Bitmap. fromfile (path)和new Bitmap(path)的区别

本文关键字：Bitmap path 区别 fromfile new | 更新日期: 2023-09-27 18:09:49

我想知道这两者的区别:

Bitmap bitmap1 = new Bitmap("C:''test.bmp");
Bitmap bitmap2 = (Bitmap) Bitmap.FromFile("C:''test.bmp");

一个选项比另一个更好吗?Bitmap.FromFile(path)填充任何额外的数据到位图图像或它只是一个委托给new Bitmap(path) ?

Bitmap. fromfile (path)和new Bitmap(path)的区别

FromFile方法来自抽象基类Image，它返回一个Image对象。然而Bitmap类继承了Image类，并且Bitmap构造函数允许你直接初始化Bitmap对象。

在第二行代码中，您要做的是调用FromFile()并获得Image对象，然后将其类型转换为Bitmap。当位图constructor可以为您完成时，手动执行此操作并不是一个很好的理由。

两个方法都通过path参数获得图像的句柄。Image.FromFile将返回超类Image，而前者将简单地返回Bitmap，因此您可以避免强制转换。

在内部，它们几乎做同样的事情:

public static Image FromFile(String filename,
                                     bool useEmbeddedColorManagement)
{
    if (!File.Exists(filename)) 
    {
        IntSecurity.DemandReadFileIO(filename);
        throw new FileNotFoundException(filename);
    }
    filename = Path.GetFullPath(filename);
    IntPtr image = IntPtr.Zero;
    int status;
    if (useEmbeddedColorManagement) 
    {
        status = SafeNativeMethods.Gdip.GdipLoadImageFromFileICM(filename, out image);
    }
    else 
    {
        status = SafeNativeMethods.Gdip.GdipLoadImageFromFile(filename, out image);
    }
    if (status != SafeNativeMethods.Gdip.Ok)
        throw SafeNativeMethods.Gdip.StatusException(status);
    status = SafeNativeMethods.Gdip.GdipImageForceValidation(new HandleRef(null, image));
    if (status != SafeNativeMethods.Gdip.Ok)
    {
        SafeNativeMethods.Gdip.GdipDisposeImage(new HandleRef(null, image));
        throw SafeNativeMethods.Gdip.StatusException(status);
    }
    Image img = CreateImageObject(image);
    EnsureSave(img, filename, null);
    return img;
}

: 

public Bitmap(String filename) 
{
    IntSecurity.DemandReadFileIO(filename);
    filename = Path.GetFullPath(filename);
    IntPtr bitmap = IntPtr.Zero;
    int status = SafeNativeMethods.Gdip.GdipCreateBitmapFromFile(filename, out bitmap);
    if (status != SafeNativeMethods.Gdip.Ok)
        throw SafeNativeMethods.Gdip.StatusException(status);
    status = SafeNativeMethods.Gdip.GdipImageForceValidation(new HandleRef(null, bitmap));
    if (status != SafeNativeMethods.Gdip.Ok) 
    {
        SafeNativeMethods.Gdip.GdipDisposeImage(new HandleRef(null, bitmap));
        throw SafeNativeMethods.Gdip.StatusException(status);
    }
    SetNativeImage(bitmap);
    EnsureSave(this, filename, null);
}

很难说-内部两个方法非常接近，除了Image.FromFile()将检查文件是否存在，如果不存在则抛出FileNotFoundException。

主要区别在于Bitmap.ctor()内部调用GdipCreateBitmapFromFile，而Image.FromFile()内部调用GdipLoadImageFromFile;

这些gdip方法导致了两篇MSDN文章(bitmap . tor() &Image.FromFile())，它们彼此非常接近，但是支持的文件格式似乎有所不同:

Bitmap: BMP, GIF, JPEG, PNG, TIFF, Exif, WMF, and EMF
Image:  BMP, GIF, JPEG, PNG, TIFF, and EMF.

无论如何，如果你知道你将有位图，我更喜欢new Bitmap("C:''test.bmp")只是为了摆脱需要转换图像之后。

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