如何子类化UITextField并覆盖drawPlaceholderInRect以更改占位符颜色

问题描述

我有一个3 UITextField ，并设置了占位符文本。在其中一个 UITextField 我希望占位符文本为红色。

I have a 3 UITextField with placeholder text set. On one of the UITextField I want the placeholder text to be red.

现在谷歌搜索后，最好的方法是将UITextField子类化并覆盖 drawPlaceholderInRect 。

Now after googling it seems the best way to do this is to subclass UITextField and override drawPlaceholderInRect.

如何进行子类化和覆盖 drawPlaceholderInRect ？我没有找到任何代码示例或教程，我是Objective-c和iOS开发的新手，所以发现它很难解决。

How do I go about subclassing and overriding drawPlaceholderInRect? I've not found any code examples or tutorials on this and I'm new to objective-c and iOS development so finding it tricky to work it out.

答案：

创建一个名为 CustomUITextFieldPlaceholder 的新Objective-c类，其子类为的UITextField 。在 CustomUITextFieldPlaceholder.m 中输入以下代码

Created a new objective-c class called CustomUITextFieldPlaceholder which subclassed UITextField. In CustomUITextFieldPlaceholder.m put the following code

 @implementation CustomUITextFieldPlaceholder

- (void)drawPlaceholderInRect:(CGRect)rect {
    // Set colour and font size of placeholder text
    [[UIColor redColor] setFill];
    [[self placeholder] drawInRect:rect withFont:[UIFont systemFontOfSize:12]];
}

@end

在你的实施中实现上述目的project

To implement the above in your project

#import "CustomUITextFieldPlaceholder.h"

和

IBOutlet CustomUITextFieldPlaceHolder *txtName;

注意：这有效，我相信是正确的做法，但我还没有完全测试过。希望这个例子在我的情况下帮助其他人。

编辑：

已更改

[[UIColor redColor] setFill];

[[UIColor colorWithRed:255.0 green:0.0 blue:0.0 alpha:0.7] setFill];

因此我可以将不透明度设置为70％以模仿默认占位符。

So that I could set the opacity to 70% to mimic default placeholder.

推荐答案

要回答具体问题，这就是子类化的工作原理：

To answer you specific question, this is how subclassing works:

// CustomTextField.h
@interface CustomTextField : UITextField {
}
@end

以下是如何覆盖方法：

@implementation
- (CGRect)placeholderRectForBounds:(CGRect)bounds {
    return CGRectMake(x,y,width,height);
}
@end

但我不认为这是你的方法想要覆盖。我认为这就是你要找的东西：

However I don't think that's the method you want to override. I think this is what you're looking for:

@implementation
- (void)drawPlaceholderInRect:(CGRect)rect {
    // Your drawing code.
}
@end

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