AsyncTask: ClassCastException: java.lang.Object[] 不能转换为 java.lang.String[] [英] AsyncTask: ClassCastException: java.lang.Object[] cannot be cast to java.lang.String[]

问题描述

在我的应用程序中，我为 gcm ccs(xmpp) 运行这些代码，代码显示以下错误 An error occurred while execution doinbackground.excute()这是代码:

In my application I run these code for gcm ccs(xmpp) and the code shows following error An error occurred while executing doinbackground.excute() This is the code:

sendTask = new AsyncTask<String, String, String>() {
    protected String doInBackground(String... title) {

        Bundle data = new Bundle();
        data.putString("ACTION", action);
        data.putString("CLIENT_MESSAGE", "Hello GCM CCS XMPP!");
        String id = Integer.toString(ccsMsgId.incrementAndGet());

        try {
            Log.d("RegisterActivity", "messageid: " + id);
            gcm.send(SENDER_ID + "@gcm.googleapis.com", id,
                     data);
            Log.d("RegisterActivity", "After gcm.send successful.");
        } catch (IOException e) {
            Log.d("RegisterActivity", "Exception: " + e);
            e.printStackTrace();
        }
        return "Sent message.";
    }

    protected void onPostExecute(String result) {
        sendTask = null;
        // tosat about the success in return
    }
};

sendTask.execute(null, null, null);

推荐答案

你的 sendTask 是如何声明的?我想它只是AsyncTask sendTask;，如果是，则将其更改为:

How is your sendTask declared? I suppose its simply AsyncTask sendTask;, if so then change it to:

AsyncTask<String, String, String> sendTask;

<小时>

这个异常的原因类似于下面代码中发生的那个:

---

The cause of this exception is similar to the one that occurs in below code:

Object arr1[] = new Object[] {null,null,null};
String arr2[] = (String[])arr1; // here java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;

Java 中的 VarArgs 是作为数组实现的，因此当您将 sendTask 声明为 AsyncTask 时，编译器将使用 new 调用您的 doInBackgroundString[]{null,null,null}，但是当你将它声明为 AsyncTask 然后 doInBackground 用 new Object[]{null> 调用,null,null}.

VarArgs in java are implemented as arrays, so when you declare sendTask as AsyncTask<String, String, String> then compiler will call your doInBackground with new String[]{null,null,null}, but when you declare it as AsyncTask then doInBackground is called with new Object[]{null,null,null}.

由于类型擦除，编译器会添加从 Object[] 到 String[] 的隐藏隐式转换.这是为了让以下代码正常工作:

Because of type erasure, compiler will add hidden implicit cast from Object[] to String[]. This is to allow code as below to work correctly:

  AsyncTask sendTask = ...;
  Object[] arg = new String[]{null,null,null};
  sendTask.execute(arg);

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