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中添加一个占位符，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本质上不具有占位符属性，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.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:对于这两种解决方案，请将UITextViewDelegate添加到类中，然后将textView.delegate = self设置为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，然后将其设置为浅灰色，以模仿UITextField占位符文本的外观.在viewDidLoad中或在创建文本视图时进行.

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)，则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将其辞去为第一响应者时，如果文本视图为空，请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
    }
}

---

解决方案2 -如果希望占位符在文本视图为空时显示，即使选择了文本视图:

---

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希望在加载视图后立即选择文本视图，因此我将文本视图选择合并到了上面的代码中.如果这不是您想要的行为，并且您不希望在选择文本视图时查看负载，请从上述代码块中删除最后两行.)

(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，如下所示:

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的情况下更改光标的位置. (注意:textViewDidChangeSelection在视图加载之前被调用，因此，如果窗口可见，则仅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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