CODEWITHSUNDEEP
objective-ciosuiwebviewdrawrect
jcrowson
jcrowson

Reputation: 4290

UIWebView to UIImage invalid context 0x0

I'm trying to do a simple task; convert the contents of a UIWebView to a UIImage and save it to the phone's documents directory, however I keep getting a bunch of similar errors every time the following code is run:

  UIGraphicsBeginImageContext(rect.size);
    [self.webView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

Creates the following errors:

Jun 10 20:06:18 <Error>: CGContextSaveGState: invalid context 0x0
Jun 10 20:06:18 <Error>: CGContextSetAlpha: invalid context 0x0
Jun 10 20:06:18 <Error>: CGContextSaveGState: invalid context 0x0
Jun 10 20:06:18 <Error>: CGContextSetFillColorWithColor: invalid context 0x0
Jun 10 20:06:18 <Error>: CGContextAddRect: invalid context 0x0
Jun 10 20:06:18 <Error>: CGContextDrawPath: invalid context 0x0

I did some research and found that this was due to the code above not being in the -(void)drawRect:(CGRect)rect method, however, how do I call this after the UIWebView has been initialised, or do I not call it manually?

This is the code I'm using to create the HTML and load it into the WebView:

-(void)saveHTMLDocument {

    NSMutableString *htmlDocumentToSave = [[NSMutableString alloc] initWithString:@"<html><body>"];
    [htmlDocumentToSave appendString:@"<table border=""1""><tr><th>Snag Number</th><th>Snag Photo</th><th>Snag Description</th><th>Date Taken</th>"];

    for (int i = 0; i < self.fetchedResultsController.fetchedObjects.count; i++) {

    NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation([self.photoArray objectAtIndex:i])];
    NSString *base64String = [imageData base64EncodedString];

    Snag *snag = [self.fetchedResultsController.fetchedObjects objectAtIndex:i];

    NSString *tableString = [NSString stringWithFormat:@"<tr><td>%i</td><td><p><b><img src='data:image/png;base64,%@'></b></p></td><td>%@</td><td>%@</td></tr>", i+1, base64String, snag.snagDescription, snag.dateTaken];
    [htmlDocumentToSave appendString:tableString];

    }

    [htmlDocumentToSave appendString:@"</table></body></html>"];


    //Save the HTMl document that will be attached.
    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsPath = [paths objectAtIndex:0];

    NSString *htmlPath = [documentsPath stringByAppendingPathComponent:@"test"];
    [htmlDocumentToSave writeToFile:htmlPath atomically:NO encoding:NSUTF8StringEncoding error:nil];
    self.htmlData = [NSData dataWithContentsOfFile:htmlPath];

    //Generate the UIWebView and load the HTML into it

    NSString *htmlFile = [[NSBundle mainBundle] pathForResource:@"test" ofType:@"html"];

    NSData *htmlData = [NSData dataWithContentsOfFile:htmlFile];

    self.webView = [[UIWebView alloc] init];
    [self.webView loadData:htmlData MIMEType:@"text/html" textEncodingName:@"UTF-8" baseURL:[NSURL URLWithString:@""]];

    NSString *string = [self.webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('html')[0].innerHTML"];

    NSLog(@"Check if WebView has loaded %@", string);



}

-(void)drawRect:(CGRect)rect {

    UIGraphicsBeginImageContext(rect.size);
    [self.webView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}

Upvotes: 0

Views: 1288

Answers (2)

Kurt Revis
Kurt Revis

Reputation: 27994

What is rect.size? If the width or height are zero, then CG will be unable to create a context, leading to the sorts of errors that you're seeing.

@OmarAbdelhafith is correct about the rest -- you don't have to do this work in -drawRect:, and the rest of your code looks OK. Also, make sure you are running this code after the UIWebView is fully loaded.

Upvotes: 1

Omar Abdelhafith
Omar Abdelhafith

Reputation: 21221

Nope it does not have to be in drawRect, i use this functon

+(UIImage*)captureScreen:(UIView*) viewToCapture
{
    UIGraphicsBeginImageContextWithOptions(viewToCapture.bounds.size, viewToCapture.opaque, 0.0);
    [viewToCapture.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return viewImage;
}

In my app and it correctly takes a screen shot of my WebView

Upvotes: 2

Related Questions