Question

我有一个自定义UITextField，以便我得到一个自定义的占位符文字颜色，如答案所示。但是，我还想在运行时更改占位符文本的颜色，因此我创建了一个属性。

// Overide the placholder text color
- (void) drawPlaceholderInRect:(CGRect)rect
{
    [self.placeholderTextColor setFill];
    [self.placeholder drawInRect:rect
                        withFont:self.font
                   lineBreakMode:UILineBreakModeTailTruncation
                       alignment:self.textAlignment];
}

- (void) setPlaceholderTextColor:(UIColor *)placeholderTextColor
{
    // To verify this is being called and that the placeholder property is set
    NSLog(@"placeholder text: %@", self.placeholder); 

    _placeholderTextColor = placeholderTextColor;
    [self setNeedsDisplay]; // This does not trigger drawPlaceholderInRect
}

问题是docs say I should not call drawPlaceholderInRect directly，而[self setNeedsDisplay];不起作用。有什么想法吗？

Answer 1

仅当文本字段实际包含占位符字符串时才调用drawPlaceholderInRect:方法。（默认不是这样）

尝试在Interface Builder中为文本字段设置占位符字符串还要确保在自定义类字段中设置子类。

<强>更新
我尝试重现问题中描述的问题，并遇到了这个问题。根据此Stack Overflow问题，这似乎是一个常见问题：https://stackoverflow.com/a/2581866/100848。

作为一种解决方法（至少在定位iOS＆gt; = 6.0时），您可以使用UITextField的attributionPlaceHolder：

NSMutableAttributedString* attributedString = [[NSMutableAttributedString alloc] initWithString:@"asdf"];
NSDictionary* attributes = @{NSForegroundColorAttributeName:[UIColor redColor]};
[attributedString setAttributes:attributes range:NSMakeRange(0, [attributedString length])];
[self.textField setAttributedPlaceholder:attributedString];

Answer 2

您也可以通过继承UITextField并覆盖drawPlaceholderInRect来实现这一目标

- (void) drawPlaceholderInRect:(CGRect)rect {
    if (self.useSmallPlaceholder) {
        NSDictionary *attributes = @{
                                 NSForegroundColorAttributeName : kInputPlaceholderTextColor,
                                 NSFontAttributeName : [UIFont fontWithName:kInputPlaceholderFontName size:kInputPlaceholderFontSize]
                                 };

        //center vertically
        CGSize textSize = [self.placeholder sizeWithAttributes:attributes];
        CGFloat hdif = rect.size.height - textSize.height;
        hdif = MAX(0, hdif);
        rect.origin.y += ceil(hdif/2.0);

        [[self placeholder] drawInRect:rect withAttributes:attributes];
    }
    else {
        [super drawPlaceholderInRect:rect];
    }
}

http://www.veltema.jp/2014/09/15/Changing-UITextField-placeholder-font-and-color/

如何调用drawPlaceholderInRect

2 个答案: