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从 .NET MAUI Blazor 切换到 WebView 控件进行文档扫描

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2024-07-29 18:37:22918浏览

在.NET MAUI开发中，BlazorWebView和WebView都用于显示网页内容，但它们的用途不同，针对不同的场景而设计。 BlazorWebView 专门设计用于在 .NET MAUI 应用程序中托管 Blazor 组件，允许您重用 Blazor 组件并在 Web 和本机应用程序之间共享代码。 WebView 是用于显示 Web 内容的通用控件，包括网页、HTML 字符串和本地 HTML 文件。在本文中，我们将探讨如何使用 WebView 控件将 .NET MAUI Blazor 文档扫描仪应用程序转换为 .NET MAUI 应用程序，以 JavaScript 和 HTML 实现文档扫描逻辑，并实现 C# 和 JavaScript 之间的互操作以扫描文档和保存图像。

先决条件

  1. 安装 Dynamsoft 服务：此服务对于与 Windows 和 macOS 上的 TWAIN、SANE、ICA、ESCL 和 WIA 扫描仪进行通信是必需的。
    • Windows：Dynamsoft-Service-Setup.msi
    • macOS：Dynamsoft-Service-Setup.pkg
  2. 申请免费试用许可证：获取 Dynamic Web TWAIN 的 30 天免费试用许可证以开始使用。

第 1 步：使用 WebView 控件创建新的 .NET MAUI 项目

  1. 在 Visual Studio 或 Visual Studio Code 中，创建一个新的 .NET MAUI 项目。

  2. 打开 MainPage.xaml 文件并将现有代码替换为以下 XAML 以添加 WebView 控件：

    <?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MauiWebView.MainPage">

    <ScrollView>
        <StackLayout
            VerticalOptions="FillAndExpand"
HorizontalOptions="FillAndExpand">
            <WebView
    x:Name="WebView"
    VerticalOptions="FillAndExpand"
    HorizontalOptions="FillAndExpand" Navigating="OnWebViewNavigated"/>

        </StackLayout>
    </ScrollView>

</ContentPage>

  3. 打开 MainPage.xaml.cs 文件并添加以下代码来设置 WebView 的来源并处理 Navigating 事件：

    namespace MauiWebView
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
            LoadHtmlFile();
        }

        private void LoadHtmlFile()
        {
            WebView.Source = "index.html";

        }

        private async void OnWebViewNavigated(object sender, WebNavigatingEventArgs e)
        {
            if (e.Url.StartsWith("invoke://callcsharpfunction"))
            {
                // TODO: Implement interop between C# and JavaScript
            }
        }
    }

}

    说明：

    • LoadHtmlFile方法设置WebView控件的Source属性来加载index.html文件。
    • 当 WebView 导航到新 URL 时，会触发 OnWebViewNaviged 方法。它检查 URL 是否以 invoke://callcsharpfunction 开头，如果是，则允许 C# 和 JavaScript 互操作。

步骤 2：将静态 HTML、JavaScript 和 CSS 文件加载到 WebView 控件中

在 .NET MAUI 项目中，您可以将位于 Resources/Raw 文件夹中的静态 HTML、JavaScript 和 CSS 文件加载到 WebView 中。确保 MauiAsset 构建操作包含在 .csproj 文件中：

d0fd252dd0536d593a865b1b7d180310
    a6b6999ef84f0df9dca4c12a06340421
6e5ad26193226e804779ce3cd902f2c9

Switching from .NET MAUI Blazor to WebView Control for Document Scanning

我们在index.html 文件中创建与之前的 Blazor 文档扫描仪应用程序类似的 UI 布局。

8b05045a5be5764f313ed5b9168a17e6
49099650ebdc5f3125501fa170048923

93f0f5c25f18dab9d176bd4f6de5d30e
    1fc2df4564f5324148703df3b6ed50c1
    4f2fb0231f24e8aef524fc9bf9b9874f

    b2386ffb911b14667cb8f0f91ea547a7Dynamsoft RESTful API Example6e916e0f7d1e588d4f442bf645aedb2f
    ea507197563fe9808580cd58ff5dae83
9c3bca370b5104690d9ef395f2c5f8d1

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    38b885ab7897934b555c67b94cd711e2
        0a6bb94971119ee328f517322c66980c16b28748ea4df4d9c2150843fecfba68
    16b28748ea4df4d9c2150843fecfba68

    c1a436a314ed609750bd7c7d319db4daDocument Scanner2e9b454fa8428549ca2e64dfac4625cd
    39bbc163833ae4e036fa5108a4263823
        dc6dce4a544fdca2df29d5ac0ea9906b
            2e1cf0710519d5598b1f0f14c36ba674
                Get a License key from e854f899d6c08fe1c619c9c20acd0fd7here5db79b134e9f6b82c0b36e0489ee08ed.
            8c1ecd4bb896b2264e0711597d40766c
            1a7f7aaa14e20835a1a1338a7058be2a
            df250b2156c434f3390392d09b1c9563
        16b28748ea4df4d9c2150843fecfba68

    16b28748ea4df4d9c2150843fecfba68

    4883ec0eb33c31828b7c767c806e14c7
        b91e30dda1382ac7285aae3f45407cef
            684271ed9684bde649abda8831d4d355Acquire Image39528cedfa926ea0c01e69ef5b2ea9b0
            b6f796d82ff1b4e710c079542e89e182Get Devices65281c5ac262bf6d81768915a4a77ac0

            dc6dce4a544fdca2df29d5ac0ea9906b
                6870baf322929e763a5a4dd5b95638a2Source: 8c1ecd4bb896b2264e0711597d40766c
                4e4da74db0fbe784cd1a8c486f2d663a18bb6ffaf0152bbe49cd8a3620346341
            16b28748ea4df4d9c2150843fecfba68

            dc6dce4a544fdca2df29d5ac0ea9906b
                5d63dc371f715490ca7f6d2e4600ec66Pixel Type: 8c1ecd4bb896b2264e0711597d40766c
                5eeb331c51742deae3114e4956cc1be1
                    5a07473c87748fb1bf73f23d45547ab8B &amp; W4afa15d3069109ac30911f04c56f3338
                    5a07473c87748fb1bf73f23d45547ab8Gray4afa15d3069109ac30911f04c56f3338
                    5a07473c87748fb1bf73f23d45547ab8Color4afa15d3069109ac30911f04c56f3338
                18bb6ffaf0152bbe49cd8a3620346341
            16b28748ea4df4d9c2150843fecfba68

            dc6dce4a544fdca2df29d5ac0ea9906b
                045b2ead8e25645fdd0c39f585f1e5bfResolution: 8c1ecd4bb896b2264e0711597d40766c
                c0e226d2d22b2a84209a20e9fa5db602
                    5a07473c87748fb1bf73f23d45547ab81004afa15d3069109ac30911f04c56f3338
                    5a07473c87748fb1bf73f23d45547ab81504afa15d3069109ac30911f04c56f3338
                    5a07473c87748fb1bf73f23d45547ab82004afa15d3069109ac30911f04c56f3338
                    5a07473c87748fb1bf73f23d45547ab83004afa15d3069109ac30911f04c56f3338
                18bb6ffaf0152bbe49cd8a3620346341
            16b28748ea4df4d9c2150843fecfba68


            dc6dce4a544fdca2df29d5ac0ea9906b
                1ee9335f254f79d03a6febbcf5d3d46b
                2c55b6d296473c35276f4ed5dfe2cf7dShow UI8c1ecd4bb896b2264e0711597d40766c
            16b28748ea4df4d9c2150843fecfba68
            dc6dce4a544fdca2df29d5ac0ea9906b
                5ebf17639bf6105e4664ab2e1fb1f6eb
                07c2649bd6a78c967126bb66652d154bADF8c1ecd4bb896b2264e0711597d40766c
            16b28748ea4df4d9c2150843fecfba68
            dc6dce4a544fdca2df29d5ac0ea9906b
                44173729fcd0e865b8455eb3701b40b7
                9fb9d3e7b5ec672c901c914afe880bd9Duplex8c1ecd4bb896b2264e0711597d40766c
            16b28748ea4df4d9c2150843fecfba68

            ebf9f28c318eafce2dd4c8e1bb2c253cScan Now65281c5ac262bf6d81768915a4a77ac0
            6d9fd183d333544e9d5fe06824808c81Save65281c5ac262bf6d81768915a4a77ac0

            684271ed9684bde649abda8831d4d355Image Tools39528cedfa926ea0c01e69ef5b2ea9b0
            2326325328cfb1510e6119c7566a1325
                679019de3d0cfbcca4676917ab8cd4f0
                    803a9dc7ffbcccf77de190935b40089a
                65281c5ac262bf6d81768915a4a77ac0
                becd6db3ab50097bcb2036771f348f01
                    b411ae39fbc39f0429a39ad945dcd511
                65281c5ac262bf6d81768915a4a77ac0
                c56962c63fec7fa8fb3820e921cf15bf
                    b02f8f3397f265cf44c9fcab016cc9c7
                65281c5ac262bf6d81768915a4a77ac0
            16b28748ea4df4d9c2150843fecfba68
        16b28748ea4df4d9c2150843fecfba68

        b3be3238529c3d77b69b7fd150fd938b
            46c5d3aad1e47bee946e6355bc5143b4
                ec6b4fd79f2415f29f0b734dcd571fb5
            16b28748ea4df4d9c2150843fecfba68

            39bbc163833ae4e036fa5108a4263823
                b7c1222a61bcb1861cf5c6bfedb3b7cd
                    a1e9e9b21d1fae6be88debb6fb09c6cc 
                    16b28748ea4df4d9c2150843fecfba68
                16b28748ea4df4d9c2150843fecfba68
            16b28748ea4df4d9c2150843fecfba68
        16b28748ea4df4d9c2150843fecfba68
    16b28748ea4df4d9c2150843fecfba68

    e803653d6fd93b3996ebf69dd59af1622cacc6d41bbb37262a98f745aa00fbf0
36cc49f0c466276486e50c850b7e4956

73a6ac4ed44ffec12cee46588e518a5e

第 3 步：用 JavaScript 实现文档扫描

环境准备好了，下一步就是用JavaScript实现相关功能。

获取设备

枚举可用的扫描仪。

const ScannerType = {
    // TWAIN scanner type, represented by the value 0x10
    TWAINSCANNER: 0x10,

    // WIA scanner type, represented by the value 0x20
    WIASCANNER: 0x20,

    // 64-bit TWAIN scanner type, represented by the value 0x40
    TWAINX64SCANNER: 0x40,

    // ICA scanner type, represented by the value 0x80
    ICASCANNER: 0x80,

    // SANE scanner type, represented by the value 0x100
    SANESCANNER: 0x100,

    // eSCL scanner type, represented by the value 0x200
    ESCLSCANNER: 0x200,

    // WiFi Direct scanner type, represented by the value 0x400
    WIFIDIRECTSCANNER: 0x400,

    // WIA-TWAIN scanner type, represented by the value 0x800
    WIATWAINSCANNER: 0x800
};

let queryDevicesButton = document.getElementById("query-devices-button");
queryDevicesButton.onclick = async () => {
    let scannerType = ScannerType.TWAINSCANNER | ScannerType.TWAINX64SCANNER;
    let devices = await getDevices(host, scannerType);
    let select = document.getElementById("sources");
    select.innerHTML = '';
    for (let i = 0; i e5a00d500dd47a53c4e20100e3fbebf9 {
    let select = document.getElementById("sources");
    let device = select.value;

    if (device == null || device.length == 0) {
        alert('Please select a scanner.');
        return;
    }

    let inputText = document.getElementById("inputText").value;
    let license = inputText.trim();

    if (license == null || license.length == 0) {
        alert('Please input a valid license key.');
    }

    let parameters = {
        license: license,
        device: JSON.parse(device)['device'],
    };

    let showUICheck = document.getElementById("showUICheckId");

    let pixelTypeSelect = document.getElementById("pixelTypeSelectId");

    let resolutionSelect = document.getElementById("resolutionSelectId");

    let adfCheck = document.getElementById("adfCheckId");

    let duplexCheck = document.getElementById("duplexCheckId");

    parameters.config = {
        IfShowUI: showUICheck.checked,
        PixelType: pixelTypeSelect.selectedIndex,
        Resolution: parseInt(resolutionSelect.value),
        IfFeederEnabled: adfCheck.checked,
        IfDuplexEnabled: duplexCheck.checked,
    };


    let jobId = await scanDocument(host, parameters);
    let images = await getImages(host, jobId);

    for (let i = 0; i 30f38ec796a9a4f3b797e10c6aa42e38 {
                if (e != null && e.target != null) {
                    let target = e.target;
                    img.src = target.src;
                    selectedThumbnail = target;
                }
            });
        }

        selectedThumbnail = newImage;
    }

}

async function scanDocument(host, parameters, timeout = 30) {
    let url = host + '/DWTAPI/ScanJobs?timeout=' + timeout;

    try {
        let response = await fetch(url, {
            method: 'POST',
            headers: {
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(parameters)
        });

        if (response.ok) {
            let jobId = await response.text();
            return jobId;
        }
        else {
            return '';
        }
    } catch (error) {
        alert(error);
        return '';
    }
}

async function getImages(host, jobId) {
    let images = [];
    let url = host + '/DWTAPI/ScanJobs/' + jobId + '/NextDocument';

    while (true) {
        try {

            let response = await fetch(url);

            if (response.status == 200) {
                const arrayBuffer = await response.arrayBuffer();
                const blob = new Blob([arrayBuffer], { type: response.type });
                const imageUrl = URL.createObjectURL(blob);

                images.push(imageUrl);
            }
            else {
                break;
            }

        } catch (error) {
            console.error('No more images.');
            break;
        }
    }

    return images;
}

说明

  • scanDocument 函数向 RESTful API 端点 /DWTAPI/ScanJobs 发送 POST 请求以启动扫描作业。参数包括许可证密钥、设备名称和扫描设置。
  • getImages 函数向 RESTful API 端点 /DWTAPI/ScanJobs/{jobId}/NextDocument 发送 GET 请求以获取扫描图像。图像存储在 blob 对象中并显示在图像显示区域中。

旋转图像

将扫描图像旋转-90 或 90 度。

let rotateLeftButton = document.getElementById("rotate-left-button");
rotateLeftButton.onclick = () => {
    let img = document.getElementById('document-image');
    img.src = rotateImage('document-image', -90);
    selectedThumbnail.src = img.src;
}

let rotateRightButton = document.getElementById("rotate-right-button");
rotateRightButton.onclick = () => {
    let img = document.getElementById('document-image');
    img.src = rotateImage('document-image', 90);
    selectedThumbnail.src = img.src;
}

    function rotateImage (imageId, angle) {
    const image = document.getElementById(imageId);
    const canvas = document.createElement('canvas');
    const context = canvas.getContext('2d');
    const imageWidth = image.naturalWidth;
    const imageHeight = image.naturalHeight;

    // Calculate the new rotation
    let rotation = 0;
    rotation = (rotation + angle) % 360;

    // Adjust canvas size for rotation
    if (rotation === 90 || rotation === -270 || rotation === 270) {
        canvas.width = imageHeight;
        canvas.height = imageWidth;
    } else if (rotation === 180 || rotation === -180) {
        canvas.width = imageWidth;
        canvas.height = imageHeight;
    } else if (rotation === 270 || rotation === -90) {
        canvas.width = imageHeight;
        canvas.height = imageWidth;
    } else {
        canvas.width = imageWidth;
        canvas.height = imageHeight;
    }

    // Clear the canvas
    context.clearRect(0, 0, canvas.width, canvas.height);

    // Draw the rotated image on the canvas
    context.save();
    if (rotation === 90 || rotation === -270) {
        context.translate(canvas.width, 0);
        context.rotate(90 * Math.PI / 180);
    } else if (rotation === 180 || rotation === -180) {
        context.translate(canvas.width, canvas.height);
        context.rotate(180 * Math.PI / 180);
    } else if (rotation === 270 || rotation === -90) {
        context.translate(0, canvas.height);
        context.rotate(270 * Math.PI / 180);
    }
    context.drawImage(image, 0, 0);
    context.restore();

    return canvas.toDataURL();
}

删除图像

删除所有扫描图像，包括主图像和缩略图，并重置数据数组。

let deleteButton = document.getElementById("delete-button");
deleteButton.onclick = async () => {
    let img = document.getElementById('document-image');
    img.src = 'images/default.png';
    data = [];
    let thumbnails = document.getElementById("thumb-box");
    thumbnails.innerHTML = '';
}

步骤 4：C# 和 JavaScript 之间的互操作以保存图像

出于安全考虑，直接在 JavaScript 中保存图像受到限制。因此，我们需要在 C# 和 JavaScript 之间进行互操作来完成此任务。

  1. 创建一个 JavaScript 函数，将扫描的图像转换为 Base64 字符串。

    function getBase64Image() {
    var img = document.getElementById('document-image');
    var canvas = document.createElement('canvas');
    canvas.width = img.naturalWidth;
    canvas.height = img.naturalHeight;
    var ctx = canvas.getContext('2d');
    ctx.drawImage(img, 0, 0);

    var dataURL = canvas.toDataURL('image/png'); 
    var base64 = dataURL.split(',')[1]; 
    return base64;
}

  2. 点击保存按钮时，设置window.location.href以触发WebView控件的OnWebViewNaviged事件处理程序。

    let saveButton = document.getElementById("save-button");
saveButton.onclick = async () => {
    window.location.href = 'invoke://CallCSharpFunction';    
}

  3. 在 OnWebViewNaviged 事件处理程序中，调用 EvaluateJavaScriptAsync 从 JavaScript 检索 Base64 图像数据并将其保存到文件中。

    private async void OnWebViewNavigated(object sender, WebNavigatingEventArgs e)
{
    if (e.Url.StartsWith("invoke://callcsharpfunction"))
    {
        var base64String = await WebView.EvaluateJavaScriptAsync("getBase64Image()");
        CallCSharpFunction(base64String);
    }
}

private void CallCSharpFunction(string base64String)
{
    if (!string.IsNullOrEmpty(base64String))
    {

        try
        {
            byte[] imageBytes = Convert.FromBase64String(base64String);

            var filePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), GenerateFilename());
            File.WriteAllBytes(filePath, imageBytes);
            DisplayAlert("Success", "Image saved to: " + filePath, "OK");

        }
        catch (Exception ex)
        {
            DisplayAlert("Error", ex.Message, "OK");
        }
    }
    else
    {
        DisplayAlert("Failure", "No image data found", "OK");
    }
}

private string GenerateFilename()
{
    DateTime now = DateTime.Now;
    string timestamp = now.ToString("yyyyMMdd_HHmmss");
    return $"image_{timestamp}.png";
}

Note: Do not pass the base64 string directly to the C# function via window.location.href, as the string may be too long and cause an error. Instead, return the base64 string when calling EvaluateJavaScriptAsync from the C# function.

Step 5: Run the .NET MAUI Document Scanner Application

Press F5 in Visual Studio or Visual Studio Code to run the .NET document scanner application on Windows or macOS.

Switching from .NET MAUI Blazor to WebView Control for Document Scanning

Source Code

https://github.com/yushulx/dotnet-twain-wia-sane-scanner/tree/main/examples/MauiWebView

以上是从 .NET MAUI Blazor 切换到 WebView 控件进行文档扫描的详细内容。更多信息请关注PHP中文网其他相关文章！

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