Nutch 1.4与Solr 3.4 - 无法抓取网址，“无法抓取网址”(Nutch 1.4 with Solr 3.4 - can't crawl URL, “no URLs to fetch”)

 替代方法： 
 
 您可以创建一系列表示进度更新的图像，然后在进程的每个步骤中使用setImage：forState：方法替换UIButton currentImage属性。 这不需要在现有视图中绘制，这种方法对我来说很有效，可以显示图像（按钮或其他）的简单“动画”。 
 
 这种方法对你有用吗？ 如果没有，为什么不呢？ 
 
 巴特 

This was really bugging me so after dealing with a series of silly, but necessary issues regarding the project I want this functionality for, I played around with it. The end result is that I can now arbitrarily draw an arc representing the progress of a particular background task to a button.
 
The goal was to draw something like the little indicator in the lower right hand corner of the XCode windows while a project is being cleaned or compiled.
 
I created a function that will draw and fill an arc and return it as a UIImage.
 
The worker thread calls method (PerformSelectorOnMainThread) with the current values and a button identifier. In the called method, I call the arc image function with the percentage filled and such.
 
example call:
 
oImg = [self ArcImageCreate:100.0f fWidth:100.0f 
    fPercentFilled: 0.45f fAngleStart: 0.0f xFillColor:[UIColor blueColor]];
 
Then set the background image of the button:
 
[oBtn setBackgroundImage: oImg forState: UIControlStateNormal];
 
Here is the function:
 It is not finished, but it works well enough to illustrate how I am doing this.
 


/**
ArcImageCreate
@ingroup    UngroupedFunctions
@brief  Create a filled or unfilled solid arc and return it as a UIImage.

        Allows for dynamic / arbitrary update of an object that allows a UIImage to be drawn on it. \
    This can be used for some sort of pie chart or progress indicator by Image Flipping.

@param  fHeight     The height of the created UIImage.
@param  fWidth      The width of the created UIImage.
@param  fPercentFilled  A percentage of the circle to be filled by the arc. 0.0 to 1.0.
@param  AngleStart  The angle where the arc should start. 0 to 360. Clock Reference.
@param  xFillColor  The color of the filled area.

@return Pointer to a UIImage.

@todo [] Validate object creation at each step.

@todo [] Convert PercentFilled (0.0 to 1.0) to appropriate radian(?) (-3.15 to +3.15)

@todo [] Background Image Support. Allow for the arc to be drawn on top of an image \
    and the whole thing returned.

@todo [] Background Image Reduction. Background images will have to be resized to fit the specfied size. \
    Do not want to return a 65KB object because the background is 60K or whatever.

@todo [] UIColor RGBA Components. Determine a decent method of extracting RGVA values \
    from a UIColor*. Check out arstechnica.com/apple/guides/2009/02/iphone-development-accessing-uicolor-components.ars \
    for an idea.

*/
- (UIImage*) ArcImageCreate: (float)fHeight fWidth:(float)fWidth fPercentFilled:(float)fPercentFilled fAngleStart:(float)fAngleStart xFillColor:(UIColor*)xFillColor
{
    UIImage* fnRez = nil;
    float fArcBegin = 0.0f;
    float fArcEnd = 0.0f;
    float fArcPercent = 0.0f;
    UIColor* xArcColor = nil;
    float fArcImageWidth = 0.0f;
    float fArcImageHeight = 0.0f;
    CGRect xArcImageRect;

    CGContextRef xContext = nil;
    CGColorSpaceRef xColorSpace;
    void* xBitmapData;
    int iBMPByteCount;
    int iBMPBytesPerRow;
    float fPI = 3.14159;
    float fRadius = 25.0f;

// @todo Force default of 100x100 px if out of bounds. \
//  Check max image dimensions for iPhone. \
//  If negative, flip values *if* values are 'reasonable'. \
//  Determine minimum useable pixel dimensions. 10x10 px is too small. Or is it?
    fArcImageWidth = fHeight;
    fArcImageHeight = fWidth;

    // Get the passed target percentage and clip it between 0.0 and 1.0
    fArcPercent = (fPercentFilled  1.0f) ? 1.0f : fPercentFilled;
    fArcPercent = (fArcPercent > 1.0f) ? 1.0f : fArcPercent;

