Question

我有一个单例类，我已经用java的方式实现了它：

companion object {

    @Volatile private lateinit var instance: TrapBridge

    fun bridge(): TrapBridge {
        if (!this::instance.isInitialized) {
            synchronized(this) {
                if (!this::instance.isInitialized) {
                    instance = TrapBridge()
                }
            }
        }
        return instance
    }

}

现在的问题是我无法使用isInitialized属性，因为它引发了NoSuchFieldError异常：

java.lang.NoSuchFieldError: No field instance of type Lcom/sample/trap/model/TrapBridge; in class Lcom/sample/trap/model/TrapBridge$Companion; or its superclasses (declaration of 'com.sample.trap.model.TrapBridge$Companion' appears in /data/app/com.sample.trapsample-L9D8b2vxEQfiSg9Qep_eNw==/base.apk)

我认为这是因为instance是类变量，而不是实例变量，因此我无法使用this关键字来引用它：/

我也无法检查它是否为null，因为它会抛出UninitializedPropertyAccessException：

lateinit property instance has not been initialized

Answer 1

很遗憾，这是一个已知问题，已在官方Kotlin问题跟踪器上here进行了跟踪。

Answer 2

我遇到了同样的问题，并找到了另一种方法：

// Import the library
var Excel = require('exceljs'),
    moment = require('moment'),
    // Define Excel filename
    ExcelFile = 'so.xlsx',
    // Read from the file
    workbook = new Excel.Workbook();

workbook.xlsx.readFile(ExcelFile)
    .then(function()
    {
        // Use workbook
        var dataSheet = workbook.getWorksheet('Sheet 1'),
            masterSheet = workbook.getWorksheet('Sheet 2');

        dataSheet.eachRow({ includeEmpty: false }, function(dataRow, dataRowNumber)
        {
            var dataRowCells =
                {
                    dataCell1: dataRow.getCell('A'),
                    dataCell2: dataRow.getCell('B'),
                    dataCell3: dataRow.getCell('C')
                },
                isdataRowOK = false,
                oneOfBestMasterRowNumber,
                cellNames = ['A','B','C'];

            masterSheet.eachRow({ includeEmpty: false }, function(masterRow, masterRowNumber)
            {
                if(!isdataRowOK)
                {
                    var numberOfGoodCellsInRow = 0;

                    for(var i = 1; i < 4; i++)
                        if(dataRowCells['dataCell' + i].value === masterRow.getCell(cellNames[i-1]).value)
                            numberOfGoodCellsInRow++;

                    if(numberOfGoodCellsInRow == 2)
                        oneOfBestMasterRowNumber = masterRowNumber;

                    if(numberOfGoodCellsInRow == 3)
                        isdataRowOK = true
                }
            });


            if(!isdataRowOK)
            {
                var masterRowForCheck = masterSheet.getRow(oneOfBestMasterRowNumber);

                for(var i = 1; i < 4; i++)
                {
                    var dataCell = dataRowCells['dataCell' + i];
                    if(dataCell.value !== masterRowForCheck.getCell(cellNames[i-1]).value)
                    {
                        // Mark this failed cell as color red
                        dataCell.style = Object.create(dataCell.style); // Shallow-clone the style, break references
                        dataCell.fill = {type: 'pattern', pattern:'solid', fgColor:{argb:'FA8072'}}; // Set background
                    }
                }

            }
        });

        return workbook.xlsx.writeFile('new.xlsx');
    });

lateinit的isInitialized属性在伴侣对象中不起作用

2 个答案: