在 Swift 中的 UITextView 中添加占位符文本? [英] Add placeholder text inside UITextView in Swift?
问题描述
如何在 UITextView
中添加占位符,类似于您可以在 Swift
中为 UITextField
设置的占位符?
How can I add a placeholder in a UITextView
, similar to the one you can set for UITextField
, in Swift
?
推荐答案
已针对 Swift 4 更新
UITextView
本身没有占位符属性,因此您必须使用 UITextViewDelegate
方法以编程方式创建和操作一个占位符属性.我建议根据所需的行为使用下面的解决方案 #1 或 #2.
UITextView
doesn't inherently have a placeholder property so you'd have to create and manipulate one programmatically using UITextViewDelegate
methods. I recommend using either solution #1 or #2 below depending on the desired behavior.
注意:对于任一解决方案,将 UITextViewDelegate
添加到类并设置 textView.delegate = self
以使用文本视图的委托方法.
Note: For either solution, add UITextViewDelegate
to the class and set textView.delegate = self
to use the text view’s delegate methods.
解决方案 #1 - 如果您希望占位符在用户选择文本视图后立即消失:
Solution #1 - If you want the placeholder to disappear as soon as the user selects the text view:
首先将 UITextView
设置为包含占位符文本并将其设置为浅灰色以模仿 UITextField
的占位符文本的外观.在 viewDidLoad
中或在创建文本视图时执行此操作.
First set the UITextView
to contain the placeholder text and set it to a light gray color to mimic the look of a UITextField
's placeholder text. Either do so in the viewDidLoad
or upon the text view's creation.
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
然后当用户开始编辑文本视图时,如果文本视图包含占位符(即如果其文本颜色为浅灰色)清除占位符文本并将文本颜色设置为黑色以适应用户的输入.
Then when the user begins to edit the text view, if the text view contains a placeholder (i.e. if its text color is light gray) clear the placeholder text and set the text color to black in order to accommodate the user's entry.
func textViewDidBeginEditing(_ textView: UITextView) {
if textView.textColor == UIColor.lightGray {
textView.text = nil
textView.textColor = UIColor.black
}
}
然后当用户完成文本视图的编辑并且它辞去第一响应者的身份时,如果文本视图为空,则通过重新添加占位符文本并将其颜色设置为浅灰色来重置其占位符.
Then when the user finishes editing the text view and it's resigned as the first responder, if the text view is empty, reset its placeholder by re-adding the placeholder text and setting its color to light gray.
func textViewDidEndEditing(_ textView: UITextView) {
if textView.text.isEmpty {
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
}
}
<小时>
解决方案 #2 - 如果您希望占位符在文本视图为空时显示,即使文本视图被选中:
Solution #2 - If you want the placeholder to show whenever the text view is empty, even if the text view’s selected:
首先在viewDidLoad
中设置占位符:
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
textView.becomeFirstResponder()
textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)
(注意:由于 OP 希望在视图加载后立即选择文本视图,因此我将文本视图选择合并到了上述代码中.如果这不是您想要的行为并且您不希望在其上选择文本视图查看加载,去掉上面代码块的最后两行.)
(Note: Since the OP wanted to have the text view selected as soon as the view loads, I incorporated text view selection into the above code. If this is not your desired behavior and you do not want the text view selected upon view load, remove the last two lines from the above code chunk.)
然后利用shouldChangeTextInRange
UITextViewDelegate
方法,像这样:
Then utilize the shouldChangeTextInRange
UITextViewDelegate
method, like so:
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
// Combine the textView text and the replacement text to
// create the updated text string
let currentText:String = textView.text
let updatedText = (currentText as NSString).replacingCharacters(in: range, with: text)
// If updated text view will be empty, add the placeholder
// and set the cursor to the beginning of the text view
if updatedText.isEmpty {
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)
}
// Else if the text view's placeholder is showing and the
// length of the replacement string is greater than 0, set
// the text color to black then set its text to the
// replacement string
else if textView.textColor == UIColor.lightGray && !text.isEmpty {
textView.textColor = UIColor.black
textView.text = text
}
// For every other case, the text should change with the usual
// behavior...
else {
return true
}
// ...otherwise return false since the updates have already
// been made
return false
}
并且还实现了 textViewDidChangeSelection
以防止用户在占位符可见时更改光标的位置.(注意:textViewDidChangeSelection
在视图加载之前被调用,所以只有在窗口可见时才检查文本视图的颜色):
And also implement textViewDidChangeSelection
to prevent the user from changing the position of the cursor while the placeholder's visible. (Note: textViewDidChangeSelection
is called before the view loads so only check the text view's color if the window is visible):
func textViewDidChangeSelection(_ textView: UITextView) {
if self.view.window != nil {
if textView.textColor == UIColor.lightGray {
textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)
}
}
}
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