如何在适配器类中调用 Main Activity 方法

Question

这是我的MainActivity，我在其中定义了dataRefresh 方法，该方法在从数据库中插入或删除数据时刷新适配器

public class MainActivity extends AppCompatActivity {
EditText phone, name;
ListView list;
MyDatabase db;
CustomAdapter ad;
ArrayList<contact> cont;
Button add;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    list=findViewById(R.id.list_item);
    db=new MyDatabase(this);
    cont=new ArrayList<>();
    cont=db.showData();
    ad=new CustomAdapter(this,cont;
    list.setAdapter(ad);
}


 public  void  dataRefresh(){
    cont.clear();
    cont.addAll(db.showData());
    ad.notifyDataSetChanged();
}

上面是dataRefresh方法

这是我的适配器类，我调用删除方法从数据库中删除数据

    public class CustomAdapter extends ArrayAdapter {
    ArrayList<contact> phnecontact;
    MyDatabase db;
    LinearLayout horizon;
    Context context;

    public CustomAdapter(@NonNull Context context, ArrayList<contact> 
    phonecontact) {
    super(context,R.layout.customlayout,phonecontact);
    this.context = context;
    this.phnecontact = phonecontact;
    }

    public contact getItem(int position) {
    return phnecontact.get(position);
   }

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

  @NonNull
  @Override
  public View getView(int position, View i, ViewGroup parent) {
    View view = 
  LayoutInflater.from(context).inflate(R.layout.customlayout, parent, 
  false);
    contact s1 = phnecontact.get(position);
    db=new MyDatabase(context);
    TextView name=view.findViewById(R.id.cmname);
    horizont=view.findViewById(R.id.horizontal);
    TextView number=view.findViewById(R.id.cmphone);
    ImageView sms=view.findViewById(R.id.message);
    ImageView call=view.findViewById(R.id.phone);
    ImageView photo=view.findViewById(R.id.cmphoto);
    number.setText(String.valueOf(s1.getPhone()));
    name.setText(s1.getName());
    horizont.setOnLongClickListener(v -> {
       AlertDialog.Builder builder=new AlertDialog.Builder(context);
       builder.setTitle("Are you sure to delete");
       builder.setPositiveButton("yes", new 
       DialogInterface.OnClickListener() {
           @Override
           public void onClick(DialogInterface dialog, int which) {
               int i =db.Deletioncontact(s1.getPhone());

我想在if条件之后调用Mainactivity的dataRefresh方法

               if(i==1)
               {

                   Toast.makeText(context, "contact is deleted", 
      Toast.LENGTH_SHORT).show();
               }
               else
               {
                   Toast.makeText(context, "contact not deleted", 
  Toast.LENGTH_SHORT).show();
               }
           }
       });

如果我使用 Mainactivity 的对象调用此方法，那么我的应用程序将崩溃

Answer 1

除了在mainActivity 中调用方法之外，还有一些可以改进的地方。

您不必在适配器中传递context，要在getView() 方法中使用，您可以从parent viewGroup 获取上下文

@Override
  public View getView(int position, View i, ViewGroup parent) {
    View view = 
  LayoutInflater.from(parent.getContext()).inflate(R.layout.customlayout, parent, 
  false);

您可以将所有clickListeners 和longClickListeneners 逻辑移动到activity，并使用interface 来触发这些方法。这样，您的适配器类将与您的activity 松散耦合，您也可以在另一个activity 或fragment 中使用此adapter。

在您的适配器类中创建clickInterface

public interface ClickListeners {
     public void onItemlongClickListener(int phone);
}

现在在你的活动中覆盖这个interface

public class MainActivity extends AppCompatActivity implements CustomAdapter.ClickListener{
    //

    @Override
    protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         //
         ad = new CustomAdapter(this, cont); // pass interface instance to the adapter
         //
    }

    @Override
    public void onItemlongClickListener(int phone) {
        // add your dialog confirmation 
        // and item deletion code here
    }

}

更改CustomAdaper构造函数以获取接口实例

public CustomAdapter(ClickListeners clickListeners, ArrayList<contact> 
    phonecontact) {
    super(context,R.layout.customlayout,phonecontact);
    this.clickListeners = clickListeners;
    this.phnecontact = phonecontact;
    }

当用户长按项目时触发onItemlongClickListener

horizon.setOnLongClickListener(v -> {
      clickListeners.onItemlongClickListener(s1.getPhone()); // call interface method
}

Answer 2

**在你的 onclick 方法中试试这个**

public void onClick(DialogInterface dialog, int which) {

int i =db.Deletioncontact(s1.getPhone());

Iterator<Integer> itr = numbers.iterator();
while(itr.hasNext()) { 
   Phone phone = itr.next(); 
   if (phone == s1.getPhone()) {  
      s1.remove(phone); 
   } 
}
notifyDataSetChange();
}