问题
I am now having an activity containing fragments
[1] , [2] , [3] , [4]
If pressing buttons , [3] , it can be redirected to [4]
I would like to implement the back button as shown follow..
when pressing back at [4] , it return to [3]
when pressing back at [3] , it return to [2]
when pressing back at [1] , the activity finishes();
When it comes to the current implementation, it finish the activity instead of popping up the Fragment. Would you please tell me what I should do or keep in mind ?
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if( keyCode==KeyEvent.KEYCODE_BACK)
{
finish();
}
return super.onKeyDown(keyCode, event);
}
回答1:
In your onCreate() in your activity housing your fragments add a backstack change listener like so:
fragmentManager.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
@Override
public void onBackStackChanged() {
List<Fragment> f = fragmentManager.getFragments();
Fragment frag = f.get(0);
currentFragment = frag.getClass().getSimpleName();
}
});
(Nb. my fragmentManager is declared global) Now every time you change fragment the currentFragment String will become the name of the current fragment. Then in the activities onBackPressed() you can control the actions of your back button as so:
@Override
public void onBackPressed() {
switch (currentFragment) {
case "FragmentOne":
// your code here
return;
case "FragmentTwo":
// your code here
return;
default:
fragmentManager.popBackStack();
// default action for any other fragment (return to previous)
}
}
I can confirm that this method works for me.
Update : Kotlin
override fun onBackPressed() {
when(supportFragmentManager.fragments[0].javaClass.simpleName){
"FragmentOne" -> doActionOne()
"FragmentTwo" -> doActionTwo()
else -> supportFragmentManager.popBackStack()
}
}
回答2:
This worked for me.
-Add .addToBackStack(null) when you call the new fragment from activity.
FragmentTransaction mFragmentTransaction = getFragmentManager()
.beginTransaction();
....
mFragmentTransaction.addToBackStack(null);
-Add onBackPressed() to your activity
@Override
public void onBackPressed() {
if (getFragmentManager().getBackStackEntryCount() == 0) {
this.finish();
} else {
getFragmentManager().popBackStack();
}
}
回答3:
Easiest way ever:
onResume():
@Override
public void onResume() {
super.onResume();
getView().setFocusableInTouchMode(true);
getView().requestFocus();
getView().setOnKeyListener(new View.OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_UP && keyCode == KeyEvent.KEYCODE_BACK) {
// handle back button's click listener
Toast.makeText(getActivity(), "Back press", Toast.LENGTH_SHORT).show();
return true;
}
return false;
}
});
}
Edit 1: If fragment having EditText.
private EditText editText;
onCreateView():
editText = (EditText) rootView.findViewById(R.id.editText);
onResume():
@Override
public void onResume() {
super.onResume();
editText.setOnKeyListener(new View.OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
editText.clearFocus();
}
return false;
}
});
getView().setFocusableInTouchMode(true);
getView().requestFocus();
getView().setOnKeyListener(new View.OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_UP && keyCode == KeyEvent.KEYCODE_BACK) {
// handle back button's click listener
Toast.makeText(getActivity(), "Back press", Toast.LENGTH_SHORT).show();
return true;
}
return false;
}
});
}
Note: It will work if you have EditText in fragment.
Done
回答4:
This is a working solution for me:
dialog.setOnKeyListener(new DialogInterface.OnKeyListener() {
@Override
public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
// DO WHAT YOU WANT ON BACK PRESSED
return true;
}
return false;
}
});
Edit: You can replace dialog with getView() for fragments.
回答5:
You can use this .. Worked for me..
It seems as though fragment [3] is not removed from the view when back is pressed so you have to do it manually!
First of all, dont use replace() but instead use remove and add separately. It seems as though replace() doesnt work properly.
The next part to this is overriding the onKeyDown method and remove the current fragment every time the back button is pressed.
@Override
public boolean onKeyDown(int keyCode, KeyEvent event)
{
if (keyCode == KeyEvent.KEYCODE_BACK)
{
if (getSupportFragmentManager().getBackStackEntryCount() == 0)
{
this.finish();
return false;
}
else
{
getSupportFragmentManager().popBackStack();
removeCurrentFragment();
return false;
}
}
return super.onKeyDown(keyCode, event);
}
public void removeCurrentFragment()
{
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
Fragment currentFrag = getSupportFragmentManager().findFragmentById(R.id.f_id);
}
回答6:
Try this simple solution:
In your activity implement onBackPressed
@Override
public void onBackPressed() {
if (getSupportFragmentManager().getBackStackEntryCount() > 1) {
getSupportFragmentManager().popBackStack();
} else {
finish();
}
}
This will work if you want to pop the top fragment on each back press. Note:- While adding fragment to activity always do add the transaction to back stack for this to work
回答7:
Still better solution could be to follow a design pattern such that the back-button press event gets propagated from active fragment down to host Activity. So, it's like.. if one of the active fragments consume the back-press, the Activity wouldn't get to act upon it, and vice-versa.
