使用Java导入强制类

Question

在构建我的应用程序时，我注意到当我在MainActivity（.java）中导入任何Java util时，我的应用程序强制关闭。

最初的是这一个：

package com.ivancristina.navigazione;

import android.content.Context;
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.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.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.LinearLayout;


public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("");

        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);
    }

    @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_formule) {

            LinearLayout mainLayout = (LinearLayout) findViewById(R.id. main_container);
            LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View layout = inflater.inflate(R.layout.content_formule, null);
            mainLayout.removeAllViews();
            mainLayout.addView(layout);

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

            LinearLayout mainLayout = (LinearLayout) findViewById(R.id. main_container);
            LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View layout = inflater.inflate(R.layout.content_esempi, null);
            mainLayout.removeAllViews();
            mainLayout.addView(layout);

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

            LinearLayout mainLayout = (LinearLayout) findViewById(R.id. main_container);
            LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View layout = inflater.inflate(R.layout.content_main, null);
            mainLayout.removeAllViews();
            mainLayout.addView(layout);

        }

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

而java的那个是这个：

package com.ivancristina.navigazione;

import android.content.Context;
import android.content.Intent;
import android.net.Uri;
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.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.util.SparseBooleanArray;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.Toast;

import java.util.*;


public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

        private ImageView logo;
        private Button github;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        initialize();
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("");

        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);
    }

    private void  initialize() {
        logo = (ImageView) findViewById(R.id.logo);
        github = (Button) findViewById(R.id.github);


        logo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View _v) {
                showMessage("Non c'è nulla da fare qui, faggot");
            }
        });
        github.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View _v) {
                startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.github.com/ivancristina")));
            }
        });

    }

    // created automatically
    private void showMessage(String _s) {
        Toast.makeText(getApplicationContext(), _s, Toast.LENGTH_SHORT).show();
    }

    private int getRandom(int _minValue ,int _maxValue){
        Random random = new Random();
        return random.nextInt(_maxValue - _minValue + 1) + _minValue;
    }

    public ArrayList<Double> getCheckedItemPositionsToArray(ListView _list) {
        ArrayList<Double> _result = new ArrayList<Double>();
        SparseBooleanArray _arr = _list.getCheckedItemPositions();
        for (int _iIdx = 0; _iIdx < _arr.size(); _iIdx++) {
            if (_arr.valueAt(_iIdx))
                _result.add((double)_arr.keyAt(_iIdx));
        }
        return _result;
    }

    @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_formule) {

            LinearLayout mainLayout = (LinearLayout) findViewById(R.id. main_container);
            LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View layout = inflater.inflate(R.layout.content_formule, null);
            mainLayout.removeAllViews();
            mainLayout.addView(layout);

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

            LinearLayout mainLayout = (LinearLayout) findViewById(R.id. main_container);
            LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View layout = inflater.inflate(R.layout.content_esempi, null);
            mainLayout.removeAllViews();
            mainLayout.addView(layout);

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

            LinearLayout mainLayout = (LinearLayout) findViewById(R.id. main_container);
            LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View layout = inflater.inflate(R.layout.content_main, null);
            mainLayout.removeAllViews();
            mainLayout.addView(layout);

        }

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

我确定我的某些活动出了问题，无论如何，如果有人想看看项目的其余部分，这里有我的 content_main和content_formule，正如我所说的那样，没有Java就可以正常工作，但这样做无用。

Answer 1

（代表OP发布）。

错误是我的。

我在initialize();之后立即super.onCreate(savedInstanceState);。

之前移动它

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

解决了我的问题。