带图标的 Xamarin.Forms 列表应用程序（仅限 Android）

Question

我有一个 Xamarin Forms 项目，我尝试使用带有图标的已安装应用程序列表。

现在我有标签，但我没有得到图像。

我使用依赖服务来获取应用程序列表。：

public IEnumerable<IAppListServiceApplication> GetApplications()
        {
            var apps = Android.App.Application.Context.PackageManager.GetInstalledApplications(PackageInfoFlags.MatchAll);
            foreach (var app in apps)
            {
                var label = app.LoadLabel(Android.App.Application.Context.PackageManager);
                if (!label.ToLower().StartsWith("com."))
                    yield return new AppListServiceApplication
                    {
                        Label = label,
                        PackageName = app.PackageName,
                        AppIcon = GetAppIcon(app)
                    };
            }
        }

但我无法在 Xamarin Forms 项目中将 Android Drawable 对象转换为 ImageSource。这是我现在尝试的：

public ImageSource GetAppIcon(ApplicationInfo app)
        {
            try
            {
                var drawable = app.LoadIcon(Android.App.Application.Context.PackageManager);

                //return ImageSource.FromStream(() => new MemoryStream(bytes));
                Bitmap icon = drawableToBitmap(drawable);

                return ImageSource.FromStream(() => MemoryStreamFromBitmap(icon));
            }
            catch (Exception ex)
            {
                var message = ex.ToString();
                return null;
            }


        }
        MemoryStream MemoryStreamFromBitmap(Bitmap bmp)
        {
            MemoryStream stream = new MemoryStream();
            bmp.Compress(Bitmap.CompressFormat.Png, 0, stream);
            return stream;
        }
        Bitmap drawableToBitmap(Drawable drawable)
        {
            Bitmap bitmap = null;

            if (drawable is BitmapDrawable) {
                BitmapDrawable bitmapDrawable = (BitmapDrawable)drawable;
                if (bitmapDrawable.Bitmap != null)
                {
                    return bitmapDrawable.Bitmap;
                }
            }
            if (drawable is AdaptiveIconDrawable)
            {
                AdaptiveIconDrawable adaptiveIconDrawable = (AdaptiveIconDrawable)drawable;
                if (!(adaptiveIconDrawable.IntrinsicWidth <= 0 || adaptiveIconDrawable.IntrinsicHeight <= 0))
                {
                    bitmap = Bitmap.CreateBitmap(drawable.IntrinsicWidth, drawable.IntrinsicHeight, Bitmap.Config.Argb8888);
                    Canvas c = new Canvas(bitmap);
                    drawable.SetBounds(0, 0, c.Width, c.Height);
                    drawable.Draw(c);
                    return bitmap;

                }
            }

            if (drawable.IntrinsicWidth <= 0 || drawable.IntrinsicHeight <= 0)
            {
                bitmap = Bitmap.CreateBitmap(1, 1, Bitmap.Config.Argb8888); // Single color bitmap will be created of 1x1 pixel
            }
            else
            {
                bitmap = Bitmap.CreateBitmap(drawable.IntrinsicWidth, drawable.IntrinsicHeight, Bitmap.Config.Argb8888);
            }

            Canvas canvas = new Canvas(bitmap);
            drawable.SetBounds(0, 0, canvas.Width, canvas.Height);
            drawable.Draw(canvas);
            return bitmap;
        }

如您所见，我是 xamarin 和 Android 的新手 ^^ 。我没有在 Google 上找到如何从 Android 传递 Drawable 以在 Xamarin Forms 中显示它。

如果你能指出我正确的方向，以了解如何做到这一点。

坦克

编辑：添加输出错误

我在输出窗口中收到此错误：

ImageLoaderSourceHandler: Image data was invalid: Xamarin.Forms.StreamImageSource
11-05 04:31:19.287 D/skia    (10270): --- SkAndroidCodec::NewFromStream returned null

**编辑：** 添加项目

这是 gitHub 中的问题：https : //github.com/werddomain/Xamarin-Android-Laucher/tree/master/Forms/AndroidCarLaucher

