Android - ClassCastException - BluetoothManager不能转换为android.bluetooth.BluetoothAdapter错误。

Question

现在，我编写的一些BluetoothAdapter代码有问题。我试图确定到底是什么导致了这个问题：

04-27 08:27:35.749    7802-7802/com.engineering.yellow E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.engineering.yellow, PID: 7802
java.lang.ClassCastException: android.bluetooth.BluetoothManager cannot be cast to android.bluetooth.BluetoothAdapter
        at com.engineering.yellow.fragment.SetDevicesFragment.isNotConnected(SetDevicesFragment.java:190)
        at com.engineering.yellow.bluetooth.BluetoothConnectionTask.onPostExecute(BluetoothConnectionTask.java:117)
        at com.engineering.yellow.bluetooth.BluetoothConnectionTask.onPostExecute(BluetoothConnectionTask.java:22)
        at android.os.AsyncTask.finish(AsyncTask.java:632)
        at android.os.AsyncTask.access$600(AsyncTask.java:177)
        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5579)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
        at dalvik.system.NativeStart.main(Native Method)

下面是我目前使用的代码：

@Override
public void isConnected() {
    Log.d(Constants.TAG, "Connected device");
    mNumDevicesConnected++;
    if (mNumDevicesConnected == mNumDevicesSelected) {
        if (mProgressDialog != null) {
            mProgressDialog.dismiss();
        }
        mBluetoothManager.startReading(getActivity());
        getActivity().setResult(Activity.RESULT_OK);
        getActivity().finish();
    }
}

@Override
public void isNotConnected() {
   BluetoothAdapter blutoothAdapter;

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
        appcontext = getActivity().getApplicationContext();
        Log.i("SetDevicesFragment", "Context Val:" + appcontext);
        appcontext = getActivity().getApplicationContext();
        blutoothAdapter = (BluetoothAdapter) appcontext.getSystemService(Context.BLUETOOTH_SERVICE);
    } else {
        blutoothAdapter = BluetoothAdapter.getDefaultAdapter();
    }

    Log.i("SetDevicesFragment", "SetDevicesFragment-BluetoothConnection-MACAddress: " + blutoothAdapter.getAddress());

    if (mProgressDialog != null) {
        mProgressDialog.dismiss();
    }

    //We check to make sure we still have activity access, in case the user attempted to go back
    //before we show the dialog.
    if (getActivity() != null) {
        AlertDialog.Builder builder = new AlertDialog.Builder(new ContextThemeWrapper(getActivity(), android.R.style.Theme_Holo_Dialog));
        builder.setTitle(R.string.device_connection_error_title).setMessage(R.string.device_connection_error_message)
                .setPositiveButton(R.string.auto_shutdown_dialog_session_ended_positive_button, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                });
        AlertDialog alertDialog = builder.create();
        breakExistingConnections();
        alertDialog.show();
    }
}

这是导致此ClassCastException的代码行：

blutoothAdapter = (BluetoothAdapter) appcontext.getSystemService(Context.BLUETOOTH_SERVICE);

是什么导致了这个问题？任何帮助都将不胜感激。

Answer 1

例外情况是，Context.getSystemService(Context.BLUETOOTH_SERVICE)返回的是BluetoothManager，而不是BluetoothAdapter。

要获得适配器，请使用BluetoothManager.getAdapter()

Answer 2

我在这里引用正式文件：

要获得表示本地蓝牙适配器的BluetoothAdapter，在JELLY_BEAN_MR1和更低级别上运行时，调用静态getDefaultAdapter()方法；在JELLY_BEAN_MR2和更高级别上运行时，使用BLUETOOTH_SERVICE通过getSystemService(String)检索它。

Answer 3

appcontext.getSystemService(Context.BLUETOOTH_SERVICE)返回类型为BluetoothManager的对象。您正在尝试将该对象声明为投射，而不是将其声明为BluetoothAdapter，这在本例中是不可能的，因此出现了错误。幸运的是，您可以从管理器获得适配器。

要解决这个问题，只需更改以下内容：

blutoothAdapter = (BluetoothAdapter) appcontext.getSystemService(Context.BLUETOOTH_SERVICE);

对此：

blutoothAdapter = ((BluetoothManager) appcontext.getSystemService(Context.BLUETOOTH_SERVICE)).getAdapter();