my.offUserCaptureScreen

// Remove all screenshot listeners
my.offUserCaptureScreen();

Page({
  onLoad() {
    my.onUserCaptureScreen(this.handleScreenshot);
  },

  handleScreenshot() {
    console.log('Screenshot taken');
  },

  onUnload() {
    my.offUserCaptureScreen(this.handleScreenshot);
  }
});

Page({
  data: {
    screenshotHandlerActive: false
  },

  enableScreenshotHandler() {
    my.onUserCaptureScreen(this.onScreenshot);
    this.setData({ screenshotHandlerActive: true });
  },

  disableScreenshotHandler() {
    my.offUserCaptureScreen(this.onScreenshot);
    this.setData({ screenshotHandlerActive: false });
  },

  onScreenshot() {
    my.showSharePanel();
  }
});