GWT - 从外部JavaScript调用实例方法 [英] GWT - Calling instance method from external javascript

问题描述

我们可以在GWT中使用$ entry方法来允许外部javascript执行java方法。
您可以在他们的文档中看到解释 https ：//developers.google.com/web-toolkit/doc/latest/DevGuideCodingBasicsJSNI？hl = fr＃calling

然而，这里的例子只有用静态方法。我试图为它写一个非静态方法，当我尝试调用它时，我得到一个异常：

  java.lang.ClassCastException：无法将com.google.gwt.core.client.JavaScriptObject $转换为mypackage.MyModule 
  

下面是我的代码：

  public native void setRefreshModuleCallback（）/ *  -  {
 $ wnd.refreshModule = $ entry（function（）{
 this。@ mypackage.MyModule :: refreshModuleJava（）; 
 alert（'test'）; 
}）; 
}  -  * /; 
 
 public void refreshModuleJava（）{
 logger.log（Level.WARNING，REFRESH）; 
} 
  

我发现非常有趣的是，alert被调用，我看到结果浏览器，但之前的调用不会执行。

你知道是否真的有可能做这种事吗？

解决方案

$ entry 不是关于调用java ，而是关于确保一些事情顺利进行在GWT中：异常被路由到 GWT.UncaughtExceptionHandler ，并通过 Scheduler＃scheduleEntry 和 Scheduler＃scheduleFinally 被正确调用。 您的问题是 this 。当函数被调用时，这个不是你的 MyModule 类（它很可能是 $ wnd object）。这就是为什么你链接的问题使用 var that = this 。这是关于范围。

您还需要实际调用方法，不仅仅引用它：在JSNI中，第一对parens用于形式参数（以消除重载），并且您需要另一对传递实际参数：。@ mypackage.MyModule :: refreshModuleJava（）（）。

There is this $entry method that we can use in GWT to allow external javascript to execute java methods. You can see the explanations in their documentation https://developers.google.com/web-toolkit/doc/latest/DevGuideCodingBasicsJSNI?hl=fr#calling

However, the example there is only with static methods. I'm trying to write it for a non-static method and when I try to call it, I get an exception :

java.lang.ClassCastException: Cannot cast com.google.gwt.core.client.JavaScriptObject$ to mypackage.MyModule

Here is my code :

public native void setRefreshModuleCallback() /*-{
    $wnd.refreshModule = $entry(function() {
        [e-mail]::refreshModuleJava();
        alert('test');
    });
}-*/;

public void refreshModuleJava() {
    logger.log(Level.WARNING, "REFRESH");
}

What I find very funny is that alert is called, I see the result in the browser, but the call just before is not performed.

Do you know if it's actually possible to do such thing ?

解决方案

$entry is not about calling java, it's about ensuring a few things go well in GWT: exceptions are routed to the GWT.UncaughtExceptionHandler, and commands scheduled via Scheduler#scheduleEntry and Scheduler#scheduleFinally are correctly called.

Your problem is the this. When the function is called, this is not your MyModule class (it's most probably the $wnd object). This is why the question you linked to uses var that = this. It's about scoping.

You also need to actually call the method, not only reference it: in JSNI, the first pair of parens are for the formal parameters (to disambiguate overloads), and you need another pair passing the actual arguments: [e-mail]::refreshModuleJava()().

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