One way to do it is to have all your Fragments extend a base fragment that has an abstract 'boolean onBackPressed()' method.
@Override
public boolean onBackPressed() {
if(some_condition)
// Do something
return true; //Back press consumed.
} else {
// Back-press not consumed. Let Activity handle it
return false;
}
}
Keep track of active fragment inside your Activity and inside it's onBackPressed callback write something like this
@Override
public void onBackPressed() {
if(!activeFragment.onBackPressed())
super.onBackPressed();
}
}
This post has this pattern described in detail
回答8:
What I do in this cases is I implement the onBackPressed() function from the Activity:
@Override
public void onBackPressed() {
super.onBackPressed();
FragmentManager fm = getSupportFragmentManager();
MyFragment myFragment = (MyFragment) fm.findFragmentById(R.id.my_fragment);
if((myFragmen.isVisible()){
//Do what you want to do
}
}
How this works for you too.
回答9:
Solution for Pressing or handling back button in Fragment.
The way I solved my issue I am sure it will helps you too:
1.If you don't have any Edit Text-box in your fragment you can use below code
Here MainHomeFragment is main Fragment (When I press back button from second fragment it will take me too MainHomeFragment)
@Override
public void onResume() {
super.onResume();
getView().setFocusableInTouchMode(true);
getView().requestFocus();
getView().setOnKeyListener(new View.OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_UP && keyCode == KeyEvent.KEYCODE_BACK){
MainHomeFragment mainHomeFragment = new SupplierHomeFragment();
android.support.v4.app.FragmentTransaction fragmentTransaction =
getActivity().getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, mainHomeFragment);
fragmentTransaction.commit();
return true;
}
return false;
}
}); }
2.If you have another fragment named as Somefragment and it has Edit text-box then you can do it by this way.
private EditText editText;
Then In,
onCreateView():
editText = (EditText) view.findViewById(R.id.editText);
Then Override OnResume,
@Override
public void onResume() {
super.onResume();
editText.setOnKeyListener(new View.OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
editTextOFS.clearFocus();
getView().requestFocus();
}
return false;
}
});
getView().setFocusableInTouchMode(true);
getView().requestFocus();
getView().setOnKeyListener(new View.OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_UP && keyCode == KeyEvent.KEYCODE_BACK){
MainHomeFragment mainHomeFragment = new SupplierHomeFragment();
android.support.v4.app.FragmentTransaction fragmentTransaction =
getActivity().getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, mainHomeFragment);
fragmentTransaction.commit();
return true;
}
return false;
}
});
}
That's all folks (amitamie.com) :-) ;-)
回答10:
if you are using webview inside a fragment than use this in your onCreateView method
webView.setOnKeyListener(new View.OnKeyListener(){
@Override
public boolean onKey(View view, int i, KeyEvent keyEvent) {
if((i==KeyEvent.KEYCODE_BACK)&& webView.canGoBack()){
webView.goBack();
return true;
}
return false;
}
});
and import this class
import android.view.KeyEvent;
回答11:
You can use getFragmentManager().popBackStack() in basic Fragment to go back.
回答12:
You also need to check Action_Down or Action_UP event. If you will not check then onKey() Method will call 2 times.
getView().setFocusableInTouchMode(true);
getView().requestFocus();
getView().setOnKeyListener(new OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_DOWN) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
Toast.makeText(getActivity(), "Back Pressed", Toast.LENGTH_SHORT).show();
return true;
}
}
return false;
}
});
Working very well for me.
回答13:
Make sure to add the following:
if (event.getAction()!=KeyEvent.ACTION_DOWN)
return true;
in the onKey block of code to avoid the event calling twice.
回答14:
i use a methode to change fragments it has thw following code
getSupportFragmentManager().beginTransaction().setCustomAnimations(R.anim.enter, R.anim.exit, R.anim.pop_enter, R.anim.pop_exit).replace(R.id.content_frame, mContent, mContent.getClass().getSimpleName()).addToBackStack(null)
.commit();
and for the back button this .
@Override
public void onBackPressed() {
// note: you can also use 'getSupportFragmentManager()'
FragmentManager mgr = getSupportFragmentManager();
if (mgr.getBackStackEntryCount() == 1) {
// No backstack to pop, so calling super
finish();
} else {
mgr.popBackStack();
}
}
the important thing to note is i use 1 for checking getBackStackEntryCount this is because if you dont use it and use 0 user sees nothing for the last back button.
来源：https://stackoverflow.com/questions/18755550/fragment-pressing-back-button