如何以及在哪里使用 JavaScript 通过 C++ 枚举器

枚举器是一个提供遍历容器或集合能力的对象。枚举器可以用来读取集合中的数据，但不能用来修改底层集合，而数组是一种定义了enumerator方法的接口，该方法返回一个IEnumerator接口，从而实现只读访问集合。

Aspose.Cells API提供了一堆枚举器，但本文主要讨论如下三种类型。

单元格枚举器
行枚举器
列枚举器

如何使用枚举器

单元格枚举器

有各种方式可以访问单元格枚举器，并且可以根据应用程序的要求使用任何这些方法。以下是返回单元格枚举器的方法。

上述所有方法都返回允许遍历初始化的单元格集合的枚举器。

在遍历单元格时，集合不应被修改（进行会导致实例化新单元格或删除现有单元格的操作）。否则，枚举器可能无法正确遍历所有单元格（某些元素可能会被重复遍历或被跳过）。

以下代码示例演示了如何实现Cells集合的IEnumerator接口。

<!DOCTYPE html>
<html>
    <head>
        <title>Aspose.Cells Example</title>
    </head>
    <body>
        <h1>Aspose.Cells Example - Read Cell Values</h1>
        <input type="file" id="fileInput" accept=".xls,.xlsx,.csv" />
        <button id="runExample">Run Example</button>
        <a id="downloadLink" style="display: none;">Download Result</a>
        <div id="result"></div>
    </body>

    <script src="aspose.cells.js.min.js"></script>
    <script type="text/javascript">
        const { Workbook, SaveFormat } = AsposeCells;

        AsposeCells.onReady({
            license: "/lic/aspose.cells.enc",
            fontPath: "/fonts/",
            fontList: [
                "arial.ttf",
                "NotoSansSC-Regular.ttf"
            ]
        }).then(() => {
            console.log("Aspose.Cells initialized");
        });

        document.getElementById('runExample').addEventListener('click', async () => {
            const fileInput = document.getElementById('fileInput');
            if (!fileInput.files.length) {
                document.getElementById('result').innerHTML = '<p style="color: red;">Please select an Excel file.</p>';
                return;
            }

            const file = fileInput.files[0];
            const arrayBuffer = await file.arrayBuffer();

            // Instantiating a Workbook object by opening the uploaded Excel file
            const workbook = new Workbook(new Uint8Array(arrayBuffer));

            // Access the first worksheet
            const worksheet = workbook.worksheets.get(0);

            const resultLines = [];

            // Iterate over all cells in the worksheet
            const cellsEnumerator = worksheet.cells.getEnumerator();
            for (const cell of cellsEnumerator) {
                console.log(`${cell.name} ${cell.value}`);
                resultLines.push(`${cell.name} ${cell.value}`);
            }

            // Iterate over the first row's cells
            const firstRowEnumerator = worksheet.cells.rows.get(0).getEnumerator();
            for (const cell of firstRowEnumerator) {
                console.log(`${cell.name} ${cell.value}`);
                resultLines.push(`${cell.name} ${cell.value}`);
            }

            // Iterate over a specific range A1:B10
            const rangeEnumerator = worksheet.cells.createRange("A1:B10").getEnumerator();
            for (const cell of rangeEnumerator) {
                console.log(`${cell.name} ${cell.value}`);
                resultLines.push(`${cell.name} ${cell.value}`);
            }

            document.getElementById('result').innerHTML = `<pre>${resultLines.join('\n')}</pre>`;
        });
    </script>
</html>

行枚举器

在使用RowCollection.enumerator方法时可以访问行枚举器。以下示例代码演示了为RowCollection实现IEnumerator接口的方法。

<!DOCTYPE html>
<html>
    <head>
        <title>Aspose.Cells Example</title>
    </head>
    <body>
        <h1>Aspose.Cells Example - List Row Indexes</h1>
        <input type="file" id="fileInput" accept=".xls,.xlsx,.csv" />
        <button id="runExample">Run Example</button>
        <a id="downloadLink" style="display: none;">Download Result</a>
        <div id="result"></div>
    </body>

    <script src="aspose.cells.js.min.js"></script>
    <script type="text/javascript">
        const { Workbook, SaveFormat } = AsposeCells;

        AsposeCells.onReady({
            license: "/lic/aspose.cells.enc",
            fontPath: "/fonts/",
            fontList: [
                "arial.ttf",
                "NotoSansSC-Regular.ttf"
            ]
        }).then(() => {
            console.log("Aspose.Cells initialized");
        });

        document.getElementById('runExample').addEventListener('click', async () => {
            const fileInput = document.getElementById('fileInput');
            if (!fileInput.files.length) {
                document.getElementById('result').innerHTML = '<p style="color: red;">Please select an Excel file.</p>';
                return;
            }

            const file = fileInput.files[0];
            const arrayBuffer = await file.arrayBuffer();

