防止程序输入时候产生错误后，锁定屏幕崩溃

- (void)applicationDidEnterBackground:(UIApplication *)application{
// Use this method to release shared resources, save user data,
// invalidate timers, and store enough application state information to
// restore your application to its current state in case it is terminated later.
// If your application supports background execution,
// this method is called instead of applicationWillTerminate: when the user quits.
if (([[[UIDevice currentDevice] systemVersion] floatValue] >= 6.0))
{
// Acquired additional time
UIDevice *device = [UIDevice currentDevice];
BOOL backgroundSupported = NO;
if ([device respondsToSelector:@selector(isMultitaskingSupported)])
{
backgroundSupported = device.multitaskingSupported;
}
if (backgroundSupported)
{
backgroundTask = [application beginBackgroundTaskWithExpirationHandler:^{
[application endBackgroundTask:backgroundTask];
backgroundTask = UIBackgroundTaskInvalid;
}];
}
}
return;
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

其中的backgroundTask 是成员变量。

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }