私はすぐにこれに腹を立てるので、私を助けてください:
コードを実行すると、最初にloadNewPoint()が実行され、グローバル変数(allPointsAndPlaces)からのデータが表示されます。
ただし、(子クラスの)ボタンをクリックすると、同じメソッドloadNewPoint()によってallPointsAndPlacesのnullポインターが返されます。
この問題を解決するために、コード構造を元のメソッドから大幅に変更し、このメソッド(loadNewPoint())を親クラスに移動して、問題が解決するかどうかを確認しました。
親クラス:
public class CabbieApp implements EntryPoint {
private GetLocationsServiceAsync getAllLocationsService = GWT.create(GetLocationsService.class);
CabbiePoint[] allPointsAndPlaces;
PointsQuiz quiz;
/**
* Entry point method.
*/
public void onModuleLoad() {
//Get all the required data from DB
getAllPointsAndLocations();
}
private void loadAppPages(){
// Associate the Main panel with the HTML host page.
RootPanel rootPanel = RootPanel.get("pointsList");
quiz = new PointsQuiz();
rootPanel.setStyleName("GWTapp");
rootPanel.add(quiz.getMainPanel());
loadNewPoint();
}
private void getAllPointsAndLocations() {
// Initialize the service proxy.
if (getAllLocationsService == null) {
getAllLocationsService = GWT.create(GetLocationsService.class);
}
// Set up the callback object.
AsyncCallback<CabbiePoint[]> callback = new AsyncCallback<CabbiePoint[]>() {
public void onFailure(Throwable caught) {
System.out.println(caught.getMessage());
}
public void onSuccess(CabbiePoint[] result) {
//allPointsAndPlaces = result;
System.out.println(result.length);
allPointsAndPlaces = result;
loadAppPages();
}
};
// Make the call to the service.
getAllLocationsService.getLocations(callback);
}
void loadNewPoint(){
int r = Random.nextInt(allPointsAndPlaces.length);
quiz.CurrentPlace = allPointsAndPlaces[r].getPlaceName();
quiz.CurrentLocation = allPointsAndPlaces[r].getPlaceLocation();
quiz.point.setText(quiz.CurrentPlace);
quiz.location.setText(quiz.CurrentLocation);
quiz.location.setStyleName("invisibleText");
}
}
子クラス:
public class PointsQuiz extends CabbieApp{
VerticalPanel mainPanel = new VerticalPanel();
HorizontalPanel navigation = new HorizontalPanel();
TextBox point = new TextBox();
TextBox location = new TextBox();
Button showLocation = new Button("Show Location");
Button nextPoint = new Button("Next Point");
String CurrentPlace, CurrentLocation;
public PointsQuiz() {
// Assemble Add Stock panel.
navigation.add(showLocation);
navigation.add(nextPoint);
navigation.setCellHorizontalAlignment(nextPoint, HasHorizontalAlignment.ALIGN_RIGHT);
navigation.addStyleName("addPanel");
mainPanel.setSpacing(5);
mainPanel.setStyleName("body");
mainPanel.setVerticalAlignment(HasVerticalAlignment.ALIGN_MIDDLE);
mainPanel.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_CENTER);
// Assemble Main panel.
mainPanel.add(point);
point.setWidth("200px");
mainPanel.add(location);
location.setWidth("200px");
mainPanel.add(navigation);
navigation.setWidth("200px");
// Move cursor focus to the input box.
showLocation.setFocus(true);
// Listen for mouse events on the show location button.
showLocation.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
showCurrentLocation();}
});
// Listen for mouse events on the next point button.
nextPoint.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
loadNewPoint();
}
});
}
private void showCurrentLocation(){
location.setStyleName("visibleText");
}
public VerticalPanel getMainPanel() {
return mainPanel;
}
}