布局裏一個(gè)按鈕，是(shì)調起保存相冊API的(de)，也(yě)就(jiù)保存功能的(de)按鈕。

步驟二：編寫調用保存相冊API的(de)邏輯代碼：

<button hidden='{{!openSettingBtnHidden}}' class="default-btn" hover-class="default-btn-active" bindtap="saveInvoice">保存</button>
<button hidden='{{openSettingBtnHidden}}' class="default-btn" hover-class="default-btn-active" open-type="openSetting" bindopensetting='handleSetting'>去授權</button>

/*下載發票圖片*/
  saveInvoice: function () {
    var self = this,
    timestamp = new Date().getTime(),
    file = wx.getFileSystemManager();
    file.writeFile({
      filePath: `${wx.env.USER_DATA_PATH}/invoice_${timestamp}.jpeg`,
      data: self.data.invoiceImg,
      encoding: 'base64',
      success: res => {
        self.saveToAlbum(timestamp);
      },
      fail: err => {
        showMsg('保存失敗');
      }
    });
  },
  /*保存發票圖片到(dào)用戶相冊，調用小程序API*/
  /*要(yào / yāo)考慮處理用戶拒絕授權之(zhī)後如何重新調起授權請求的(de)問題*/
  saveToAlbum: function (timestamp) {
    var self = this;
    wx.saveImageToPhotosAlbum({
      filePath: `${wx.env.USER_DATA_PATH}/invoice_${timestamp}.jpeg`,
      success: res => {
        showMsg('圖片已保存至相冊');
      },
      fail: err => {
        console.log(err);
        if (err.errMsg === 'saveImageToPhotosAlbum:fail auth deny' || err.errMsg === 'saveImageToPhotosAlbum:fail:auth denied') {
          self.setData({
            openSettingBtnHidden: false
          });
          showMsg('已拒絕授權，請點擊重新授權');
        } else {
          showMsg('保存失敗');
        }
      }
    });
  },

  /*用戶手動重新授權*/
  handleSetting: function(e) {
    var self = this;
    if (!e.detail.authSetting['scope.writePhotosAlbum']) {
      wx.showModal({
        title: '提示',
        content: '若不(bù)打開授權，則無法将圖片保存在(zài)相冊中！',
        showCancel: false
      });
      self.setData({
        openSettingBtnHidden: true
      })
    } else {
      wx.showModal({
        title: '提示',
        content: '您已授權，趕緊将圖片保存在(zài)相冊中吧！',
        showCancel: false
      })
      self.setData({
        openSettingBtnHidden: true
      })
    }
  }