java - SWT:获取即将从文本小部件中删除的字符数

Question

我正在验证来自某些 SWT 文本小部件的输入。
假设用户使用鼠标或Ctrl. + A选择了他自己插入到小部件中的文本的某些部分。等等，然后按删除；如何获取即将删除的字符数？我正在使用 SWT 验证事件进行输入验证。文档说 event.text 将给出“将插入的新文本。[...]”并且能够修改将被删除的文本，但我无法找到一种方法来获取金额将被删除的文本。

谷歌也没有给我答案。有人知道如何实现这一目标吗？

由于实际代码相当冗长，我不得不删除不必要的部分才能将其发布到此处:

该代码的目的是获取 32 个十六进制数字并允许复制/粘贴。

int len = 0;
// input is a SWT Text widget with initial text set to ""
input.addVerifyListener(new VerifyListener() {
    public void verifyText(VerifyEvent e){
        e.doit = false;
        int addit = 0;
        // do nothing when there are already 32 characters in the widget
        if (len == 32){
            return;
        }
        // allow Ctrl + v to paste
        if(((e.stateMask & SWT.CTRL) == SWT.CTRL) && (e.keyCode == 'v') && (len + e.text.length()) <= 32){
            e.doit = true;
            // here it works like a charm
            addit = e.text.length();
        }
        // allow deleting characters: Problem: deleting multiple characters at a time
        if (e.keyCode == SWT.BS || e.keyCode == SWT.DEL){
            e.doit = true;
            addit = ???;    // this is the problem: how many characters are deleted, when the key is pressed
        }
        // isHex is a function that checks, weather e.character is a hexadecimal digit
        if (isHex(e.character) || Character.isDigit(e.character) && len+1 <= 32){
            e.doit = true;
            addit = 1;
        } else if (e.keyCode != SWT.BS && e.keyCode != SWT.BS && ((e.stateMask & SWT.CTRL) != SWT.CTRL) && e.keyCode != 'v') {
            System.out.println(e.character + " is not valid");
            return;
        }
        len += addit;
        if (len == 32){
            somemethod();
        }
        // print how many characters are there the moment the user types or deletes them
        System.out.println((32 - len) + "chars");
    }});
}

Answer 1

您可以简单地比较原始文本和验证事件后用户修改的长度。听SWT.Verify并比较长度:

public static void main(String[] args)
{
    Display display = new Display();
    Shell shell = new Shell();
    shell.setText("StackOverflow");
    shell.setLayout(new FillLayout());

    final Text text = new Text(shell, SWT.BORDER);

    text.addListener(SWT.Verify, new Listener()
    {
        @Override
        public void handleEvent(Event e)
        {
            final String oldS = text.getText();
            final String newS = oldS.substring(0, e.start) + e.text + oldS.substring(e.end);

            int difference = oldS.length() - newS.length();

            if(difference > 0)
                System.out.println("User deleted " + difference + " characters");
            else if(difference < 0)
                System.out.println("User added " + Math.abs(difference) + " characters");
        }
    });

    shell.pack();
    shell.open();

    while (!shell.isDisposed())
    {
        if (!display.readAndDispatch())
        {
            display.sleep();
        }
    }
    display.dispose();
}