Question

我绝望地尝试了互联网上的一切，以便能够打电话给我 thisIsAMethodJustToTryOutMyButton(View view)，当用户点击我的Delete Button MainActivity时，但无效。按钮没有反应。

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference

适配器类

public class Adapter extends BaseAdapter{

private ArrayList<item> items= new ArrayList<>();


public void addItemToListView(Item item){
    this.items.add(item);
}

public void deleteItem(int position){
    items.remove(position);
}

@Override
public Item getItem(int position) {
    return items.get(position);
}

@Override
public long getIdOfItem(int position) {
    return position;
}

@Override
public int getCount() {
    return items.size();
}

class ViewHolder {
    public TextView title, content;

    public ViewHolder(View view){
        title= (TextView) view.findViewById(R.id.title);
        content= (TextView) view.findViewById(R.id.content);
    }
}


@Override
public View getView(final int position, View convertView, ViewGroup parent) {

    ViewHolder viewHolder;

    if(null == convertView){
        LayoutInflater inflater = LayoutInflater.from(parent.getContext());
        convertView = inflater.inflate(R.layout.custom_row, parent, false);
        viewHolder = new ViewHolder(convertView);
        viewHolder.header.setTag(position);
        convertView.setTag(viewHolder);

    }
    else{
        viewHolder = (ViewHolder) convertView.getTag();
    }

    Item item= getItem(position);
    viewHolder.header.setText(item.title);
    viewHolder.bodyText.setText(item.content);
    return convertView;
}
}

MyDialogForDeletingAItem类

 public class MyDialogForDeletingAItem extends DialogFragment 
    implements View.OnClickListener {
    Button delete;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.deleteDialog, null);
    delete = (Button) view.findViewById(R.id.delete);
    delete.setOnClickListener(this);
    return view; }

@Override
public void onClick(View view) {
if (view.getId() == R.id.delete) {
MainActivity main = new MainActivity();
            main.thisIsAMethodJustToTryOutMyButton(view, //This is where the problem is... 
//I don't know what to pass in here);
}

MainActivity类

 public class MainActivity extends AppCompatActivity implements       
    AdapterView.OnItemLongClickListener, AdapterView.OnItemClickListener {
    Adapter adapter;
    ListView listView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.ListView);
        adapter= new Adapter();
        listView.setAdapter(adapter);
        listView.setOnItemLongClickListener(this);
        listView.setOnItemClickListener(this);

public void longItemClick(View view) {
    DialogFragment dialog = new MyDialogForDeletingAItem();
    dialog.show(this.getSupportFragmentManager(), "MyDialogForDeletingAItem");
    thisIsAMethodJustToTryOutMyButton(view);

}
  public void deleteRow(int position){
        adapter.delete(position);
        adapter.notifyDataSetChanged();

    }

    public void thisIsAMethodJustToTryOutMyButton(View view, int position){
deleteRow(position);
     Toast.makeText(MainActivity.this,"" + position, Toast.LENGTH_SHORT).show();
}


 <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="DELETE"
        android:id="@+id/delete" 
        android:clickable="true"
        android:layout_alignTop="@+id/edit"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_marginRight="102dp"
        android:layout_marginEnd="102dp" />


at se.example.android.myapplication.MainActivity.thisIsAMethodJustToTryOutMyButton
(MainActivity.java:100)
at se.example.android.myapplication.DeleteAndEdit.onClick(DeleteAndEdit.java:45)

Answer 1

在您需要使用已加载的活动实例时，onClick(View view)方法会创建MainActivity的新实例。

像这样打电话

@Override
public void onClick(View view) {
if (view.getId() == R.id.delete) {
      ((MainActivity) getActivity()).thisIsAMethodJustToTryOutMyButton(view);
}

Answer 2

您的deleteRow()方法应将View视为参数

public void deleteRow(View view)

public static final int onClick

在API级别4中添加此视图上下文中方法的名称   单击视图时调用。此名称必须与公众对应   只接受一个View类型参数的方法。例如，如果   你指定android：onClick =＆＃34; sayHello＆＃34;，你必须声明一个公共空白   sayHello（View v）您的上下文方法（通常是您的Activity）。

必须是字符串值，使用＆＃39; \;＆＃39;逃避诸如＆＃39; \ n＆＃39;等人物   或者＆＃39; \ uxxxx＆＃39;对于unicode角色。

这也可能是对资源的引用（在表单中）   ＆＃34; @ [package：] type：name＆＃34;）或theme属性（在表单中   ＆＃34;？[package：] [type：] name＆＃34;）包含此类型的值。

onClick

Answer 3

在您的MainActivity中，您在哪里引用thisIsAMethodJustToTryOutMyButton？尝试在xml文件中添加android:onClick="thisIsAMethodJustToTryOutMyButton"

从我的MainActivity调用方法

3 个答案: