Question

我试图在打印预览选项中显示字符串值。如果我没有在任何文本字段中输入任何文本，并且在单击打印按钮时应用程序崩溃。错误是[__NSCFString appendString：]：nil参数'。这是我的代码

-(NSMutableString*)pageStringToPrint {

    NSMutableString * cnoteString = [[NSMutableString alloc]init];

    [cnoteString setString:@"Class: "];
    [cnoteString appendString:self.cnote.classname];
    [cnoteString appendString:@"\nTeacher: "];
    [cnoteString appendString:self.cnote.teacher];
    [cnoteString appendString:@"\nSource: "];
    [cnoteString appendString:self.cnote.source];
    [cnoteString appendString:@"\nTopic: "];
    [cnoteString appendString:self.cnote.topic];

    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"MM-dd-yyyy"];
    NSString *dateString = [dateFormat stringFromDate:self.cnote.date];
    [cnoteString appendString:@"\nDate: "];
    [cnoteString appendString: dateString];  

    cnoteString = [NSMutableString stringWithFormat:@"<div id=\"mainContainer\"><div id=\"header\">%@</div>",[cnoteString kv_encodeHTMLCharacterEntities]];

这就是我创建Self.cnoe.classname

的方式

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    [self saveCNote ];
    self.classNameTextField.text = self.cnote.classname;
    self.topicTextField.text = self.cnote.topic;
    self.sourceTextField.text = self.cnote.source;
    self.teacherTextField.text = self.cnote.teacher;


    self.essentialQuestionTextView.placeholder = @"Essential Question";
    self.essentialQuestionTextView.layer.cornerRadius = 7.0f;
    self.essentialQuestionTextView .layer.borderColor = [[UIColor grayColor] CGColor];
    self.essentialQuestionTextView.layer.borderWidth= 1.0f;
    self.essentialQuestionTextView.delegate = self;
    self.essentialQuestionTextView.text = self.cnote.essentialQuestion;

    // set the date
    self.dateTextField.delegate = self;
    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"MM-dd-yyyy"];
    self.dateTextField.text = [dateFormat    stringFromDate:self.cnote.date];
  }

保存Cnote：

- (void)saveCNote {

    self.cnote.classname = self.classNameTextField.text;
    self.cnote.topic = self.topicTextField.text;
    self.cnote.source = self.sourceTextField.text;
    self.cnote.teacher = self.teacherTextField.text;


    [self.cnote save];
}

Answer 1

您应该像nil这样添加判断：

-(NSMutableString*)pageStringToPrint {

    NSMutableString * cnoteString = [[NSMutableString alloc]init];

    [cnoteString setString:@"Class: "];
    [cnoteString appendString:self.note.classname ?: @""];
    [cnoteString appendString:@"\nTeacher: "];
    [cnoteString appendString:self.note.teacher ?: @""];
    [cnoteString appendString:@"\nSource: "];
    [cnoteString appendString:self.note.source ?: @""];
    [cnoteString appendString:@"\nTopic: "];
    [cnoteString appendString:self.note.topic ?: @""];

    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"MM-dd-yyyy"];
    NSString *dateString = [dateFormat stringFromDate:self.note.date] ?: @"";
    [cnoteString appendString:@"\nDate: "];
    [cnoteString appendString: dateString];  

    cnoteString = [NSMutableString stringWithFormat:@"<div id=\"mainContainer\"><div id=\"header\">%@</div>",[cnoteString kv_encodeHTMLCharacterEntities]];

[__NSCFString appendString：]：nil参数'错误

1 个答案: