错误TypeError: this.signaturePad.set不是函数

Question

我正在用ngx-signaturepad开发一个angular6项目。我遵循了文档https://www.npmjs.com/package/ngx-signaturepad，但是我得到了错误'ERROR TypeError: this.signaturePad.set is not a function‘，并且没有在我的项目中显示记号板。

import { SignaturePadModule } from 'ngx-signaturepad';

...

@NgModule({
  declarations: [ ],
  imports: [ SignaturePadModule ],
  providers: [ ],
  bootstrap: [ AppComponent ]
})

// then import for use in a component

import { Component, ViewChild } from '@angular/core';
import { SignaturePad } from 'ngx-signaturepad/signature-pad';

@Component({
  template: '<signature-pad [options]="signaturePadOptions" (onBeginEvent)="drawStart()" (onEndEvent)="drawComplete()"></signature-pad>'
})

export class SignaturePadPage{

  @ViewChild(SignaturePad) signaturePad: SignaturePad;

  private signaturePadOptions: Object = { // passed through to szimek/signature_pad constructor
    'minWidth': 5,
    'canvasWidth': 500,
    'canvasHeight': 300
  };

  constructor() {
    // no-op
  }

  ngAfterViewInit() {
    // this.signaturePad is now available
    this.signaturePad.set('minWidth', 5); // set szimek/signature_pad options at runtime
    this.signaturePad.clear(); // invoke functions from szimek/signature_pad API
  }

  drawComplete() {
    // will be notified of szimek/signature_pad's onEnd event
    console.log(this.signaturePad.toDataURL());
  }

  drawStart() {
    // will be notified of szimek/signature_pad's onBegin event
    console.log('begin drawing');
  }
}

​

​

Answer 1

我会尝试两件事。第一个方法是为模板中的元素分配一个ID，比如#signaturePad，然后在ViewChild声明中引用它。像这样的东西

@Component({
  template: '<signature-pad #signaturePanel [options]="signaturePadOptions" (onBeginEvent)="drawStart()" (onEndEvent)="drawComplete()"></signature-pad>'
})

export class SignaturePadPage{

  @ViewChild("signaturePanel") signaturePad: SignaturePad;
...

看起来问题在于你的变量没有正确初始化。这可能是由于错误的引用造成的，或者可能是组件显示后的初始化时间。您可以尝试在ngAfterViewInit中添加setTimeout，以检查是否发生了这种情况。如下所示：

ngAfterViewInit() {
setTimeout(()=>{
    this.signaturePad.set('minWidth', 5); // set szimek/signature_pad options at runtime
    this.signaturePad.clear(); // invoke functions from szimek/signature_pad API
},1000) //After 1 Second
}

Answer 2

我怀疑当您尝试设置宽度时，可能没有完全初始化。利用onBeginEvent事件，而不是调用AfterViewInit方法。下面提供了一个示例。

import { SignaturePadModule } from 'ngx-signaturepad';

...

@NgModule({
  declarations: [ ],
  imports: [ SignaturePadModule ],
  providers: [ ],
  bootstrap: [ AppComponent ]
})

// then import for use in a component

import { Component, ViewChild } from '@angular/core';
import { SignaturePad } from 'ngx-signaturepad/signature-pad';

@Component({
  template: '<signature-pad [options]="signaturePadOptions" (onBeginEvent)="drawStart()" (onEndEvent)="drawComplete()"></signature-pad>'
})

export class SignaturePadPage{

  @ViewChild(SignaturePad) signaturePad: SignaturePad;

  private signaturePadOptions: Object = { // passed through to szimek/signature_pad constructor
    'minWidth': 5,
    'canvasWidth': 500,
    'canvasHeight': 300
  };

  constructor() {
    // no-op
  }

  drawComplete() {
    // will be notified of szimek/signature_pad's onEnd event
    console.log(this.signaturePad.toDataURL());
  }

  drawStart() {
    // will be notified of szimek/signature_pad's onBegin event
    console.log('begin drawing');
    this.configureSignaturePad();
  }

  private configureSignaturePad() {
    // this.signaturePad is now available
    this.signaturePad.set('minWidth', 5); // set szimek/signature_pad options at runtime
    this.signaturePad.clear(); // invoke functions from szimek/signature_pad API
  }
}```