如何限制javafx文本字段的字符数量 [英] How to limit the amount of characters a javafx textfield

问题描述

我使用FXML来设置表单，但我需要在textfields中设置字符数限制。我怎么能做到这一点？

I´m using a FXML to set my form, but I need to set the limit of characters in textfields. How can I made this ?

推荐答案

这是我的限制文本字段长度的解决方案。
我不推荐使用监听器的解决方案（在文本属性或长度属性上），它们在所有情况下都不正常（对于我所看到的）。
我创建一个具有最大长度的HTML输入文本，并将其与JavaFX中的文本字段进行比较。在两种情况下，我都使用粘贴操作（Ctrl + V），取消操作（Ctrl + Z）具有相同的行为。这里的目标是在修改文本字段之前检查文本是否有效。
我们可以对数字文本字段使用类似的方法。

Here is my solution to limit the length of a textfield. I would not recommend solutions which use a listener (on text property or on length property), they do not behave correctly in all situations (for what I have seen). I create an HTML input text with a max length, and compare it to my textfield in JavaFX. I had the same behavior with paste operations (Ctrl + V), cancel operations (Ctrl + Z) in both cases. The goal here is to check if the text is valid BEFORE modifying the textfield. We could use a similar approach for a numeric text field.

import java.util.Objects;
import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.scene.control.TextField;   

public class LimitedTextField extends TextField {

    private final IntegerProperty maxLength;

    public LimitedTextField() {
        super();
        this.maxLength = new SimpleIntegerProperty(-1);
    }

    public IntegerProperty maxLengthProperty() {
        return this.maxLength;
    }

    public final Integer getMaxLength() {
        return this.maxLength.getValue();
    }

    public final void setMaxLength(Integer maxLength) {
        Objects.requireNonNull(maxLength, "Max length cannot be null, -1 for no limit");
        this.maxLength.setValue(maxLength);
    }

    @Override
    public void replaceText(int start, int end, String insertedText) {
        if (this.getMaxLength() <= 0) {
            // Default behavior, in case of no max length
            super.replaceText(start, end, insertedText);
        }
        else {
            // Get the text in the textfield, before the user enters something
            String currentText = this.getText() == null ? "" : this.getText();

            // Compute the text that should normally be in the textfield now
            String finalText = currentText.substring(0, start) + insertedText + currentText.substring(end);

            // If the max length is not excedeed
            int numberOfexceedingCharacters = finalText.length() - this.getMaxLength();
            if (numberOfexceedingCharacters <= 0) {
                // Normal behavior
                super.replaceText(start, end, insertedText);
            }
            else {
                // Otherwise, cut the the text that was going to be inserted
                String cutInsertedText = insertedText.substring(
                        0, 
                        insertedText.length() - numberOfexceedingCharacters
                );

                // And replace this text
                super.replaceText(start, end, cutInsertedText);
            }
        }
    }
}

经过测试使用JavaFX 8和Java 8u45

Tested with JavaFX 8 and Java 8u45

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