Answer 1

创建一个ImageSource将图标作为其原始加载的新图标Drawable与转换为位图、字节数组等相比，速度更快、内存效率更高……这也适用于 ListView 中的回收单元等……

ImageSource 实现（存在于 .NetStd/Forms 库中）：

[TypeConverter(typeof(PackageNameSourceConverter))]
public sealed class PackageNameSource : ImageSource
{
    public static readonly BindableProperty PackageNameProperty = BindableProperty.Create(nameof(PackageName), typeof(string), typeof(PackageNameSource), default(string));

    public static ImageSource FromPackageName(string packageName)
    {
        return new PackageNameSource { PackageName = packageName };
    }

    public string PackageName
    {
        get { return (string)GetValue(PackageNameProperty); }
        set { SetValue(PackageNameProperty, value); }
    }

    public override Task<bool> Cancel()
    {
        return Task.FromResult(false);
    }

    public override string ToString()
    {
        return $"PackageName: {PackageName}";
    }

    public static implicit operator PackageNameSource(string packageName)
    {
        return (PackageNameSource)FromPackageName(packageName);
    }

    public static implicit operator string(PackageNameSource packageNameSource)
    {
        return packageNameSource != null ? packageNameSource.PackageName : null;
    }

    protected override void OnPropertyChanged(string propertyName = null)
    {
        if (propertyName == PackageNameProperty.PropertyName)
            OnSourceChanged();
        base.OnPropertyChanged(propertyName);
    }
}

TypeConverter 实现（存在于 .NetStd/Forms 库中）：

[TypeConversion(typeof(PackageNameSource))]
public sealed class PackageNameSourceConverter : TypeConverter
{
    public override object ConvertFromInvariantString(string value)
    {
        if (value != null)
            return PackageNameSource.FromPackageName(value);

        throw new InvalidOperationException(string.Format("Cannot convert \"{0}\" into {1}", value, typeof(PackageNameSource)));
    }
}

IImageSourceHandler、IImageViewHandler 实现（存在于 Xamarin.Android 项目中）：

public class PackageNameSourceHandler : IImageSourceHandler, IImageViewHandler
{
    public async Task<Bitmap> LoadImageAsync(ImageSource imagesource, Context context, CancellationToken cancelationToken = default(CancellationToken))
    {
        var packageName = ((PackageNameSource)imagesource).PackageName;
        using (var pm = Application.Context.PackageManager)
        using (var info = pm.GetApplicationInfo(packageName, PackageInfoFlags.MetaData))
        using (var drawable = info.LoadIcon(pm))
        {
            Bitmap bitmap = null;
            await Task.Run(() =>
            {
                bitmap = Bitmap.CreateBitmap(drawable.IntrinsicWidth, drawable.IntrinsicHeight, Bitmap.Config.Argb8888);
                using (var canvas = new Canvas(bitmap))
                {
                    drawable.SetBounds(0, 0, canvas.Width, canvas.Height);
                    drawable.Draw(canvas);
                }
            });
            return bitmap;
        }
    }

    public Task LoadImageAsync(ImageSource imagesource, ImageView imageView, CancellationToken cancellationToken = default(CancellationToken))
    {
        var packageName = ((PackageNameSource)imagesource).PackageName;
        using (var pm = Application.Context.PackageManager)
        {
            var info = pm.GetApplicationInfo(packageName, PackageInfoFlags.MetaData);
            imageView.SetImageDrawable(info.LoadIcon(pm));
        }
        return Task.FromResult(true);
    }
}

注意：在程序集级别注册：

[assembly: ExportImageSourceHandler(typeof(PackageNameSource), typeof(PackageNameSourceHandler))]

现在，在您的依赖项服务中返回至少包含 PackageName 的 Android 应用程序列表，类似于 IList<Package>

public class Package
{
    public string Name { get; set; }
    public string PackageName { get; set; }
}

Xml 示例：

现在您可以使用以下命令将其绑定IList<Package>到ListView自定义单元格PackageNameSource：

<Image WidthRequest="60" HeightRequest="60">
    <Image.Source>
        <local:PackageNameSource PackageName="{Binding PackageName}" />
    </Image.Source>
</Image>