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我正在尝试做一个简单的任务；将 UIWebView 的内容转换为 UIImage 并将其保存到手机的文档目录中，但是每次运行以下代码时，我都会收到一堆类似的错误：

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

创建以下错误：

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

我做了一些研究，发现这是由于上面的代码不在 -(void)drawRect:(CGRect)rect 方法中，但是，在 UIWebView 初始化后如何调用它，或者我不调用它手动？

这是我用来创建 HTML 并将其加载到 WebView 中的代码：

-(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();
}
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2 回答 2

2

不，它不必在drawRect中，我使用这个功能

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

在我的应用程序中，它正确地截取了我的 WebView 的屏幕截图

于 2012-06-10T19:50:56.983 回答
1

是什么rect.size？如果宽度或高度为零，则 CG 将无法创建上下文，从而导致您看到的各种错误。

@OmarAbdelhafith 关于其余部分是正确的——您不必在 中进行这项工作-drawRect:，并且您的其余代码看起来还可以。此外，请确保在UIWebView完全加载后运行此代码。

于 2012-06-10T19:54:26.433 回答