递归调用使用承诺（块写）的JS函数

Question

我想写一个函数，递归调用自己将块写入磁盘块。虽然递归工作和块进展，但我搞乱了如何处理返回的承诺，因为函数实例化自己的承诺，并且在写入完成时需要返回。首先使用isAppend = false从调用函数调用writeFile2。

function writeFile2(path, file, blob, isAppend) 
    { 
     var csize = 4 * 1024 * 1024; // 4MB 
     var d = $q.defer(); 
     console.log ("Inside write file 2 with blob size="+blob.size); 

     // nothing more to write, so all good? 
     if (!blob.size) 
     { 
      // comes here at the end, but since d is instantiated on each 
      // call, I guess the promise chain messes up and the invoking 
      // function never gets to .then 
      console.log ("writefile2 all done"); 
      d.resolve(true); 
      return d.promise; 
     } 
     // first time, create file, second time onwards call append 

     if (!isAppend) 
     { 
      $cordovaFile.writeFile(path, file, blob.slice(0,csize), true) 
      .then (function (succ) { 
        return writeFile2(path,file,blob.slice(csize),true); 
      }, 
      function (err) { 
       d.reject(err); 
       return d.promise; 

      }); 
     } 
     else 
     { 
     $cordovaFile.writeExistingFile(path, file, blob.slice(0,csize)) 
     .then (function (succ) { 
       return writeFile2(path,file,blob.slice(csize),true); 
     }, 
     function (err) { 
      d.reject(err); 
      return d.promise; 

     }); 
     } 

     return d.promise; 
    } 

Answer 1

当您调用另一个方法时，返回返回的承诺，而不是您自己的。当没有工作要做时，请回到你自己的承诺。

function writeFile2(path, file, blob, isAppend) { 
    var csize = 4 * 1024 * 1024; // 4MB 
    console.log ("Inside write file 2 with blob size="+blob.size); 

    // nothing more to write, so all good? 
    if (!blob.size) 
    { 
     // nothing to do, just resolve to true 
     console.log ("writefile2 all done"); 
     return $q.resolve(true); 
    } 
    // first time, create file, second time onwards call append 

    if (!isAppend) 
    { 
     // return the delegated promise, even if it fails 
     return $cordovaFile.writeFile(path, file, blob.slice(0,csize), true) 
      .then (function (succ) { 
       return writeFile2(path,file,blob.slice(csize),true); 
      }); 
    } 
    else 
    { 
     // return the delegated promise, even if it fails 
     return $cordovaFile.writeExistingFile(path, file, blob.slice(0,csize)) 
      .then (function (succ) { 
       return writeFile2(path,file,blob.slice(csize),true); 
      }); 
    } 
}