无法在对话框片段中获得我的按钮上的指针

Question

我正在尝试构建一个简单的 DialogFragment，其中包含一个文本视图和两个按钮（发送和取消）。

我想在 textview 第一个为空时禁用该按钮，但我的代码中的 positiveButton 变量始终为空，并且出现以下异常：

 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setEnabled(boolean)' on a null object reference

这是代码：

public class SendFriendRequestFragment extends DialogFragment {
private TextView tvEmail = null;
Button positiveButton = null;

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    // Use the Builder class for convenient dialog construction
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());

    // Get the layout inflater
    final LayoutInflater inflater = getActivity().getLayoutInflater();

    final View layout = inflater.inflate(R.layout.fragment_send_friend_request, null);

    // Inflate and set the layout for the dialog
    // Pass null as the parent view because its going in the dialog layout
    builder.setView(layout)
            .setTitle("Send request")
            .setPositiveButton(R.string.send, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    String email = tvEmail.getText().toString().trim();

                    if (validateInput()) {
                        SendFriendRequest(getActivity(), email);
                    } else {
                        Toast.makeText(getActivity(), "Request cannot be sent", Toast.LENGTH_LONG).show();
                        return;
                    }

                }
            })
            .setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    // User cancelled the dialog
                }
            });

    Dialog dialog = builder.create();
    positiveButton = ((AlertDialog) dialog).getButton(AlertDialog.BUTTON_POSITIVE);

    positiveButton.setEnabled(false); // positiveButton is null and this call raises an exception !
    tvEmail = (TextView) layout.findViewById(R.id.email);
    tvEmail.addTextChangedListener(new InputTextWatcher(tvEmail));
    // Create the AlertDialog object and return it
    //return builder.create();
    return dialog;
}
// Other functions that use the two variables positiveButton and tvEmail ...
}

任何人都可以告诉我如何解决我的问题以及获取按钮指针和使用的布局中包含的视图的最佳方法是什么？

谢谢 ！

Answer 1

在显示Button之前不会实际创建正片Dialog。由于您在 中DialogFragment，因此您不会直接处理 上的show()呼叫Dialog。您可以在OnShowListener上设置AlertDialog，但Button在DialogFragment的onStart()方法中获取 可能更简单。

@Override
public void onStart() {
    super.onStart();

    positiveButton = ((AlertDialog) getDialog()).getButton(AlertDialog.BUTTON_POSITIVE);
    ...
}