Question

在iOS中，我正在尝试在uiwebview中更新谷歌图表。我使用dispatch_async（dispatch_get_global ...）来解析json信息。在异步调用中，我使用dispatch_async（dispatch_get_main_queue ...）来执行主线程上的UI元素。我仍然在屏幕上发现一些延迟，但没有UI挂起。请帮助我以更好的方式编写下面的代码，这样一旦我从解析的信息中获得价值，我应该能够毫不拖延地生成图表。以下是代码：

dispatch_queue_t syncInAsync=dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);   
dispatch_async(syncInAsync, ^{        
[self parse:url];    
     dispatch_async(dispatch_get_main_queue(), ^{           
 NSString* htmlString = [NSString stringWithFormat:@"<html><head><script type=\"text/javascript\" src=\"https://www.google.com/jsapi\"></script><script type=\"text/javascript\">google.load(\"visualization\", \"1\", {packages:[\"corechart\"]});google.setOnLoadCallback(drawChart);function drawChart() {var data = google.visualization.arrayToDataTable([['Reports', 'Value'],['Total',     %@ ]]);var options = {title: 'Total Reports'};var chart = new google.visualization.PieChart(document.getElementById('piechart'));chart.draw(data, options);}</script></head><body><div id=\"piechart\" style=\" text-align: left width: 400px; height: 200px;\"></div></body></html>",number];           
            [_web1 loadHTMLString:htmlString baseURL:nil];
    });
});

Answer 1

使用sync而不是异步线程更新UI。试试这个 -

 dispatch_queue_t syncInAsync=dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); dispatch_async(syncInAsync, ^{ [self parse:url]; dispatch_sync(dispatch_get_main_queue(), ^{ NSString* htmlString = [NSString stringWithFormat:@"<html><head><script type=\"text/javascript\" src=\"https://www.google.com/jsapi\"></script><script type=\"text/javascript\">google.load(\"visualization\", \"1\", {packages:[\"corechart\"]});google.setOnLoadCallback(drawChart);function drawChart() {var data = google.visualization.arrayToDataTable([['Reports', 'Value'],['Total', %@ ]]);var options = {title: 'Total Reports'};var chart = new google.visualization.PieChart(document.getElementById('piechart'));chart.draw(data, options);}</script></head><body><div id=\"piechart\" style=\" text-align: left width: 400px; height: 200px;\"></div></body></html>",number]; [_web1 loadHTMLString:htmlString baseURL:nil]; }); });

Answer 2

在此块中写下您想要更改的内容

   [[NSOperationQueue mainQueue] addOperationWithBlock:^{
//type here
  }];

Answer 3

你大多以正确的方式做这件事。我想做一些改变：

我想让parse方法执行代码在UI上呈现。所以，传递这样的完成块。在解析过程中显示加载叠加层总是一个好主意：

grep -B1 -A2 "Name: XXX"

这就是你的来电者的样子：

- (void)parse:(NSString *)iURL withCompletionBlock:MyCompletionBlock)iCompletionBlock {
   // Parse JSON here. Show Loading Overlay.

   // Once response is available
    dispatch_async(dispatch_get_main_queue(), ^{
        // Remove Loading Overlay.

        // Execute completion block
        completionBlock();
    });
}

这是更新主线程上的值以更改UI的正确方法吗？

3 个答案: