Question

我正在尝试构建一个简单的DialogFragment，它包含一个textview和两个按钮（发送和取消）。

我想在textview第一次为空时禁用该按钮，但我的代码中的positiveButton变量始终为null并且我得到以下异常：

 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 ...
}

有人可以告诉我如何解决我的问题以及获取按钮和使用的布局中包含的视图指针的最佳方法是什么？

谢谢！

Answer 1

在显示Button之前，实际上不会创建正Dialog。由于您使用的是DialogFragment，因此您无法直接处理show()上的Dialog来电。您可以在OnShowListener上设置AlertDialog，但在Button的{{1}}方法中获取DialogFragment可能更简单。

onStart()

在对话框片段中无法在我的按钮上获得指针

1 个答案: