碎片，我在做什么错？

Question

So I am doing what this tutorial says. I've got a MainActivity with a navigation drawer.

This is my MainActivity.java

package nl.broekhin.magizon;


import android.app.Activity;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.design.widget.Snackbar;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;

import layout.LoginFragment;
import layout.RoosterFragment;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);




        LoginFragment loginFragment = new LoginFragment();
        RoosterFragment roosterFragment = new RoosterFragment();

        getSupportFragmentManager().beginTransaction()
                .add(R.id.fragment_container, loginFragment).commit();
    }



    public interface OnFragmentInteractionListener {
        //public void onFragmentMessage(String TAG, Object data);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_camera) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_manage) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }


}

This is my content_main.xml :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="nl.broekhin.magizon.MainActivity"
    tools:showIn="@layout/app_bar_main">

    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />


</RelativeLayout>

However, when I try to launch this, I get an error.

java.lang.RuntimeException: Unable to start activity ComponentInfo{nl.broekhin.magizon/nl.broekhin.magizon.MainActivity}: java.lang.RuntimeException: nl.broekhin.magizon.MainActivity@3e4143c must implement OnFragmentInteractionListener

Answer 1

Have you added a piece of code somewhere which checks if MainActivity is instance of OnFragmentInteractionListener?

If you want to communicate between Activity and Fragment, your activity needs to implement the interface Fragment defines to require.

In your case in your MainActivity after your class definition:

Class MainActivity extends Activity {

you should make it implement your OnFragmentInteractionListener interface this way:

Class MainActivity extends Activity implements OnFragmentInteractionListener {

After implementing the interface, you're required to implement the methods the interface defines, which you'll IDE will guide you how to do.

Answer 2

In your LoginFragment you are doing somewhere the following casting,

(OnFragmentInteractionListener)getActivity()

However your MainActivity doesn't implement the interface OnFragmentInteractionListener (even though you have defined it). The solution is simple. Change,

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

to

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener,OnFragmentInteractionListener {

Answer 3

Can you post your login fragment?

I guess the problem is that you're inflating the wrong layout file in your activity. Please check the inflated file. In your activity it says R.layout.activity_main but you named your xml as content_main.xml

Answer 4

I solved it!

Apparently, I had to use android.support.v4.app.Fragment; instead of android.app.Fragment; . This is the code I got it to work with:

protected void setFragment(Fragment fragment) {
    android.support.v4.app.FragmentTransaction t = getSupportFragmentManager().beginTransaction();
    t.replace(R.id.fragment_container, fragment);
    t.commit();
}

And to set it (from the nav bar onNavigationItemSelected() , you do this:

setFragment(new RoosterFragment());

I hope this helps others out with the same frustrating problem.

Answer 5

我想您必须在活动中实现OnFragmentIntractionListner接口。