    // Get the passed start angle and clip it between 0.0 to 360.0
    fArcBegin = (fAngleStart  359.0f) ? 0.0f : fAngleStart;
    fArcBegin = (fArcBegin > 359.0f) ? 0.0f : fArcBegin;

    fArcBegin = (fArcBegin * fPI) / 180.0f;
    fArcEnd = ((360.0f * fArcPercent) * fPI) / 180.0f;

    // 
    if (xFillColor == nil) {
        // random color
    } else {
        xArcColor = xFillColor;
    }

    // Calculate memory required for image.
    iBMPBytesPerRow = (fArcImageWidth * 4);
    iBMPByteCount = (iBMPBytesPerRow * fArcImageHeight);
    xBitmapData = malloc(iBMPByteCount);

    // Create a color space. Behavior changes at OSXv10.4. Do not rely on it for consistency across devices.
    xColorSpace = CGColorSpaceCreateDeviceRGB();

    // Set the system to draw. Behavior changes at OSXv10.3.
    //  Both of these work. Not sure which is better.
//  xContext = CGBitmapContextCreate(xBitmapData, fArcImageWidth, fArcImageHeight, 8, iBMPBytesPerRow, xColorSpace, kCGImageAlphaPremultipliedFirst);
    xContext = CGBitmapContextCreate(NULL, fArcImageWidth, fArcImageHeight, 8, iBMPBytesPerRow, xColorSpace, kCGImageAlphaPremultipliedFirst);

    // Let the system know the colorspace reference is no longer required.
    CGColorSpaceRelease(xColorSpace);

    // Set the created context as the current context.
//  UIGraphicsPushContext(xContext);

    // Define the image's box.
    xArcImageRect = CGRectMake(0.0f, 0.0f, fArcImageWidth, fArcImageHeight);

    // Clear the image's box.
//  CGContextClearRect(xContext, xRect);

    // Draw the ArcImage's background image.
//  CGContextDrawImage(xContext, xArcImageRect, [oBackgroundImage CGImage]);

    // Set Us Up The Transparent Drawing Area.
    CGContextBeginTransparencyLayer(xContext, nil);

    // Set the fill and stroke colors
// @todo [] Determine why SetFilColor does not. Use alternative method.
//  CGContextSetFillColor(xContext, CGColorGetComponents([xArcColor CGColor]));
//  CGContextSetFillColorWithColor(xContext, CGColorGetComponents([xArcColor CGColor]));
// Test Colors
    CGContextSetRGBFillColor(xContext, 0.3f, 0.4f, 0.5f, 1.0f);
    CGContextSetRGBStrokeColor(xContext, 0.5f, 0.6f, 0.7f, 1.0f);
    CGContextSetLineWidth(xContext, 1.0f);

// Something like this to reverse drawing?
//  CGContextTranslateCTM(xContext, TranslateXValue, TranslateYValue);
//  CGContextScaleCTM(xContext, -1.0f, 1.0f); or CGContextScaleCTM(xContext, 1.0f, -1.0f);

    // Test Vals
//  fArcBegin = 45.0f * fPI / 180.0f;   // 0.785397
//  fArcEnd = 90.0f * fPI / 180.0f; // 1.570795

    // Move to the start point and draw the arc.
    CGContextMoveToPoint(xContext, fArcImageWidth/2.0f, fArcImageHeight/2.0f);
    CGContextAddArc(xContext, fArcImageWidth/2.0f, fArcImageHeight/2.0f, fRadius, fArcBegin, fArcEnd, 0);


    // Ask the OS to close the arc (current point to starting point). 
    CGContextClosePath(xContext);

    // Fill 'er up. Implicit path closure.
    CGContextFillPath(xContext);
//  CGContextEOFillPath(context);

    // Close Transparency drawing area.
    CGContextEndTransparencyLayer(xContext);

    // Create an ImageReference and create a UIImage from it.
    CGImageRef xCGImageTemp = CGBitmapContextCreateImage(xContext);
    CGContextRelease(xContext);
    fnRez = [UIImage imageWithCGImage: xCGImageTemp];
    CGImageRelease(xCGImageTemp);

//  UIGraphicsPopContext;

    return fnRez;
}