如何等待异步http结束后再继续？
在GWT中有什么方法可以等待异步调用完成吗？ 我需要响应才能继续（这是一个登录屏幕，因此成功意味着更改为实际游戏，失败意味着停留在登录屏幕中）。
这是调用：
private void execRequest(RequestBuilder builder)
{
try
{
builder.sendRequest(null, new RequestCallback()
{
public void onError(Request request, Throwable exception)
{
s = exception.getMessage();
}
public void onResponseReceived(Request request,
Response response)
{
s = response.getText();
}
});
} catch (RequestException e)
{
s = e.getMessage();
}
}
这是调用方法：`
public String check()
{
s = null;
RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, baseUrl
+ "check&user=" + user + "&password=" + password);
execRequest(builder);
return s;
}
我需要 check 方法来返回响应（或错误）而不是返回 null。
我尝试了一种脑死亡的解决方案：
while (s == null);
等待调用完成，但这只是在开发模式下破坏了页面。
（chrome说页面无响应，建议杀掉它）
In GWT is there any way to wait for asynchronous call to complete?
I need the response to continue (It's a login screen so succes means changing to the actual game and failure means staying in the login screen).
Here is the call:
private void execRequest(RequestBuilder builder)
{
try
{
builder.sendRequest(null, new RequestCallback()
{
public void onError(Request request, Throwable exception)
{
s = exception.getMessage();
}
public void onResponseReceived(Request request,
Response response)
{
s = response.getText();
}
});
} catch (RequestException e)
{
s = e.getMessage();
}
}
And here is the calling method:`
public String check()
{
s = null;
RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, baseUrl
+ "check&user=" + user + "&password=" + password);
execRequest(builder);
return s;
}
I need the check method to return the response (or error) and not to return null.
I tried the brain-dead solution of writing:`
while (s == null);
To wait for the call to finish but that just crushed the page in development mode.
(chrome said page is unresponsive and suggested to kill it)
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评论（2）
拥抱异步，而不是对抗它！
换句话说：使您的 check 方法也异步，传递回调参数而不是返回值；并将回调传递给
execRequest（只需用对回调的调用替换对s的每个赋值即可）。正如 Jai 所建议的那样，您不一定需要在应用程序范围的事件总线上触发事件：它有助于解耦，但这并不总是您需要/想要的。
Embrace asynchrony, don't fight it!
In other words: make your
checkmethod asynchronous too, passing a callback argument instead of returning a value; and pass a callback toexecRequest(simply replace every assignment toswith a call to the callback).You don't necessarily need to fire an event on an application-wide event bus, as Jai suggested: it helps in decoupling, but that's not always what you need/want.
您不应该以这种方式检查是否完成。这里的最佳设计实践是在登录异步调用完成时触发自定义事件。当您收到事件（通过事件总线）时，您将执行剩余的任务。
阅读 http://code.google.com/webtoolkit/articles/ mvp-architecture.html#events
You should not check for completion that way. The best design practice here is to fire a custom event when the login async call completes.. and when you receive the event (through the event bus) you do the remaining tasks.
read up on http://code.google.com/webtoolkit/articles/mvp-architecture.html#events