text 片段沟通

Posted 2021-05-02

package com.example.android.android_me.ui;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.Toast;

import com.example.android.android_me.R;

// This activity is responsible for displaying the master list of all images
// Implement the MasterListFragment callback, OnImageClickListener
public class MainActivity extends AppCompatActivity implements MasterListFragment.OnImageClickListener{


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    // Define the behavior for onImageSelected
    public void onImageSelected(int position) {
        // Create a Toast that displays the position that was clicked
        Toast.makeText(this, "Position clicked = " + position, Toast.LENGTH_SHORT).show();
    }

}

package com.example.android.android_me.ui;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.GridView;

import com.example.android.android_me.R;
import com.example.android.android_me.data.AndroidImageAssets;


// This fragment displays all of the AndroidMe images in one large list
// The list appears as a grid of images
public class MasterListFragment extends Fragment {

    // Define a new interface OnImageClickListener that triggers a callback in the host activity
    OnImageClickListener mCallback;

    // OnImageClickListener interface, calls a method in the host activity named onImageSelected
    public interface OnImageClickListener {
        void onImageSelected(int position);
    }

    // Override onAttach to make sure that the container activity has implemented the callback
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);

        // This makes sure that the host activity has implemented the callback interface
        // If not, it throws an exception
        try {
            mCallback = (OnImageClickListener) context;
        } catch (ClassCastException e) {
            throw new ClassCastException(context.toString()
                    + " must implement OnImageClickListener");
        }
    }


    // Mandatory empty constructor
    public MasterListFragment() {
    }

    // Inflates the GridView of all AndroidMe images
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        final View rootView = inflater.inflate(R.layout.fragment_master_list, container, false);

        // Get a reference to the GridView in the fragment_master_list xml layout file
        GridView gridView = (GridView) rootView.findViewById(R.id.images_grid_view);

        // Create the adapter
        // This adapter takes in the context and an ArrayList of ALL the image resources to display
        MasterListAdapter mAdapter = new MasterListAdapter(getContext(), AndroidImageAssets.getAll());

        // Set the adapter on the GridView
        gridView.setAdapter(mAdapter);

        // Set a click listener on the gridView and trigger the callback onImageSelected when an item is clicked
        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                // Trigger the callback method and pass in the position that was clicked
                mCallback.onImageSelected(position);
            }
        });

        // Return the root view
        return rootView;
    }

}

1. Define an interface in the fragment class that triggers a callbacl=k in the host activity
2. Ovveride the onAttach to make sure that the container acrivity has implemented the callback.
3. Set a click listener in the gridView and trigger the callback when an item is clicked
4. In the host activity implemenet the interface 
5. Define the bahavior inside the callback method