我在泡菜，不知道发生了什么。我的应用程序使用带有关闭窗口和主屏幕检查的OnBackPressed，总之“如果是主屏幕，否则，请使用退出菜单”
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else if (!viewIsAtHome) {
displayView(R.id.nav_large_monsters);
} else {
new AlertDialog.Builder(this)
.setMessage("Are you sure you want to exit?")
.setCancelable(false)
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
Home.this.finish();
}
})
.setNegativeButton("No", null)
.show();
}
}
我不希望发生的事情是，按回去会使我直接回到我的“大怪物”片段。我想让它跟进栈。
我在“大型怪物”页面上有大约30个按钮，可以带您进入怪物的信息，但是立即按回去会弹出“您确定要退出”菜单，而不是返回到大型怪物片段：
Large Monsters
Pressing Back button from a Monster fragment
显然，它并没有跟进栈。与任何其他屏幕相同，如果我执行其他任何片段，它将直接将我带回到Nav_Large_Monsters，而不是跟随后退堆栈。
我假设我的问题是这样的：
} else if (!viewIsAtHome) {
displayView(R.id.nav_large_monsters);
但是，如果我将其删除，则该应用程序将希望立即要求退出，而不是返回家园，仍然不追随Backstack。
如果我将onBackPressed返回其默认代码，它将遵循Backstack，但不会加载主片段并以空白片段开头。
尝试：
我试图删除onBackPressed中的“ else if（！viewIsAtHome）”部分，并在我的onNavigationItemSelected方法中实现了“默认”
default:
fragment = new Large_Monsters();
break;
这也行不通。不加载主片段。
以前我有一个showHome（）方法，此DID可以使用backStack和使用家庭片段，但是将Fragments更改为v4.support.app.Fragment之后，我不得不更改Home Activity的处理方式我的onNavigationItemSelected。它不喜欢我的showHome方法，并不断指出我使用的是旧的FragmentManager而不是v4.support.app.FragmentManager（此方法导致我的应用程序在更改为v4后立即崩溃）：
private void showHome() {
fragment = new Large_Monsters();
if (fragment != null) {
android.app.FragmentManager fragMgmt = getFragmentManager();
fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();
}
}
我还尝试添加一个关于弹出backStack的If语句，这似乎没有任何效果：
if (!fragment.getFragmentManager().popBackStackImmediate()) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
finishAfterTransition();
}
}
我还尝试添加一个If语句来检查Backstack是否> 0，但这也无济于事，尽管我删除了该字符串并不确定在哪里找到它。也许我没有正确地构建该字符串。
任何帮助将是巨大的！谢谢！
码：
Home.java（MainActivity，我在该项目上将其命名为Home）
public class Home extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
private Fragment fragment = null;
private FragmentManager fragmentManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DatabaseHelper myDbHelper = new DatabaseHelper(Home.this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
navigationView.setItemIconTintList(null);
// showHome();
displayView(R.id.nav_large_monsters);
}
private boolean viewIsAtHome;
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else if (!viewIsAtHome) {
displayView(R.id.nav_large_monsters);
} else {
new AlertDialog.Builder(this)
.setMessage("Are you sure you want to exit?")
.setCancelable(false)
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
Home.this.finish();
}
})
.setNegativeButton("No", null)
.show();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.search_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
return super.onOptionsItemSelected(item);
}
// private void showHome() {
// fragment = new Large_Monsters();
// if (fragment != null) {
// android.app.FragmentManager fragMgmt = getFragmentManager();
// fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();
// }
// }
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
displayView(item.getItemId());
return true;
}
public void displayView(int viewId) {
Fragment fragment = null;
String title = getString(R.string.app_name);
switch (viewId) {
case R.id.nav_large_monsters:
fragment = new Large_Monsters();
title = "Large Monsters";
viewIsAtHome = true;
break;
case R.id.nav_small_monsters:
fragment = new Small_Monsters();
title = "Small Monsters";
viewIsAtHome = false;
break;
case R.id.nav_weapons:
fragment = new Weapons();
title = "Weapons";
viewIsAtHome = false;
break;
case R.id.nav_armors:
fragment = new Armors_Low_High();
title = "Armor Sets";
viewIsAtHome = false;
break;
case R.id.nav_charms:
fragment = new Charms();
title = "Charms";
viewIsAtHome = false;
break;
case R.id.nav_items:
fragment = new Items();
title = "Items";
viewIsAtHome = false;
break;
case R.id.palico_armor:
fragment = new Palico_Armor();
title = "Palico Armor";
viewIsAtHome = false;
break;
case R.id.palico_gadgets:
fragment = new Palico_Gadgets();
title = "Palico Gadgets";
viewIsAtHome = false;
break;
case R.id.palico_weps:
fragment = new Palico_Weapons();
title = "Palico Weapons";
viewIsAtHome = false;
break;
case R.id.palico_helms:
fragment = new Palico_Helms();
title = "Palico Helmets";
viewIsAtHome = false;
break;
default:
fragment = new Large_Monsters();
break;
}
if (fragment != null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction()
.replace(R.id.content_frame, fragment, fragment.getTag())
.addToBackStack(null);
ft.commit();
}
// set the toolbar title
if (getSupportActionBar() != null) {
getSupportActionBar().setTitle(title);
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
}
}
最佳答案
如果要覆盖onBackPressed，则必须自己处理回溯。这是FragmentActivity的作用：
/**
* Take care of popping the fragment back stack or finishing the activity
* as appropriate.
*/
@Override
public void onBackPressed() {
FragmentManager fragmentManager = mFragments.getSupportFragmentManager();
final boolean isStateSaved = fragmentManager.isStateSaved();
if (isStateSaved && Build.VERSION.SDK_INT <= Build.VERSION_CODES.N_MR1) {
// Older versions will throw an exception from the framework
// FragmentManager.popBackStackImmediate(), so we'll just
// return here. The Activity is likely already on its way out
// since the fragmentManager has already been saved.
return;
}
if (isStateSaved || !fragmentManager.popBackStackImmediate()) {
super.onBackPressed();
}
}
如果跳过该步骤，则不会出现片段弹出行为。因此，只需更新您的
onBackPressed使其包含片段管理器的弹出窗口即可-如果成功，则可以提早返回，因为系统已根据需要执行了弹出片段的操作。@Override
public void onBackPressed() {
// Pressing back popped the back stack, nothing else to do
FragmentManager fragmentManager = getSupportFragmentManager();
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else if (!fragmentManager.isStateSaved() && fragmentManager.popBackStackImmediate()) {
return;
} else {
new AlertDialog.Builder(this)
.setMessage("Are you sure you want to exit?")
.setCancelable(false)
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
Home.this.finish();
}
})
.setNegativeButton("No", null)
.show();
}
}
更新
您还需要更新
displayView方法，因为现在它总是将某些内容压入堆栈。因此，您的“ home”片段实际上将是堆栈中的第一件事，并且会弹出并显示空白屏幕。因此，如果要显示“ home”片段，请不要在片段管理器上调用addToBackStack。此外，您不需要在按下时显式设置“ home”片段，因为弹出后退堆栈应该做正确的事情（请参见上面的更新示例）。
希望有帮助！
关于java - OnBackPressed不跟随后退；直接回家 fragment ，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/49968397/