Question

我在gwt中玩过一段时间的历史，因为我打算在我当前的项目中实现它，所以我创建了一个小的演示项目，只是为了看它是如何工作的并做一些练习。因此，由于某些原因它不起作用。这是代码 - 非常简单的后退和前进。

这是iframe

<iframe id="__gwt_historyFrame" style="width:0;height:0;border:0"></iframe>

然后是切入点

public class EntryPoint implements com.google.gwt.core.client.EntryPoint {

private FirstPanel panel;

public void onModuleLoad() {

  ContentPanel panel = ContentPanel.getInstance();
  panel.setContent(FirstPanel.getInstance());
  RootPanel.get().add(panel);

}
}

和3个单例形式，正在加载表单的内容和2个表单。

public class ContentPanel extends Composite
{
private static ContentPanel instance;
private static VerticalPanel panel = new VerticalPanel();
private ContentPanel()
{
  initWidget(panel);
}

public void setContent(Widget widget)
{
  panel.clear();
  panel.add(widget);
}
public static ContentPanel getInstance()
{
   if(instance == null)
     return instance = new ContentPanel();
   else
     return instance;
}
}

和..

public class FirstPanel extends  Composite implements HistoryListener {

private static FirstPanel instance;
private VerticalPanel panel;

public FirstPanel() {

  History.addHistoryListener(this);

  panel = new VerticalPanel();
  panel.setStyleName("panelstyle");

  Button button2 = new Button("Next page");
  button2.addClickHandler(new ClickHandler()
  {
    public void onClick(ClickEvent event)
    {
      History.newItem("second_page");
    }
  });
  panel.add(button2);
  initWidget(panel);
}

public static FirstPanel getInstance()
{
  if(instance == null)
    return instance = new FirstPanel();
  else
    return instance;
}

public Widget getWidget() {
  return panel;
}

public void onHistoryChanged(String historyToken) {
 if(historyToken.equalsIgnoreCase("second_page"))
   ContentPanel.getInstance().setContent(SecondPanel.getInstance());
}

}

和最后但并非最不重要：））

    public class SecondPanel extends Composite  implements HistoryListener
    {
    private static SecondPanel instance;
    public SecondPanel()
    {
      History.addHistoryListener(this);
      VerticalPanel verticalPanel = new  VerticalPanel();
      TextBox firstnameBox = new TextBox();
      TextBox lastnameBox = new TextBox();
      Button submitButton = new Button("Click");

      verticalPanel.add(firstnameBox);
      verticalPanel.add(lastnameBox);
      verticalPanel.add(submitButton);

      submitButton.addClickHandler(new ClickHandler()
      {
        public void onClick(ClickEvent event)
        {
          History.newItem("first_panel");
          alert("You are in second panel");
        }
      });
      initWidget(verticalPanel);
    }

    public static SecondPanel getInstance()
{
    if(instance == null)
      return instance = new SecondPanel();
    else
      return instance;
}
    public void onHistoryChanged(String historyToken)
    {
      if(historyToken.equalsIgnoreCase("first_panel"))
        ContentPanel.getInstance().setContent(FirstPanel.getInstance());
    }
    }

问题是我单击FirstPanel中的按钮并加载了SecandPanel然后在浏览器中按“Back”不执行任何操作。在onHistoryChanged方法中，param historyToken为空字符串，不应该是堆栈中的值（ first_page）？

如果有人发现问题或解释我在哪里犯错误，我将不胜感激。

由于

Answer 1

在第一页加载时，您手动调用onHistoryChanged(INIT_STATE)。这不会改变历史。替换为：

public FirstPanel() {

    History.addHistoryListener(this);
    String token = History.getToken();
    if (token.length() == 0) {
        History.newItem(INIT_STATE);
    } else {
        History.fireCurrentHistoryState();
    }

    .. rest of code

更好的做法是仅在最顶层的面板（EntryPoint或ContentPanel）中注册历史侦听器History.addHistoryListener(..)，并根据历史记录切换面板。

历史GWT演示 - 不起作用

1 个答案: