我正在制作一个简单的应用程序，但收到错误，这是我的 MainActivity.java
package com.example.intawebapp.activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.design.widget.Snackbar;
import android.support.v4.app.Fragment;
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 android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import com.bumptech.glide.Glide;
import com.bumptech.glide.load.engine.DiskCacheStrategy;
import com.example.intawebapp.R;
import com.example.intawebapp.fragment.HomeFragment;
import com.example.intawebapp.fragment.NotificationsFragment;
import com.example.intawebapp.fragment.SettingsFragment;
import com.example.intawebapp.other.CircleTransform;
import com.example.intawebapp.fragment.PortalFragment;
import com.example.intawebapp.fragment.ESSFragment;
public class MainActivity extends AppCompatActivity {
WebView myWebView;
private NavigationView navigationView;
private DrawerLayout drawer;
private View navHeader;
private ImageView imgNavHeaderBg, imgProfile;
private TextView txtName, txtWebsite;
private Toolbar toolbar;
private FloatingActionButton fab;
// urls to load navigation header background image
// and profile image
private static final String urlNavHeaderBg = "http://example.com/nav-menu-header-bg.jpg";
private static final String urlProfileImg = "http://example.com/prof";
// index to identify current nav menu item
public static int navItemIndex = 0;
// tags used to attach the fragments
private static final String TAG_HOME = "home";
private static final String TAG_PORTAL = "portal";
private static final String TAG_ESS = "ess";
private static final String TAG_NOTIFICATIONS = "notifications";
private static final String TAG_SETTINGS = "settings";
public static String CURRENT_TAG = TAG_HOME;
// toolbar titles respected to selected nav menu item
private String[] activityTitles;
// flag to load home fragment when user presses back key
private boolean shouldLoadHomeFragOnBackPress = true;
private Handler mHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mHandler = new Handler();
drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
navigationView = (NavigationView) findViewById(R.id.nav_view);
fab = (FloatingActionButton) findViewById(R.id.fab);
// Navigation view header
navHeader = navigationView.getHeaderView(0);
txtName = (TextView) navHeader.findViewById(R.id.name);
txtWebsite = (TextView) navHeader.findViewById(R.id.website);
imgNavHeaderBg = (ImageView) navHeader.findViewById(R.id.img_header_bg);
imgProfile = (ImageView) navHeader.findViewById(R.id.img_profile);
myWebView = (WebView) findViewById(R.id.myWebView);
WebSettings webSettings = myWebView.getSettings();
webSettings.setJavaScriptEnabled(true);
myWebView.setWebViewClient(new MyWebViewClient());
// load toolbar titles from string resources
activityTitles = getResources().getStringArray(R.array.nav_item_activity_titles);
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();
}
});
// load nav menu header data
loadNavHeader();
// initializing navigation menu
setUpNavigationView();
if (savedInstanceState == null) {
navItemIndex = 0;
CURRENT_TAG = TAG_HOME;
loadHomeFragment();
}
}
/***
* Load navigation menu header information
* like background image, profile image
* name, website, notifications action view (dot)
*/
private void loadNavHeader() {
// name, website
txtName.setText("My Name");
txtWebsite.setText("www.example.com");
// loading header background image
Glide.with(this).load(urlNavHeaderBg)
.crossFade()
.diskCacheStrategy(DiskCacheStrategy.ALL)
.into(imgNavHeaderBg);
// Loading profile image
Glide.with(this).load(urlProfileImg)
.crossFade()
.thumbnail(0.5f)
.bitmapTransform(new CircleTransform(this))
.diskCacheStrategy(DiskCacheStrategy.ALL)
.into(imgProfile);
// showing dot next to notifications label
navigationView.getMenu().getItem(3).setActionView(R.layout.menu_dot);
}
/***
* Returns respected fragment that user
* selected from navigation menu
*/
private void loadHomeFragment() {
// selecting appropriate nav menu item
selectNavMenu();
// set toolbar title
setToolbarTitle();
// if user select the current navigation menu again, don't do anything
// just close the navigation drawer
if (getSupportFragmentManager().findFragmentByTag(CURRENT_TAG) != null) {
drawer.closeDrawers();
// show or hide the fab button
toggleFab();
return;
}
// Sometimes, when fragment has huge data, screen seems hanging
// when switching between navigation menus
// So using runnable, the fragment is loaded with cross fade effect
// This effect can be seen in GMail app
Runnable mPendingRunnable = new Runnable() {
@Override
public void run() {
// update the main content by replacing fragments
Fragment fragment = getHomeFragment();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.setCustomAnimations(android.R.anim.fade_in,
android.R.anim.fade_out);
fragmentTransaction.replace(R.id.frame, fragment, CURRENT_TAG);
fragmentTransaction.commitAllowingStateLoss();
}
};
// If mPendingRunnable is not null, then add to the message queue
if (mPendingRunnable != null) {
mHandler.post(mPendingRunnable);
}
// show or hide the fab button
toggleFab();
//Closing drawer on item click
drawer.closeDrawers();
// refresh toolbar menu
invalidateOptionsMenu();
}
private Fragment getHomeFragment() {
switch (navItemIndex) {
case 0:
// home
HomeFragment homeFragment = new HomeFragment();
return homeFragment;
case 1:
// portal
PortalFragment portalFragment = new PortalFragment();
return portalFragment;
case 2:
// ESS fragment
ESSFragment essFragment = new ESSFragment();
return essFragment;
case 3:
// notifications fragment
NotificationsFragment notificationsFragment = new NotificationsFragment();
return notificationsFragment;
case 4:
// settings fragment
SettingsFragment settingsFragment = new SettingsFragment();
return settingsFragment;
default:
return new HomeFragment();
}
}
private void setToolbarTitle() {
getSupportActionBar().setTitle(activityTitles[navItemIndex]);
}
private void selectNavMenu() {
navigationView.getMenu().getItem(navItemIndex).setChecked(true);
}
private class MyWebViewClient extends WebViewClient {
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
myWebView.loadUrl(url);
return true;
}
}
private void setUpNavigationView() {
//Setting Navigation View Item Selected Listener to handle the item click of the navigation menu
navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
// This method will trigger on item Click of navigation menu
@Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
//Check to see which item was being clicked and perform appropriate action
switch (menuItem.getItemId()) {
//Replacing the main content with ContentFragment Which is our Inbox View;
case R.id.home:
navItemIndex = 0;
CURRENT_TAG = TAG_HOME;
break;
case R.id.nav_portal:
navItemIndex = 1;
CURRENT_TAG = TAG_PORTAL;
break;
case R.id.nav_ess:
navItemIndex = 2;
CURRENT_TAG = TAG_ESS;
break;
case R.id.nav_notifications:
navItemIndex = 3;
CURRENT_TAG = TAG_NOTIFICATIONS;
break;
case R.id.nav_settings:
navItemIndex = 4;
CURRENT_TAG = TAG_SETTINGS;
break;
case R.id.nav_about_us:
// launch new intent instead of loading fragment
startActivity(new Intent(MainActivity.this, AboutUsActivity.class));
drawer.closeDrawers();
return true;
case R.id.nav_exit:
// launch new intent instead of loading fragment
startActivity(new Intent(MainActivity.this, ExitActivity.class));
drawer.closeDrawers();
return true;
default:
navItemIndex = 0;
}
//Checking if the item is in checked state or not, if not make it in checked state
if (menuItem.isChecked()) {
menuItem.setChecked(false);
} else {
menuItem.setChecked(true);
}
menuItem.setChecked(true);
loadHomeFragment();
return true;
}
});
ActionBarDrawerToggle actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.openDrawer, R.string.closeDrawer) {
@Override
public void onDrawerClosed(View drawerView) {
// Code here will be triggered once the drawer closes as we dont want anything to happen so we leave this blank
super.onDrawerClosed(drawerView);
}
@Override
public void onDrawerOpened(View drawerView) {
// Code here will be triggered once the drawer open as we dont want anything to happen so we leave this blank
super.onDrawerOpened(drawerView);
}
};
//Setting the actionbarToggle to drawer layout
drawer.setDrawerListener(actionBarDrawerToggle);
//calling sync state is necessary or else your hamburger icon wont show up
actionBarDrawerToggle.syncState();
}
@Override
public void onBackPressed() {
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawers();
return;
}
// This code loads home fragment when back key is pressed
// when user is in other fragment than home
if (shouldLoadHomeFragOnBackPress) {
// checking if user is on other navigation menu
// rather than home
if (navItemIndex != 0) {
navItemIndex = 0;
CURRENT_TAG = TAG_HOME;
loadHomeFragment();
return;
}
}
super.onBackPressed();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
// show menu only when home fragment is selected
if (navItemIndex == 0) {
getMenuInflater().inflate(R.menu.main, menu);
}
// when fragment is notifications, load the menu created for notifications
if (navItemIndex == 3) {
getMenuInflater().inflate(R.menu.notifications, 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_logout) {
Toast.makeText(getApplicationContext(), "Logout user!", Toast.LENGTH_LONG).show();
return true;
}
// user is in notifications fragment
// and selected 'Mark all as Read'
if (id == R.id.action_mark_all_read) {
Toast.makeText(getApplicationContext(), "All notifications marked as read!", Toast.LENGTH_LONG).show();
}
// user is in notifications fragment
// and selected 'Clear All'
if (id == R.id.action_clear_notifications) {
Toast.makeText(getApplicationContext(), "Clear all notifications!", Toast.LENGTH_LONG).show();
}
return super.onOptionsItemSelected(item);
}
// show or hide the fab
private void toggleFab() {
if (navItemIndex == 0)
fab.show();
else
fab.hide();
}
}
这是我的AboutUsActivity
package com.example.intawebapp.activity;
import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.example.intawebapp.R;
public class AboutUsActivity extends Fragment {
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
public AboutUsActivity() {
// Required empty public constructor
}
public static AboutUsActivity newInstance(String param1, String param2) {
AboutUsActivity fragment = new AboutUsActivity();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.activity_about_us, container, false);
}
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
// if (context instanceof OnFragmentInteractionListener) {
// mListener = (OnFragmentInteractionListener) context;
// } else {
// throw new RuntimeException(context.toString()
// + " must implement OnFragmentInteractionListener");
// }
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
public interface OnFragmentInteractionListener {
void onFragmentInteraction(Uri uri);
}
}
当我从菜单中选择“关于”时，我收到此错误
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.intawebapp, PID: 8170
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.intawebapp/com.example.intawebapp.activity.AboutUsActivity}: java.lang.ClassCastException: com.example.intawebapp.activity.AboutUsActivity cannot be cast to android.app.Activity
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.ClassCastException: com.example.intawebapp.activity.AboutUsActivity cannot be cast to android.app.Activity
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2538)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Application terminated.
我需要帮助来解决这个问题。感谢