Exception 尝试在空对象引用上调用虚拟方法

有人能告诉我为什么我会犯这个错误吗？ 非常感谢

我正在测试Android，当文本使用以下Java类更改时，我正在努力显示一条消息：但我得到下面所述的Null异常。 我得到以下错误：

---

耶！发现了问题。 这很有趣，我在这里看过每一篇文章，都有类似的问题，但都没有解决

---

我的问题是-我为侦听器调用了错误的组件布局。我更新了R.layout.item_的详细信息，它成功了

布局中是否有部分删除的按钮？

public class ItemDetailFragment2 extends Fragment {
    private Item item;
    private EditText mEdit;
    private TextView mText;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    item = (Item) getArguments().getSerializable("item");


    mEdit = (EditText) mEdit.findViewById(R.id.tvBody);
    mText = (TextView) mText.findViewById(R.id.tvTitle);
    mText.setText("Welcome " + mEdit.getText().toString() + "!");
 }

 /* TextWatcher Implementation Methods */
public void beforeTextChanged(CharSequence s, int start, int count,
                              int after) {
}

 public void onTextChanged(CharSequence s, int start, int before, int  end) {

    Toast.makeText(getActivity(), mText.getText().toString(), Toast.LENGTH_LONG).show();
}

public void afterTextChanged(Editable s) {
}


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

    return view;

}

 java.lang.RuntimeException: Unable to start activity  ComponentInfo{com.example.my.helloworld/com.example.myProject.ItemDetailActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2329)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2389)
        at android.app.ActivityThread.access$900(ActivityThread.java:147)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1296)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at  com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java: 898)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)Caused  by: java.lang.NullPointerException: Attempt to invoke virtual  method 'void  android.widget.Button.setOnClickListener(android.view.View$OnClickListener' on a null object reference
        at  com.example.myproject.ItemDetailActivity.onCreate(ItemDetailActivity.java:131)
        at android.app.Activity.performCreate(Activity.java:5933)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2282)