GWT ValueChangeHandler并获得值 [英] GWT ValueChangeHandler and getting before value

问题描述

  String beforeValue =我想要获取我的textBox的值，然后更改其值。 ; 
 TextBox textBox = new TextBox（）; 
 textBox.addFocusHandler（new FocusHandler（）{
 
 public void onFocus（final FocusEvent event）{
 beforeValue = textBox.getText（）; 
 
 } 
}）; 
 textBox.addValueChangeHandler（new ValueChangeHandler< String>（）{
 
 public void onValueChange（final ValueChangeEvent< String> event）{
 System.out.println（ + beforeValue; 
 System.out.println（after value is+ textBox.getText（））; 
} 
}）; 
  

如上所述，我需要两个处理程序（ FocusHandler和ValueChangeHadler ）获得价值和价值之后。我的问题是如何通过一个Handler或其他简单而简单的方式获得它？我不想使用两个处理程序来获取它。任何建议，将不胜感激。

解决方案

您的想法（使用2个处理程序）是公平的，但它的越野车。我不认为可以以更好的方式完成。如果要使用单个处理程序，请使用两个处理程序创建自定义类包装。

这是代码。

  public abstract class MyValueChangeHandler< T>实现ValueChangeHandler< T> {
 
 T prevValue = null; 
 T value = null; 
 
 public MyValueChangeHandler（final ValueBoxBase< T> widget）{
 widget.addFocusHandler（new FocusHandler（）{
 public void onFocus（FocusEvent event）{
 prevValue = widget.getValue（）; 
} 
}）; 
} 
 
 @Override 
 public void onValueChange（ValueChangeEvent< T> event）{
 value = event.getValue（）; 
 onValueChange（value，prevValue）; 
 
 //或
 // onValueChange（event，prevValue）; 
 
 prevValue = value; 
} 
 
 public abstract void onValueChange（T value，T prevValue）; 
 
 //或
 // public abstract void onValueChange（ValueChangeEvent< T> event，T prevValue）; 
 
} 
  

您可以使用它作为

  TextBox box = new TextBox（）; 
 box.addValueChangeHandler（new MyValueChangeHandler< String>（box）{
 @Override 
 public void onValueChange（String value，String prevValue）{
 Window.alert（ + prevValue +CurrnetValue：
 + value）; 
} 
}）; 
  

I want to get values of my textBox before change its value and after changed its value.

String beforeValue = "";
TextBox textBox = new TextBox();
    textBox.addFocusHandler(new FocusHandler() {

        public void onFocus(final FocusEvent event) {
            beforeValue = textBox.getText();

        }
    });
    textBox.addValueChangeHandler(new ValueChangeHandler<String>() {

        public void onValueChange(final ValueChangeEvent<String> event) {
            System.out.println("Before value is " + beforeValue);
            System.out.println("After value is " + textBox.getText());
        }
    });

As above codes , I need two handlers (FocusHandler and ValueChangeHadler) to get before value and after value . My question is how can I get it by one Handler or another simple and easy way ? I don't want to use two handlers to get it. Any suggestions would be appreciated. Thanks in advance !

解决方案

Your idea(using 2 handlers) is fair enough but its buggy. I don't think it can be done in a better way. If you want to use a single handler, create a custom class wrapper using the two handlers.

Here is the code for you.

public abstract class MyValueChangeHandler<T> implements ValueChangeHandler<T> {

T prevValue = null;
T value = null;

public MyValueChangeHandler(final ValueBoxBase<T> widget) {
    widget.addFocusHandler(new FocusHandler() {
        public void onFocus(FocusEvent event) {
            prevValue = widget.getValue();
        }
    });
}

@Override
public void onValueChange(ValueChangeEvent<T> event) {
    value = event.getValue();
    onValueChange(value, prevValue);

    // or
    // onValueChange(event, prevValue);

    prevValue = value;
}

public abstract void onValueChange(T value, T prevValue);

// or
// public abstract void onValueChange(ValueChangeEvent<T> event, T prevValue);

}

And you can use it as,

TextBox box = new TextBox();
    box.addValueChangeHandler(new MyValueChangeHandler<String>(box) {
        @Override
        public void onValueChange(String value, String prevValue) {
            Window.alert("Prev Value : " + prevValue + " CurrnetValue: "
                    + value);
        }
    });

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