在phonegap中将base64字符串转换为pdf

Question

In my app I have received a base64 string that represents a PDF. I want the user to be able to save the base64 as a pdf to his phone. I have been looking in to the cordova-file-transfer plugin but that requires a (server)path where the file can be downloaded from, instead of converting a base64 string.

Has anybody succeeded in downloading a pdf in phonegap using a base64 string?

Answer 1

After some more searching and trying I found something that worked.

Converting base64 to pdf blob

//Helper function that converts base64 to blob
function b64toBlob(b64Data, contentType, sliceSize) {
    var input = b64Data.replace(/\s/g, ''),
        byteCharacters = atob(input),
        byteArrays = [],
        offset, slice, byteNumbers, i, byteArray, blob;

    contentType = contentType || '';
    sliceSize = sliceSize || 512;

    for (offset = 0; offset < byteCharacters.length; offset += sliceSize) {
        slice = byteCharacters.slice(offset, offset + sliceSize);

        byteNumbers = new Array(slice.length);
        for (i = 0; i < slice.length; i++) {
            byteNumbers[i] = slice.charCodeAt(i);
        }

        byteArray = new Uint8Array(byteNumbers);

        byteArrays.push(byteArray);
    }

    //Convert to blob. 
    try {
        blob = new Blob(byteArrays, { type: contentType });
    }
    catch (e) {
        // TypeError old chrome, FF and Android browser
        window.BlobBuilder = window.BlobBuilder ||
                             window.WebKitBlobBuilder ||
                             window.MozBlobBuilder ||
                             window.MSBlobBuilder;
        if (e.name == 'TypeError' && window.BlobBuilder) {
            var bb = new BlobBuilder();
            for (offset = 0; offset < byteArrays.length; offset += 1) {
                bb.append(byteArrays[offset].buffer);
            }                    
            blob = bb.getBlob(contentType);
        }
        else if (e.name == "InvalidStateError") {
            blob = new Blob(byteArrays, {
                type: contentType
            });
        }
        else {
            return null;
        }
    }

    return blob;
};

And then the downloading itself we need the cordova-file plugin:

var fileToSave= b64toBlob(fileData, 'application/pdf'); 
writeFile();

function writeFile() {
    console.log("request file system");
    window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, onFileSystemRetrieved, onFileSystemFail);
}

function onFileSystemRetrieved(fileSystem) {
    console.log("file system retrieved");
    fileSystem.root.getFile(fileName, { create: true }, onFileEntryRetrieved, onFileSystemFail);
}

function onFileEntryRetrieved(fileEntry) {
    console.log("file entry retrieved");
    fileEntry.createWriter(gotFileWriter, onFileSystemFail);
}

function gotFileWriter(writer) {
    console.log("write to file");

    writer.onwrite = function (evt) {
        alert('done');
    }
    writer.write(fileToSave);

    window.open(fileName, '_blank');
}
function onFileSystemFail(error) {
    console.log(error.code);
    alert(error.code)
}