伙计们,我一直在努力寻找问题所在。终于我找到了卡住的地方。以下代码是我的项目的代码段,显示了唯一的问题。
那是我的EntryPoint类:
import com.google.gwt.canvas.client.Canvas;
import com.google.gwt.canvas.dom.client.Context2d;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.RootPanel;
import com.madmax.client.gameservice.GWTService;
import com.madmax.client.gameservice.GWTServiceAsync;
import com.madmax.client.resources.ResourceManager;
import com.madmax.client.resources.images.cards.LandCardResources;
public class AltEntryPoint implements EntryPoint {
public AltEntryPoint() {
}
public static GWTServiceAsync getService() {
return GWT.create(GWTService.class);
}
private final Canvas canvas= Canvas.createIfSupported();
private final Context2d ctx = canvas.getContext2d();
@Override
public void onModuleLoad() {
final ResourceManager resourceManager = new ResourceManager(1000, 1000);
Button b1 = new Button("Click", new ClickHandler() {
@Override
public void onClick(ClickEvent event) {
ctx.drawImage(resourceManager.getResourceCanvas().getCanvasElement(), 0, 0);
}
});
resourceManager.loadImgResource(LandCardResources.INSTANCE.getHellHorseKnight(), "knight", 0, 0);
resourceManager.loadImgResource(LandCardResources.INSTANCE.getMeadow(), "meadow", 150, 150);
canvas.setWidth(500 + "px");
canvas.setHeight(500 + "px");
canvas.setCoordinateSpaceWidth(500);
canvas.setCoordinateSpaceHeight(500);
RootPanel.get().add(resourceManager.getResourceCanvas());
ctx.drawImage(resourceManager.getResourceCanvas().getCanvasElement(), 0, 0);
RootPanel.get().add(canvas);
RootPanel.get().add(b1);
}
}
那是我的ResourceManeger类
import com.google.gwt.canvas.client.Canvas;
import com.google.gwt.canvas.dom.client.Context2d;
import com.google.gwt.dom.client.ImageElement;
import com.google.gwt.event.dom.client.LoadEvent;
import com.google.gwt.event.dom.client.LoadHandler;
import com.google.gwt.resources.client.ImageResource;
import com.google.gwt.user.client.ui.Image;
import com.google.gwt.user.client.ui.RootPanel;
public class ResourceManager {
private Canvas allImageHolderCanvas;
private Context2d allImageHolderContext;
public ResourceManager(int lengthDimension, int heightDimension) {
allImageHolderCanvas = Canvas.createIfSupported();
allImageHolderCanvas.setWidth(lengthDimension + "px");
allImageHolderCanvas.setHeight(heightDimension + "px");
allImageHolderCanvas.setCoordinateSpaceWidth(lengthDimension);
allImageHolderCanvas.setCoordinateSpaceHeight(heightDimension);
allImageHolderContext = allImageHolderCanvas.getContext2d();
}
public void loadImgResource(ImageResource resource, String name, double sx, double sy) {
final Image localImage = new Image(resource);
localImage.setVisible(false);
final String localName = name;
final double sxVal = sx;
final double syVal = sy;
localImage.addLoadHandler(new LoadHandler() {
@Override
public void onLoad(LoadEvent event) {
allImageHolderContext.drawImage(ImageElement.as(localImage.getElement()),
0, 0, localImage.getWidth(), localImage.getHeight(), sxVal, syVal, 1000, 1000);
}
});
RootPanel.get().add(localImage);
}
public void drawImageFromMetaDb(Context2d context, double sx, double sy, double sw,
double sh, double dx, double dy, double dw, double dh){
context.drawImage(allImageHolderCanvas.getCanvasElement(), sx, sy, sw, sh, dx, dy, dw, dh);
}
public Canvas getResourceCanvas(){
return this.allImageHolderCanvas;
}
}
一切都完美,除了一件事已经吓到我了。
ctx.drawImage(resourceManager.getResourceCanvas()。getCanvasElement(),0,0);
直到它在Handler内部调用后才起作用。
请向我解释我错了。非常感谢。
最佳答案
ctx.drawImage(resourceManager.getResourceCanvas().getCanvasElement(), 0, 0);
RootPanel.get().add(canvas);
除非将画布附加到文档(
canvas.isAttached()
,但是也可以附加到rootpanel上),否则无法在其上绘制。还必须设置大小,因为调整大小会对您的内容产生不利影响。
颠倒那些语句的顺序,它应该可以正常工作。加载处理程序起作用的原因是,在调用加载处理程序时,画布已被附加,因此可以被绘制。