'尝试打开邮件编辑器时,应用程序尝试在目标'错误/崩溃时呈现nil模态视图控制器

Question

我有一个简单的应用程序,它打开一个模态视图来发送电子邮件.我正在使用Xcode 4.2和iOS 5,并正在使用iOS模拟器进行测试.由于未捕获的异常'NSInvalidArgumentException',应用程序因终止应用程序崩溃 ,原因是:
'应用程序试图在目标上显示一个零模态视图控制器.

执行时:

 [self presentModalViewController:mailComposer animated:YES];

虽然我已经初始化了对象'mailComposer'.

类com_FirstViewController.m:

#import "com_FirstViewController.h"
...
@implementation com_FirstViewController
....
....
-(void)showEmailComposer {

Class mailClass = (NSClassFromString(@"MFMailComposeViewController"));
if (mailClass != nil)
{
    if ([mailClass canSendMail]) {
                    NSLog(@"showEmailComposer: Calling displayComposerSheet");
        [self displayComposerSheet];

    } else {
                    NSLog(@"showEmailComposer: Calling launchMailAppOnDevice");
        [self launchMailAppOnDevice];
    }
}
else {
            NSLog(@"showEmailComposer: Calling launchMailAppOnDevice");
    [self launchMailAppOnDevice];
}
}



#pragma mark -
#pragma mark Compose Mail

-(void) displayComposerSheet {

    mailComposer = [[MFMessageComposeViewController alloc] init];
    mailComposer.messageComposeDelegate = self;

    // Set the mail title
    [mailComposer setTitle:@"Mail Title"];

    // Set the recipients
    NSArray *toRecipients = [NSArray arrayWithObject:@"user@company.com"];

    [mailComposer setRecipients:toRecipients];

    // EMail Body
    NSString *mailBody = @"This is the mail body";
    [mailComposer setBody:mailBody];

    NSLog(@"present the modal view ctlr");
    [self presentModalViewController:mailComposer animated:YES];
}
...
...

有什么指针吗？

Answer 1

我也遇到过类似的问题.我分配了一个实例MFMailComposeViewController并尝试以模态方式呈现它.我也有例外:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Application tried to present a nil modal view controller on target

这是因为在iPhone的设置中禁用了"邮件"选项.当设备中没有设置邮件帐户时也可能是这种情况.因此MFMailCompseViewController实例将以nil模态方式呈现它将导致崩溃.

我用canSendMail的方法MFMailComposeViewController来解决这个问题.

Class mailClass = (NSClassFromString(@"MFMailComposeViewController"));
if (mailClass != nil) {
    MFMailComposeViewController * mailView = [[MFMailComposeViewController alloc] init];
    mailView.mailComposeDelegate = self;

    //Set the subject
    [mailView setSubject:emailSubject];

    //Set the mail body
    [mailView setMessageBody:emailBody isHTML:YES];


    //Display Email Composer
    if([mailClass canSendMail]) {
        [self.navControl presentModalViewController:mailView animated:YES];
    }
}

Answer 2

 mailComposer = [[MFMessageComposeViewController alloc] init];

在我看来,这是问题的根源.模拟器无法发送SMS消息,因此初始化方法可能返回NULL.无论如何,苏似乎想要发送电子邮件,所以我想你需要使用

 mailComposer = [[MFMailComposeViewController alloc] init];