我是android开发的初学者，实际上我有一个带有Fragments的导航抽屉我的问题是当我从导航抽屉中的状态转到片段b时成功更新到片段b但是当从片段A转到片段B时通过on'backpressed'方法，抽屉项状态不更新/更改为片段A.请帮我解决这个问题。
这是我的主要活动代码：
public class MainActivity extends AbsRuntimePermission implements NavigationView.OnNavigationItemSelectedListener {
//, GoogleApiClient.OnConnectionFailedListener {
private static final int REQUEST_PERMISSION = 10;
private Toolbar toolBar;
private NavigationView navDrawer;
private DrawerLayout drawerLayout;
private ActionBarDrawerToggle drawerToggle;
private FirebaseAuth.AuthStateListener authListener;
private FirebaseAuth auth;
private View btnLogOut;
private int selectedItem;
private FirebaseDatabase mFirebaseDatabase;
private DatabaseReference myRef;
// private GoogleApiClient googleApiClient;
private FloatingActionButton fab;
private CoordinatorLayout coordinatorLayout;
private HomeFragment homeFragment=new HomeFragment();
final String TAG = this.getClass().getName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
coordinatorLayout = (CoordinatorLayout) findViewById(R.id.coordinatorLayout);
auth = FirebaseAuth.getInstance();
final FirebaseUser user = auth.getCurrentUser();
String userID = user.getUid();
// Check if no view has focus:
View view = this.getCurrentFocus();
if (view != null) {
InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(view.getWindowToken(), 0);
}
fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(MainActivity.this, Contact_FAB.class);
startActivity(intent);
}
});
FragmentTransaction tx = getSupportFragmentManager().beginTransaction();
tx.replace(R.id.main_content, homeFragment);
tx.commit();
final WebView webView = (WebView) findViewById(R.id.WV);
WebSettings webSettings = webView.getSettings();
webSettings.setJavaScriptEnabled(true);
webView.setWebViewClient(new WebViewClient() {
public void onPageStarted(WebView view, String url, Bitmap favicon) {
}
public void onPageFinished(WebView view, String url) {
// do your stuff here}
@Override
public void onReceivedError (WebView view,int errorCode, String description, String
failingUrl){
super.onReceivedError(view, errorCode, description, failingUrl);
}
});
webView.loadUrl("https://google.co.in");
requestAppPermissions(new String[] {
Manifest.permission.READ_CONTACTS,
Manifest.permission.READ_EXTERNAL_STORAGE,
Manifest.permission.WRITE_EXTERNAL_STORAGE
},
R.string.msg,REQUEST_PERMISSION);
toolBar =(Toolbar)
findViewById(R.id.app_bar);
setSupportActionBar(toolBar);
// If a notification message is tapped, any data accompanying the notification
// message is available in the intent extras. In this project the launcher
// intent is fired when the notification is tapped, so any accompanying data would
// be handled here. If you want a different intent fired, set the click_action
// field of the notification message to the desired intent. The launcher intent
// is used when no click_action is specified.
//
// Handle possible data accompanying notification message.
if(
getIntent().
getExtras() !=null)
{
for (String key : getIntent().getExtras().keySet()) {
String value = getIntent().getExtras().getString(key);
if (key.equals("AnotherActivity") && value.equals("True")) {
Intent intent = new Intent(this, AnotherActivity.class);
intent.putExtra("value", value);
startActivity(intent);
finish();
}
}
}
// subscribeToPushService();
drawerLayout =(DrawerLayout)
findViewById(R.id.drawer_layout);
navDrawer =(NavigationView)
findViewById(R.id.menu_drawer);
navDrawer.setNavigationItemSelectedListener(this);
drawerToggle =new
ActionBarDrawerToggle(this,drawerLayout, toolBar, R.string.drawer_open, R.string.drawer_close);
drawerLayout.setDrawerListener(drawerToggle);
drawerToggle.syncState();
selectedItem =savedInstanceState ==null?R.id.nav_item_1 :savedInstanceState.getInt("selectedItem");
}
@Override
public boolean onNavigationItemSelected (MenuItem menuItem){
menuItem.setChecked(true);
selectedItem = menuItem.getItemId();
Fragment fragment = null;
switch (selectedItem) {
case R.id.nav_item_1:
fragment = new HomeFragment();
break;
case R.id.nav_item_2:
fragment = new MicrosoftDskFragment();
break;
case R.id.nav_item_3:
fragment = new GoogleDskFragment();
break;
case R.id.nav_item_4:
fragment = new AppleDskFragment();
break;
case R.id.nav_item_5:
fragment = new OthersDskFragment();
break;
case R.id.nav_item_6:
fragment = new MobiSpecsFragment();
break;
case R.id.nav_item_8:
Intent intent = new Intent(MainActivity.this, About.class);
startActivity(intent);
break;
default:
break;
}
if (!DetectConnection.checkInternetConnection(MainActivity.this)) {
Toast.makeText(MainActivity.this, "Plz check your network connectivity", Toast.LENGTH_SHORT).show();
} else {
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.main_content, fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
}
}
drawerLayout.closeDrawer(GravityCompat.START);
return true;
}
boolean twice = false;
@Override
public void onBackPressed () {
DrawerLayout layout = (DrawerLayout) findViewById(R.id.drawer_layout);
if (layout.isDrawerOpen(GravityCompat.START)) {
layout.closeDrawer(GravityCompat.START);
} else {
if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
getSupportFragmentManager().popBackStack();
} else {
Log.d(TAG, "click");
if (twice == true) {
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
finish();
System.exit(0);
}
twice = true;
Log.d(TAG, "twice: " + twice);
//super.onBackPressed();
Toast.makeText(MainActivity.this, "Please Press Again To Exit", Toast.LENGTH_SHORT).show();
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
twice = false;
Log.d(TAG, "twice: " + twice);
}
}, 3000);
}
}
}
@Override
public boolean onKeyDown ( int keyCode, KeyEvent event){
if (event.getAction() == KeyEvent.ACTION_DOWN) {
switch (keyCode) {
case KeyEvent.KEYCODE_BACK:
homeFragment.OnKeyDown(keyCode);
return true;
}
}
return super.onKeyDown(keyCode, event);
}
@Override
public boolean onCreateOptionsMenu (Menu menu){
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return super.onCreateOptionsMenu(menu);
}
@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.profile) {
Intent intent = new Intent(MainActivity.this, Profile.class);
startActivity(intent);
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onSaveInstanceState (Bundle outState, PersistableBundle outPersistentState){
super.onSaveInstanceState(outState, outPersistentState);
outState.putInt("selectedItem", selectedItem);
}
@Override
public void onPermissionsGranted ( int requestCode){
//Do anything when permisson granted
// Toast.makeText(getApplicationContext(), "Permission granted", Toast.LENGTH_LONG).show();
}
/* @Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
}
*/
}
}
答案 0 :(得分：0)
当popBackStack()来自后堆栈的片段出现在屏幕上时，您需要侦听Back堆栈更改。
getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
@Override
public void onBackStackChanged() {
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.containerFrame);
if (fragment != null) {
// check for fragment and set the drawer state
if(fragment instanceof Frag1){
// set drawer state for 1
}else if(fragment instanceof Frag2){
// set drawer state for 2
}
}
}
});