“无效的句柄"创建CGBitmapContext [英] "Invalid Handle" Create CGBitmapContext

问题描述

我在CGBitmapcontext上遇到了问题. 使用消息无效的句柄"创建CGBitmapContext时出现错误.

I've got a problem with the CGBitmapcontext. I get en error while creating the CGBitmapContext with the message "invalid Handle".

这是我的代码:

var previewContext = new CGBitmapContext(null, (int)ExportedImage.Size.Width, (int)ExportedImage.Size.Height, 8, (int)ExportedImage.Size.Height * 4,                                                    CGColorSpace.CreateDeviceRGB(), CGImageAlphaInfo.PremultipliedFirst);

谢谢；

推荐答案

这是因为您要将null传递给第一个参数. CGBitmapContext用于直接绘制到内存缓冲区中.构造函数所有重载中的第一个参数是(Apple docs):

That is because you are passing null to the first parameter. The CGBitmapContext is for drawing directly into a memory buffer. The first parameter in all the overloads of the constructor is (Apple docs):

数据 指向内存中要绘制图形的目标的指针.该内存块的大小至少应为 (bytesPerRow * height)个字节.

data A pointer to the destination in memory where the drawing is to be rendered. The size of this memory block should be at least (bytesPerRow*height) bytes.

在MonoTouch中，为方便起见，我们得到两个接受byte []的重载.因此，您应该像这样使用它:

In MonoTouch, we get two overloads that accept a byte[] for convenience. So you should use it like this:

int bytesPerRow = (int)ExportedImage.Size.Width * 4; // note that bytes per row should 
    //be based on width, not height.
byte[] ctxBuffer = new byte[bytesPerRow * (int)ExportedImage.Size.Height];
var previewContext = 
    new CGBitmapContext(ctxBuffer, (int)ExportedImage.Size.Width, 
    (int)ExportedImage.Size.Height, 8, bytesPerRow, colorSpace, bitmapFlags);

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