Passing an ArrayList via interface between 2 fragments

问题

Hey I try to pass an ArrayList with the Interface method between two Fragments in one activity. The logcat says there are no errors, but the item I added the ArrayListin the one Fragment is not shown in my Spinner in the other Fragment. I will post my whole code, so if you see my problem, it would be nice if you explain me the solution. Thanks in advance.

MainActivity.java

 package de.kwietzorek.fulcrumwebview;


import android.app.Activity;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity implements Callback {

    static WebView myWebView;
    Fragment AddServerFragment, WebViewFragment;
    ArrayList<String> server_name_list;

    @Override
    public ArrayList<String> getArrayListFromActivity() {

        WebViewFragment frag = (WebViewFragment) getSupportFragmentManager().findFragmentByTag("AddServerFragment");
        if (frag != null) {
            server_name_list = frag.getArrayListFromActivity();
        }
        return server_name_list;
    }

    /* Menu */
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.webview:
                getSupportFragmentManager().beginTransaction()
                        .replace(R.id.container, new WebViewFragment() {

                        })
                        .commit();
                return true;
            case R.id.add_server:
                getSupportFragmentManager().beginTransaction()
                        .replace(R.id.container, new AddServerFragment() {

                        })
                        .commit();
                return true;
            case R.id.menu_refresh:
                myWebView.reload();
                return true;
            default:
                return true;
        }
    }

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

        if (findViewById(R.id.container) != null) {
            if (savedInstanceState != null) {
                return;
            }
            AddServerFragment = new Fragment();
            WebViewFragment = new Fragment();
        }
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.container, new WebViewFragment() {

                })
                .commit();
    }

    /*WebView Fragment*/
    public class WebViewFragment extends Fragment {

        String selected;
        Spinner spinner;

        public WebViewFragment(){
        }

        private Callback callback;


        @Override
        public void onAttach(Activity activity) {
            super.onAttach(activity);
            callback = (Callback) activity;}

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

            /* WebView */
            myWebView = (WebView) view.findViewById(R.id.webView);
            myWebView.setWebViewClient(new WebC());
            WebSettings webSettings = myWebView.getSettings();

            /* JavaScript Enable */
            webSettings.setJavaScriptEnabled(true);

            /* Server Name Spinner */

            ArrayList<String> server_name_list = callback.getArrayListFromActivity();

            if (server_name_list != null) {

                spinner = (Spinner) view.findViewById(R.id.server_spinner);
                ;
                ArrayAdapter<String> server_adapter = new ArrayAdapter<String>(this.getActivity(),
                        android.R.layout.simple_spinner_item, server_name_list);

                server_adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                spinner.setAdapter(server_adapter);

                spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {

                    public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {

                        selected = parent.getItemAtPosition(pos).toString();

                        myWebView.loadUrl(selected);
                    }

                    public void onNothingSelected(AdapterView<?> parent) {

                    }
                });
            }
            return view;
        }

        public ArrayList<String> getArrayListFromActivity() {
            return server_name_list;
        }
    }

    /*Add Server Fragment*/
    public class AddServerFragment extends Fragment
            implements View.OnClickListener {

        @Override
        public void onClick(View view) {
        }

        public AddServerFragment(){
        }

        Button btn_back, btn_add;
        EditText server_ip, server_name;

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

            server_ip = (EditText) view.findViewById(R.id.edit_server_address);
            server_name = (EditText) view.findViewById(R.id.edit_server_name);

            btn_back = (Button) view.findViewById(R.id.btn_back);
            btn_back.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View view) {
                    getSupportFragmentManager().beginTransaction()
                            .replace(R.id.container, new WebViewFragment() {

                            })
                            .commit();
                }
            });

            btn_add = (Button) view.findViewById(R.id.btn_add);
            btn_add.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View view) {
                    String new_server_ip = null, new_server_name = null;

                    ArrayList<String> server_name_list = new ArrayList<>();
                    ArrayList<String> server_ip_list = new ArrayList<>();

                    new_server_ip = server_ip.getText().toString();
                    server_ip_list.add(new_server_ip);

                    new_server_name = server_name.getText().toString();
                    server_name_list.add(new_server_name);
                }
            });

            return view;
        }
    }

    /* WebView Client */
    public class WebC extends WebViewClient {

        @Override
        public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {

            super.onReceivedError(view, errorCode, description, failingUrl);

        }
    }
}

Callback.java

 package de.kwietzorek.fulcrumwebview;

import java.util.ArrayList;

public interface Callback {
        ArrayList<String> getArrayListFromActivity();
    }

回答1:

Each time you're adding something into the ArrayList that is used by some Adapter (in your case by adapter for the spinner) you have to call adapter.notifyDataSetChanged() on it. So you have to "tell" the WebViewFragment that it needs to refresh (call notifyDataSetChanged() on adapter) it's content each time you're adding something to ArrayList in your second fragment

来源：https://stackoverflow.com/questions/33725356/passing-an-arraylist-via-interface-between-2-fragments