[英]How to handle onBackPressed() in multiple fragment
我是Android初学者,正在开发一个应用程序,其中通过一个活动使用了多个片段。
private void displaySelectedScreen(int itemId) {
Fragment fragment = null;
switch (itemId) {
case R.id.nav_home:
fragment = new HomeFragment();
break;
case R.id.nav_attendance:
fragment = new AttendanceFragment();
break;
case R.id.nav_notification:
fragment = new NotificationFragment();
break;
case R.id.nav_event:
fragment = new EventFragment();
break;
case R.id.nav_fee:
fragment = new FeesFragment();
break;
case R.id.nav_news:
fragment = new NewsFragment();
break;
}
if (fragment != null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.frame_container, fragment);
ft.addToBackStack(null);
ft.commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
}
如果抽屉已经关闭,则使用onBackPressed()
方法关闭应用程序。 现在,如果当前片段为HomeFragment
且当前片段不是HomeFragment
那么我想关闭一个应用程序,然后替换为HomeFragment
。 我不知道是怎么回事?
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout)findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
closeApp();
}
}
您可以将标签添加到片段中。 这样,您只需要检查标签名称即可。
Fragment fragment = new Fragment();
getFragmentManager().beginTransaction()
.replace(R.id.FrameLayoutId,fragment,"TAG_NAME")
.addToBackStack("SOURCE_TAG_NAME").commit();
这是检查片段标记的方法,将其放在活动的closeApp()
方法或closeApp()
方法中
function void closeApp(){
Fragment fragment = getFragmentManager().findFragmentByTag("HomeActivity");
if (fragment != null) {
if(fragment.isVisible()){
HomeActivity.this.finish();
}
}
}
简单来说,只需转到HomeFragment.java
并编辑onBackPressed()
方法onBackPressed()
使用finish()
退出应用程序。
对于其他Fragment.java
,只需使用popBackStack()
函数,就可以在这里搜索: https : //developer.android.com/reference/android/app/FragmentManager.html#popBackStack()
在您的MainActivity类中,重写onBackPressed
并在其中显示对话框,如下所示:
@Override
public void onBackPressed() {
//show dialog box here
}
在每个Fragment
使用以下代码实现onResume()
方法:
@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){
//homefragment class name
Class fragmentClass = HomeFragment.class;
try {
Fragment fragment = (Fragment) fragmentClass.newInstance();
FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();
} catch (Exception e) {
e.printStackTrace();
}
return true;
}
return false;
}
});
}
在NavigationActivity中使用此代码onBackPressed()方法。 希望能解决您的问题。
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
Fragment f = getVisibleFragment();// to get which fragment now
if (f.getClass() != MainFragment.class) {
Fragment fragment = null;
try {
fragment = (Fragment) MainFragment.class.newInstance();
} catch (Exception e) {
e.printStackTrace();
}
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.frame, fragment).commit(); // this is your framelayout
}else {
super.onBackPressed();
}
}
}
getVisibleFragment()函数
public Fragment getVisibleFragment() {
FragmentManager fragmentManager = NavigationActivity.this.getSupportFragmentManager();
List<Fragment> fragments = fragmentManager.getFragments();
if (fragments != null) {
for (Fragment fragment : fragments) {
if (fragment != null && fragment.isVisible())
return fragment;
}
}
return null;
}
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