Android Learning notes Actionbar as back to the top level

First, add the return icon to Actionbar:

Code:

@Overrideprotected voidonCreate (Bundle savedinstancestate) {Super. OnCreate (savedinstancestate);   Setcontentview (r.layout.settings); Issendmsg=(Switch) Findviewbyid (r.id.issendmessage); Iscall=(Switch) Findviewbyid (R.id.iscall); Data=(Initdataapp) getapplication ();  Issendmsg.setchecked (Data.issendmsg ());  Iscall.setchecked (Data.iscall ()); ActionBar ActionBar=Getactionbar (); Actionbar.setdisplayhomeasupenabled (true); //Actionbar.setlistnavigationcallbacks (adapter, callback);  }

Set available

To override the Onoptionsitemselected method:

@Override Public Booleanonoptionsitemselected (MenuItem item) {Switch(Item.getitemid ()) { CaseAndroid. R.id.home://Navutils.navigateupfromsametask (this);//onsaveinstancestate//This was called when the Home (UP) button is pressed//In the Action Bar.Intent parentactivityintent=NewIntent ( This, Mainactivity.class); Parentactivityintent.addflags (Intent.flag_activity_clear_top|intent.flag_activity_new_task);                       StartActivity (parentactivityintent);        Finish (); //onbackpressed ();   return true; }  return Super. onoptionsitemselected (item);}

This method can implement processing when the call is returned up.

Receive: Android. R.id.home There are several ways to handle this android.r.id.home, first comparing it:

  @Override  public  Span style= "Color:rgb (0, 0, 255); >boolean   onoptionsitemselected (MenuItem item) { switch   (Item.getitemid ()) { case   Android. R.id.home:navutils.navigateupfromsametask ( // onsaveinstancestate    return  true   return  super  Span style= "Color:rgb (0, 0, 0); >.onoptionsitemselected (item); }

When the test is rolled back, there is a loss of data to the previous activity. (test mode, add a edittext in a, then enter the data, click to jump into the bactivity, the use of up-level navigation will show the loss of data)

@Override Public Booleanonoptionsitemselected (MenuItem item) {Switch(Item.getitemid ()) { CaseAndroid. R.id.home:intent parentactivityintent=NewIntent ( This, Mainactivity.class); Parentactivityintent.addflags (Intent.flag_activity_clear_top|intent.flag_activity_new_task);            StartActivity (parentactivityintent);   Finish (); return true; }  return Super. onoptionsitemselected (item);}

The data is lost using the same intent method.

Later I looked at the source code, found to click on the phone's fallback button, triggered onbackpressed (); method, this method is to return the time axis of the previous activity, you can save the data.

 Public Boolean onoptionsitemselected (MenuItem item) {  switch  (Item.getitemid ()) {  case  Android. R.id.home:   onbackpressed ();    return true ;  }   return Super . onoptionsitemselected (item);}

However, when testing, it was found that this method only returns the previous one, not the logical designation, for example: A->b->c, return from C to A, if using onbackpressed (), then go back to B, so wrong. To this we can only use Navutils.navigateupfromsametask (this);//onsaveinstancestate, but we want to save the data in real time.

Next we will be the preservation of data processing, on-site protection!