objective-c 无法在 UILabel 上设置文本字段
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Unable to set text field on UILabel
提问by lucasweb
I have created UITableCellViewclass called NoteCell. The header defines the following:
我创建了一个UITableCellView名为NoteCell. 标题定义了以下内容：
#import <UIKit/UIKit.h>
#import "Note.h"
@interface NoteCell : UITableViewCell {
Note *note;
UILabel *noteTextLabel;
}
@property (nonatomic, retain) UILabel *noteTextLabel;
- (Note *)note;
- (void)setNote:(Note *)newNote;
@end
In the implementation I have the following code for the setNote:method:
在实现中，我有以下setNote:方法代码：
- (void)setNote:(Note *)newNote {
note = newNote;
NSLog(@"Text Value of Note = %@", newNote.noteText);
self.noteTextLabel.text = newNote.noteText;
NSLog(@"Text Value of Note Text Label = %@", self.noteTextLabel.text);
[self setNeedsDisplay];
}
This fails to set the text field of the UILabeland the output of the log messages is:
这无法设置 的文本字段，UILabel并且日志消息的输出是：
2008-11-03 18:09:05.611 VisualNotes[5959:20b] Text Value of Note = Test Note 1
2008-11-03 18:09:05.619 VisualNotes[5959:20b] Text Value of Note Text Label = (null)
I have also tried to set the text field of UILabelusing the following syntax:
我还尝试UILabel使用以下语法设置文本字段：
[self.noteTextLabel setText:newNote.noteText];
This does not seem to make a difference.
这似乎没有什么区别。
Any help would be much appreciated.
任何帮助将非常感激。
回答by Ben Gottlieb
Have you set up your noteTextLabel anywhere? What this looks like to me is that you're messaging a nil object. When you cell is created, noteTextLabel is nil. If you never set it up, you're basically doing the following:
你有没有在任何地方设置过你的 noteTextLabel？在我看来，您正在向一个 nil 对象发送消息。创建单元格时，noteTextLabel 为零。如果您从未设置过它，那么您基本上是在执行以下操作：
[nil setText: newNote.noteText];
And when you later try to access it, you're doing this:
当您稍后尝试访问它时，您正在这样做：
[nil text];
Which will return nil.
这将返回零。
In your -initWithFrame:reuseIdentifier:method, you need to explicitly create your noteTextLabel, and add it as a subview to your cell's content view:
在您的-initWithFrame:reuseIdentifier:方法中，您需要明确创建您的 noteTextLabel，并将其作为子视图添加到您单元格的内容视图中：
self.noteTextLabel = [[[UILabel alloc] initWithFrame: CGRectMake(0, 0, 200, 20)] autorelease];
[self.contentView addSubview: self.noteTextLabel];
Then this should work.
那么这应该有效。
Also, as a stylistic note, I would make the propertyfor noteTextLabel readonly, since you're only going to want to access it from outside the class, never set it.
此外，作为文体说明，我会将propertyfor noteTextLabel 设为只读，因为您只想从课程外部访问它，而不要设置它。
