javascript - 无法在 Ionic 3 中链式 promise

Question

我有一个插件，cordova-plugin-datecs-printer ，我可以用它在热敏打印机上打印一些字符串。问题是我无法以这种方式编码打印大量字符串。插件创建者已经通知我，错误在于我处理 promise 的方式，但我已经尝试以不同的方式改变我处理它们的方式，但我没有得到它。我尝试寻找一些示例并了解有关 Promise 的更多信息，但我无法将任何内容应用于此案例。

我的代码:

 printItem(){
        this.print.listBluetoothDevices().then(result => {
          console.log(JSON.stringify(result));
          this.print = result;
        }).catch(err => {

        });

        this.print.connect('00:02:5B:B4:7C:3A').then(result => {
          console.log(JSON.stringify(result));
          this.print = result;
        }).catch(err => {

        });

        var printStr = "";
          printStr += "{reset}{center}Instituto do Meio Ambiente {br}";
          printStr += "------------------------------------------------";
          printStr += "AUTO DE INFRACAO AMBIENTAL 9453-D {br}";
          printStr += "------------------------------------------------";
          printStr += "DADOS DO AUTUADO {br}";

        var printStr2 = "";
          printStr2 += " {br}";
          printStr2 += "{reset}{left}Nome: ";
          printStr2 += "ADD VARIAVEL NOME {br}";
          printStr2 += "CPF: ";
          printStr2 += "ADD VARIAVEL CPF {br}";

        //Promises I want to chain
        this.print.printText(printStr, 'ISO-8859-1');
        this.print.printText(printStr2, 'ISO-8859-1');

        this.print.feedPaper(100).then(result => {
          console.log(JSON.stringify(result));
          this.print = result;
        }).catch(err => {

        });

编辑:我正在使用的提供商(打印):

listBluetoothDevices() {
    return new Promise<any>((resolve, reject) => {
      this.win.DatecsPrinter.listBluetoothDevices((success) => resolve(success), (error) => reject(error));
    });
  }

  connect(deviceAddress: string): Promise<any> {
    return new Promise<any>((resolve, reject) => {
      setTimeout(() => this.win.DatecsPrinter.connect(deviceAddress, (success) => resolve(success), (error) => reject(error)), this.defaultTimeout);
    });
  }

  printText(text: string, charset: string = 'ISO-8859-1'): Promise<any> {
    return new Promise<any>((resolve, reject) => {
      this.win.DatecsPrinter.printText(text, charset, (success) => resolve(success), (error) => reject(error));
    });
  }

Answer 1

您的所有代码都是异步的，因此，所有这些代码将同时执行。

  this.print.connect('00:02:5B:B4:7C:3A').then(result => {
          console.log(JSON.stringify(result));
          this.print = result;
        }).catch(err => {

        });


    var printStr2 = "";
      printStr2 += " {br}";
      printStr2 += "{reset}{left}Nome: ";
      printStr2 += "ADD VARIAVEL NOME {br}";
      printStr2 += "CPF: ";
      printStr2 += "ADD VARIAVEL CPF {br}";

    //Promises I want to chain
    this.print.printText(printStr, 'ISO-8859-1');
    this.print.printText(printStr2, 'ISO-8859-1');

    this.print.feedPaper(100).then(result => {
      console.log(JSON.stringify(result));
      this.print = result;
    }).catch(err => {

    });

为了正确工作，您应该将所有代码放在第一个 Promise 中，如下所示:

this.print.connect('00:02:5B:B4:7C:3A').then(result => {
  console.log(JSON.stringify(result));
  this.print = result;

   // ALL YOUR CODE HERE!!

}).catch(err => {

});