GWT中的原生Javascript方法

Question

我的GWT Java类中有一个原生Javascript方法，但是我在从本地Javascript代码调用Java方法时遇到了困难。我试图尽可能密切地跟踪这，但我无法让它开始工作。我编译了它并在Firefox中运行它，错误控制台说“错误: this.lc不是一个函数”。我试着把所有的方法都改为公开的，但这似乎没有什么区别。我做错了什么？

package com.proprintsgear.design_lab.client;
...
public class ValueBox extends HorizontalPanel {
...
private void fireChange() {
    ...
}

private void increaseValue() {
    ...
}

private native void addNativeMouseWheelListener(String id) /*-{
    function mouseOverHandler(e) {
        $wnd.addEventListener("DOMMouseScroll", scrollWheelMove, false);
    }

    function mouseOutHandler(e) {
        $wnd.removeEventListener("DOMMouseScroll", scrollWheelMove, false);
    }

    function scrollWheelMove(e) {
        if ($wnd.event || $wnd.Event) {
            if (!e) e = $wnd.event;
            if (e.wheelDelta <= 0 || e.detail > 0 ) {
                $wnd.alert("DOWN");
            } else {
                this.@com.proprintsgear.design_lab.client.ValueBox::increaseValue()();
            }
            this.@com.proprintsgear.design_lab.client.ValueBox::fireChange()();
        }
    }

    var box=$doc.getElementById(id);
    box.addEventListener("mouseout",mouseOutHandler,false);
    box.addEventListener("mouseover",mouseOverHandler,false);
}-*/;

Answer 1

在我过去做过的所有代码中，我从来没有使用“this”来标识我的类，我已经通过了这个类。

改变这一点：

private native void addNativeMouseWheelListener(String id) /*-{
    function mouseOverHandler(e) {
        $wnd.addEventListener("DOMMouseScroll", scrollWheelMove, false);
    }

    function mouseOutHandler(e) {
        $wnd.removeEventListener("DOMMouseScroll", scrollWheelMove, false);
    }

    function scrollWheelMove(e) {
        if ($wnd.event || $wnd.Event) {
                if (!e) e = $wnd.event;
                if (e.wheelDelta <= 0 || e.detail > 0 ) {
                        $wnd.alert("DOWN");
                } else {
                        this.@com.proprintsgear.design_lab.client.ValueBox::increaseValue()();
                }
                this.@com.proprintsgear.design_lab.client.ValueBox::fireChange()();
        }
    }

    var box=$doc.getElementById(id);
    box.addEventListener("mouseout",mouseOutHandler,false);
    box.addEventListener("mouseover",mouseOverHandler,false);
}-*/;

对此：

private native void addNativeMouseWheelListener(ValueBox instance, String id) /*-{
    function mouseOverHandler(e) {
        $wnd.addEventListener("DOMMouseScroll", scrollWheelMove, false);
    }

    function mouseOutHandler(e) {
        $wnd.removeEventListener("DOMMouseScroll", scrollWheelMove, false);
    }

    function scrollWheelMove(e) {
        if ($wnd.event || $wnd.Event) {
                if (!e) e = $wnd.event;
                if (e.wheelDelta <= 0 || e.detail > 0 ) {
                        $wnd.alert("DOWN");
                } else {
                        instance.@com.proprintsgear.design_lab.client.ValueBox::increaseValue()();
                }
                instance.@com.proprintsgear.design_lab.client.ValueBox::fireChange()();
        }
    }

    var box=$doc.getElementById(id);
    box.addEventListener("mouseout",mouseOutHandler,false);
    box.addEventListener("mouseover",mouseOverHandler,false);
}-*/;

Answer 2

我找到了更好的方法。这与您在JavaScript中所做的类似，您在其中设置了"var that = this“。使用这种方法，您不必将其传递给listenForPostMessage()：

protected native void postMessage(String msg) /*-{
  $wnd.postMessage(msg, "*");
}-*/;

private final native void listenForPostMessage() /*-{
  var that = this;
  $wnd.addEventListener("message", function(msg) {
  that.@org.dartlang.gwtapplication.client.GwtApplication::onPostMessage(Ljava/lang/String;Ljava/lang/String;)(
    msg.data, msg.origin);
  });
}-*/;

private void onPostMessage(String data, String origin) {
  Label msgLabel = new Label();
  msgLabel.setText("GWT received a postMessage: Data: " +
      data + " Origin: " + origin);
  mainPanel.add(msgLabel);
}