const nativeEl: HTMLElement = this.el.nativeElement;
    nativeEl.setAttribute(this.uniqueAttr,'');
    nativeEl.appendChild(this.styleEl);
  }

  ngOnChanges(changes: SimpleChanges): void{
    this.updateColor();
  }

  updateColor(): void{
    // update dynamic style with the uniqueAttr
    this.styleEl.innerText = `
      [${this.uniqueAttr}] .mat-progress-bar-fill::after {
        background-color: ${this.appProgressBarColor};
      }
    `;
  }

}

如您所见，我们在这里所做的只是创建一个新的 HtmlStyleElement 并将其添加到宿主元素中.

as you can see that all that we are doing here is just making a new HtmlStyleElement and adding it just inside the host element.

在 updateColor() 方法中，我们正在更新我们附加的样式标签的 innerText.请注意，我们在这里使用了一个带有唯一属性的属性选择器，以将样式的范围仅用于宿主.因为我们只想为应用了指令的进度条覆盖样式.

And inside updateColor() method we are updating the innerText of the style tag we have appended. notice that we are using an attribute selector here with a unique attribute to minimize the scope of the style to the host only. because we want to override the style only for that progress-bar on which we have applied our directive.

您可以像这样在模板中使用此指令.

you can use this directive in your template like this.

<mat-progress-bar [appProgressBarColor]="'orange'"
                  mode="determinate"
                  value="40"></mat-progress-bar>

我希望这会有所帮助.

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