//文字生成圖片

-(UIImage *)imageFromText:(NSString *)contentStr withFont: (UIFont *)font
{
    
    //確定文字的size
    CGFloat imageWidth = [UIScreen mainScreen].bounds.size.width - 20;
    CGSize contentSize = [contentStr boundingRectWithSize:CGSizeMake(imageWidth, 0) options:NSStringDrawingUsesFontLeading attributes:@{NSFontAttributeName : font} context:nil].size;
    
    UIGraphicsBeginImageContextWithOptions(contentSize,NO,0.0);
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSetCharacterSpacing(ctx, 10);
    CGContextSetTextDrawingMode (ctx, kCGTextFill);
    CGContextSetRGBFillColor (ctx, 0.1, 0.2, 0.3, 1); // 6
    CGContextSetRGBStrokeColor (ctx, 0, 0, 0, 1);
    
    CGRect rect = CGRectMake(0, 0, contentSize.width, contentSize.height );
    [contentStr drawInRect:rect withAttributes:@{NSFontAttributeName : font}];
    
    // transfer image
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    
    return image;
    
}