Bitmap.FromFile(路径)和新位图(路径)之间的区别

Question

我想知道这两者之间的区别:

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

一种选择比另一种更好吗？是否Bitmap.FromFile(path)会向位图图像填充任何其他数据,或者它只是一个委托new Bitmap(path)？

Answer 1

可通过基类“ Image”（它是抽象类）到“ Bitmap”类使用“ FromFile”方法，并且该方法返回Image对象。其中“ Bitmap”是继承“ Image”类的子类，而Bitmap构造函数允许您直接初始化Bitmap对象。

在您的情况下，您要尝试的是调用FromFile方法并获取一个Image对象，然后将其类型转换为Bitmap。当您让Bitmap构造函数执行此操作时，为什么要执行此操作。Bitmap.FromFile（path）是否将任何其他数据填充到位图图像中：否

Answer 2

两种方法都通过参数获取图像的句柄path。Image.FromFile将返回超类Image，而前者只会返回，Bitmap因此您可以避免强制转换。

在内部，他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;
}

和：

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);
}