SWT Text控件输入指定范围数字

此方法允许Text内为空，避免无法回退修改。

private void setTextRange(Text text, int min, int max) {
		text.addVerifyListener(new VerifyListener() {
			@Override
			public void verifyText(VerifyEvent e) {
				Text text = (Text) e.getSource();
				final String oldStr = text.getText();
				String newStr = oldStr.substring(0, e.start) + e.text + oldStr.substring(e.end);
				boolean isValid = true;
				try {
					if (newStr.equals("")) {
						isValid = true;
					} else {
						int n = Integer.parseInt(newStr);
						if (n < min || n > max) {
							isValid = false;
						}
					}
				} catch (NumberFormatException ex) {
					isValid = false;
				}
				if (!isValid) {
					e.doit = false;
				}
			}
		});
	}