            // Instantiate Workbook from uploaded file
            const workbook = new Workbook(new Uint8Array(arrayBuffer));

            // Get RowCollection and iterate using index
            const rows = workbook.worksheets.get(0).cells.rows;
            const rowCount = rows.count;

            // Traverse rows in the collection and display indexes
            let output = '<p>Row indexes:</p><ul>';
            for (let i = 0; i < rowCount; i++) {
                const row = rows.get(i);
                output += `<li>${row.index}</li>`;
                console.log(row.index);
            }
            output += '</ul>';
            document.getElementById('result').innerHTML = output;
        });
    </script>
</html>

列枚举器

在使用ColumnCollection.enumerator方法时可以访问列枚举器。以下示例代码演示了为ColumnCollection实现IEnumerator接口的方法。

<!DOCTYPE html>
<html>
    <head>
        <title>Aspose.Cells Example</title>
    </head>
    <body>
        <h1>Read Columns Indexes Example</h1>
        <input type="file" id="fileInput" accept=".xls,.xlsx,.csv" />
        <button id="runExample">Run Example</button>
        <a id="downloadLink" style="display: none;">Download Result</a>
        <div id="result"></div>
    </body>

    <script src="aspose.cells.js.min.js"></script>
    <script type="text/javascript">
        const { Workbook, SaveFormat } = AsposeCells;

        AsposeCells.onReady({
            license: "/lic/aspose.cells.enc",
            fontPath: "/fonts/",
            fontList: [
                "arial.ttf",
                "NotoSansSC-Regular.ttf"
            ]
        }).then(() => {
            console.log("Aspose.Cells initialized");
        });

        document.getElementById('runExample').addEventListener('click', async () => {
            const fileInput = document.getElementById('fileInput');
            if (!fileInput.files.length) {
                document.getElementById('result').innerHTML = '<p style="color: red;">Please select an Excel file.</p>';
                return;
            }

            const file = fileInput.files[0];
            const arrayBuffer = await file.arrayBuffer();

            // Instantiating a Workbook object from uploaded file
            const workbook = new Workbook(new Uint8Array(arrayBuffer));

            // Get columns collection from first worksheet
            const columns = workbook.worksheets.get(0).cells.columns;
            // Traverse columns using index
            const count = columns.count;
            let html = '<p>Columns indexes:</p><ul>';
            for (let i = 0; i < count; i++) {
                const col = columns.get(i);
                html += `<li>${col.index}</li>`;
                console.log(col.index);
            }
            html += '</ul>';
            document.getElementById('result').innerHTML = html;
        });
    </script>
</html>

枚举器的使用场景

为了讨论使用枚举器的优势，让我们以一个实时案例来说明。

情景

应用程序需要遍历给定 Worksheet 中的所有单元格以读取它们的值。实现此目标的方法可能有多种，以下列出几种示例。

使用显示范围

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title>Aspose.Cells Example</title>
    </head>
    <body>
        <h1>Read Max Display Range Example</h1>
        <input type="file" id="fileInput" accept=".xls,.xlsx,.csv" />
        <button id="runExample">Run Example</button>
        <a id="downloadLink" style="display: none;">Download Result</a>
        <div id="result"></div>
    </body>

    <script src="aspose.cells.js.min.js"></script>
    <script type="text/javascript">
        const { Workbook, SaveFormat } = AsposeCells;

        AsposeCells.onReady({
            license: "/lic/aspose.cells.enc",
            fontPath: "/fonts/",
            fontList: [
                "arial.ttf",
                "NotoSansSC-Regular.ttf"
            ]
        }).then(() => {
            console.log("Aspose.Cells initialized");
        });

        document.getElementById('runExample').addEventListener('click', async () => {
            const fileInput = document.getElementById('fileInput');
            const resultDiv = document.getElementById('result');
            resultDiv.innerHTML = '';

            if (!fileInput.files.length) {
                resultDiv.innerHTML = '<p style="color: red;">Please select an Excel file.</p>';
                return;
            }

            const file = fileInput.files[0];
            const arrayBuffer = await file.arrayBuffer();

            // Instantiating a Workbook object by opening the Excel file from the uploaded file
            const workbook = new Workbook(new Uint8Array(arrayBuffer));

            // Get Cells collection of first worksheet
            const cells = workbook.worksheets.get(0).cells;

            // Get the MaxDisplayRange
            const displayRange = cells.maxDisplayRange;

            // Loop over all cells in the MaxDisplayRange
            let outputLines = [];
            for (let row = displayRange.firstRow; row < displayRange.rowCount; row++) {
                for (let col = displayRange.firstColumn; col < displayRange.columnCount; col++) {
                    // Read the Cell value (stringValue property)
                    const cell = displayRange.get(row, col);
                    outputLines.push(cell.stringValue);
                    console.log(cell.stringValue);
                }
            }

            resultDiv.innerHTML = '<pre>' + outputLines.join('\n') + '</pre>';
        });
    </script>
</html>

使用MaxDataRow和MaxDataColumn

<!DOCTYPE html>
<html>
    <head>
        <title>Aspose.Cells Example</title>
        <meta charset="utf-8" />
        <style>
            body { font-family: Arial, sans-serif; margin: 20px; }
            #result { margin-top: 15px; max-height: 400px; overflow: auto; border: 1px solid #ddd; padding: 10px; }
            .cell-value { padding: 2px 0; border-bottom: 1px dashed #eee; }
            .error { color: red; }
        </style>
    </head>
    <body>
        <h1>Read Cells Example</h1>
        <input type="file" id="fileInput" accept=".xlsx,.xls,.csv" />
        <button id="runExample">Run Example</button>
        <a id="downloadLink" style="display: none;">Download Result</a>
        <div id="result"></div>
    </body>

    <script src="aspose.cells.js.min.js"></script>
    <script type="text/javascript">
        const { Workbook } = AsposeCells;

        AsposeCells.onReady({
            license: "/lic/aspose.cells.enc",
            fontPath: "/fonts/",
            fontList: [
                "arial.ttf",
                "NotoSansSC-Regular.ttf"
            ]
        }).then(() => {
            console.log("Aspose.Cells initialized");
        });

        function escapeHtml(text) {
            if (text === null || text === undefined) return '';
            return String(text)
                .replace(/&/g, '&amp;')
                .replace(/</g, '&lt;')
                .replace(/>/g, '&gt;')
                .replace(/"/g, '&quot;')
                .replace(/'/g, '&#039;');
        }

        document.getElementById('runExample').addEventListener('click', async () => {
            const fileInput = document.getElementById('fileInput');
            const resultDiv = document.getElementById('result');
            resultDiv.innerHTML = '';

            if (!fileInput.files.length) {
                resultDiv.innerHTML = '<p class="error">Please select an Excel file.</p>';
                return;
            }

            const file = fileInput.files[0];
            const arrayBuffer = await file.arrayBuffer();

            // Instantiating a Workbook object by opening the Excel file from the uploaded file
            const workbook = new Workbook(new Uint8Array(arrayBuffer));

            // Get Cells collection of first worksheet
            const cells2 = workbook.worksheets.get(0).cells;
            const maxDataRow = cells2.maxDataRow;
            const maxDataColumn = cells2.maxDataColumn;

            const outputLines = [];
            // Loop over all cells
            for (let row = 0; row <= maxDataRow; row++) {
                for (let col = 0; col <= maxDataColumn; col++) {
                    // Read the Cell value
                    const currentCell = cells2.checkCell(row, col);
                    if (currentCell) {
                        const cellText = currentCell.stringValue;
                        outputLines.push('<div class="cell-value">' + escapeHtml(cellText) + '</div>');
                        console.log(cellText);
                    }
                }
            }

            if (outputLines.length === 0) {
                resultDiv.innerHTML = '<p>No cell values found.</p>';
            } else {
                resultDiv.innerHTML = outputLines.join('');
            }
        });
    </script>
</html>

正如您所注意到的，上述两种方法都使用了几乎相似的逻辑，即在集合中循环遍历所有单元格以读取单元格的值。对于许多原因，这可能会有问题，如下所讨论的。

maxRow、maxDataRow、maxColumn、maxDataColumn 和 maxDisplayRange 等API需要额外时间来收集相应的统计信息。如果数据矩阵（行×列）很大，使用这些API可能会影响性能。
在大多数情况下，给定范围中并非所有单元格都被实例化。在这种情况下，检查矩阵中的每个单元格比仅检查初始化的单元格效率低。
在循环中访问单元格作为Cells row, column将导致范围内的所有单元格对象被实例化，这最终可能导致OutOfMemoryException。

结论

基于上述事实，以下是应该使用枚举器的可能情况。

需要只读访问单元格集合，即只需检查单元格。
需要遍历大量的单元格。
只需遍历已初始化的单元格/行/列。

查找或搜索数据数据筛选