Question

我试图引用片段中的按钮并听取其点击次数。由于某种原因，它不断抛出NullPointerException，但我不知道为什么它为null。我知道答案可能非常简单明了但我无法在任何地方找到答案。

代码：

CardKeyboardFrag.java

package com.example.cribbage2;

import android.app.Activity;
import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;


public class CardKeyboardFrag extends android.support.v4.app.Fragment 
implements View.OnClickListener {

CardTransfer mCallback;

public interface CardTransfer {
    void onCardSelected(int card);
}

@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.card_keyboard_frag, container, false);

    //region buttonAssignments
    //this is where it happens
    Button one = (Button) getActivity().findViewById(R.id.buttonA);
    one.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View arg0) {
            buttonClicked(1);
        }
    });
    //endregion

    return view;
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);

    try {
        mCallback = (CardTransfer) context;
    } catch (ClassCastException e) {
        throw new ClassCastException(context.toString() + " must implement CardTransfer");
    }
}


@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.buttonA:
            buttonClicked(1);
            break;
        }
}

public void buttonClicked(int num){
    mCallback.onCardSelected(num);
}

}

这是xml：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                xmlns:app="http://schemas.android.com/apk/res-auto">


<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="16dp"
    android:text="Cards"
    android:textAlignment="center"
    android:textSize="30sp"/>

<GridLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentStart="true"
    android:layout_marginBottom="8dp"
    android:columnCount="3"
    android:rowCount="5">

    <Button
        android:id="@+id/buttonA"
        android:layout_width="120dp"
        android:layout_height="50dp"
        android:text="Ace"/>

</GridLayout>

</RelativeLayout>

提前致谢

空按钮参考

0 个答案: