ios - drawRect 方法不绘制

Question

我一直在使用 UITextField 的子类在我的文本字段末尾绘制一个“m3”字符串，但有些东西不起作用。我知道正在调用该方法，因为我已经使用 NSLog 对其进行了测试，我做错了什么？

我的类(class):

// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{

    NSString *strM3 = [[NSString alloc] initWithFormat:@" m³"];

    /// Make a copy of the default paragraph style
    NSMutableParagraphStyle *paragraphStyle = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
    /// Set line break mode
    paragraphStyle.lineBreakMode = NSLineBreakByTruncatingTail;
    /// Set text alignment
    paragraphStyle.alignment = NSTextAlignmentRight;

    NSDictionary *attributes = @{ NSFontAttributeName:[UIFont fontWithName:@"HelveticaNeue-Bold" size:12.0],
                                  NSParagraphStyleAttributeName:paragraphStyle};

    [strM3 drawInRect:rect withAttributes:attributes];

}

Answer 1

UITextField 在其自身之上绘制了很多东西。背景图将被所有这些东西掩盖。要对此进行测试，您可以以编程方式删除所有 subview 并查看您的“m3”是否出现。

for(UIView *subview in textField.subviews) [subview removeFromSuperview];

我认为您将不得不设置默认文本，然后在输入新字符时修改输入文本。设置一个 UITextViewDelegate 并重载函数 shouldChangeCharactersInRange:

- (BOOL) textField: (UITextField *)theTextField shouldChangeCharactersInRange: (NSRange)range replacementString: (NSString *)string {    
  //Do some string manipulation in here to remove the "m3", then add the user's input, then replace the "m3"
}