android - IllegalStateException 如果尝试从 onActivityResult 显示对话框

Question

我正在开发一个需要用户启用蓝牙的应用程序。为此，一旦单击所需的按钮，就会抛出启用蓝牙的 Intent 。我正在使用以下代码:

public static final int ENABLE_BT = 1;

button.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        BluetoothAdapter mAdapter = BluetoothAdapter
                .getDefaultAdapter();
        if (!mAdapter.isEnabled()) {
            Intent enableBTIntent = new Intent(
                    BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
            startActivityForResult(enableBTIntent, ENABLE_BT);

        } 
    }

});

此外，如果用户未启用蓝牙，我希望显示一个对话框。这个类如下:

public class MessageDialog extends DialogFragment {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setMessage("Please enable Bluetooth to proceed")
                .setPositiveButton("Ok", new DialogInterface.OnClickListener() {

                    @Override
                    public void onClick(DialogInterface dialog, int which) {

                        dialog.dismiss();
                        // TODO Auto-generated method stub

                    }
                });

        return builder.create();
    }

}

onActivityResult()方法如下:

protected void onActivityResult(int requestCode, int resultCode,
            Intent intent) {
        if (requestCode == ENABLE_BT)
            if (resultCode == Activity.RESULT_CANCELED) {
                //button.setText("err");
                DialogFragment dialog = new MessageDialog();
                dialog.show(getSupportFragmentManager(), "Warning !");
            } 
}

问题是，一旦我不启用蓝牙，应用程序就会终止并出现 IllegalStateException。日志相关日志为:

java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=0, data=null} to activity {com.iskh.btchat.start/com.iskh.btchat.start.FirstActivity}: java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState

我无法理解显示 Dialog 为何是非法的。我已经检查过，只有当显示 Dialog 的代码存在时才会出现此错误。如果该代码被注释掉，那么该应用程序将按预期运行。我还测试了 Dialog。它在其他地方按预期显示。

谢谢。

Answer 1

将对话框的显示调用推迟到 FragmentActivity#onResumeFragments() 或 Activity#onPostResume() 而不是 onActivityResult

这在 "Failure Delivering Result " - onActivityForResult 中得到了回答

完整说明: http://www.androiddesignpatterns.com/2013/08/fragment-transaction-commit-state-loss.html