快速创建一个Navigation项目 直接在Android studio中创建一个Navigation界面的activity 工具就帮我们创建好了
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在运行跑项目的时候发现- -切换了下fragment 上一个界面的fragment 已经被销毁了查了下资料发现这个其实不是bug而是特定这么设计的 翻了下源码 发现FragmentNavigator 中navigate方法是直接用Fragment的replace把fragment进行了替换
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既然知道为啥切换fragment 会被销毁的原因了 那么解决方案就出来了
把 replace 换成 show和hide 就行了
废话不多说 直接上代码 写一个类继承FragmentNavigator 重写 navigate方法
@Navigator.Name("fixFragment") //fix 5: 需要指定1个名字，源码里自带的名字有navigation、activity、fragment、dialog
public class FixFragmentNavigator extends FragmentNavigator {
private static final String TAG = "FixFragmentNavigator";
private Context mContext;
private FragmentManager mFragmentManager;
private int mContainerId;
public FixFragmentNavigator(@NonNull Context context, @NonNull FragmentManager manager, int containerId) {
super(context, manager, containerId);
mContext = context;
mFragmentManager = manager;
mContainerId = containerId;
}
@Nullable
@Override
public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args, @Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
if (mFragmentManager.isStateSaved()) {
Log.i(TAG, "Ignoring navigate() call: FragmentManager has already"
+ " saved its state");
return null;
}
String className = destination.getClassName();
if (className.charAt(0) == '.') {
className = mContext.getPackageName() + className;
}
//fix 1: 把类名作为tag，寻找已存在的Fragment
//（如果想只针对个别fragment进行保活复用，可以在tag上做些标记比如加个前缀）
Fragment frag = mFragmentManager.findFragmentByTag(className);
if (null == frag) {
//不存在，则创建
frag = instantiateFragment(mContext, mFragmentManager, className, args);
}
frag.setArguments(args);
final FragmentTransaction ft = mFragmentManager.beginTransaction();
int enterAnim = navOptions != null ? navOptions.getEnterAnim() : -1;
int exitAnim = navOptions != null ? navOptions.getExitAnim() : -1;
int popEnterAnim = navOptions != null ? navOptions.getPopEnterAnim() : -1;
int popExitAnim = navOptions != null ? navOptions.getPopExitAnim() : -1;
if (enterAnim != -1 || exitAnim != -1 || popEnterAnim != -1 || popExitAnim != -1) {
enterAnim = enterAnim != -1 ? enterAnim : 0;
exitAnim = exitAnim != -1 ? exitAnim : 0;
popEnterAnim = popEnterAnim != -1 ? popEnterAnim : 0;
popExitAnim = popExitAnim != -1 ? popExitAnim : 0;
ft.setCustomAnimations(enterAnim, exitAnim, popEnterAnim, popExitAnim);
}
// ft.replace(mContainerId, frag);
//fix 2: replace换成show和hide
List<Fragment> fragments = mFragmentManager.getFragments();
for (Fragment fragment : fragments) {
ft.hide(fragment);
}
if (!frag.isAdded()) {
ft.add(mContainerId, frag, className);
}
ft.show(frag);
ft.setPrimaryNavigationFragment(frag);
final @IdRes int destId = destination.getId();
//fix 3: mBackStack是私有的，而且没有暴露出来，只能反射获取
ArrayDeque<Integer> mBackStack;
try {
Field field = FragmentNavigator.class.getDeclaredField("mBackStack");
field.setAccessible(true);
mBackStack = (ArrayDeque<Integer>) field.get(this);
} catch (Exception e) {
e.printStackTrace();
return null;
}
final boolean initialNavigation = mBackStack.isEmpty();
final boolean isSingleTopReplacement = navOptions != null && !initialNavigation
&& navOptions.shouldLaunchSingleTop()
&& mBackStack.peekLast() == destId;
boolean isAdded;
if (initialNavigation) {
isAdded = true;
} else if (isSingleTopReplacement) {
if (mBackStack.size() > 1) {
mFragmentManager.popBackStack(
generateBackStackName(mBackStack.size(), mBackStack.peekLast()),
FragmentManager.POP_BACK_STACK_INCLUSIVE);
ft.addToBackStack(generateBackStackName(mBackStack.size(), destId));
}
isAdded = false;
} else {
ft.addToBackStack(generateBackStackName(mBackStack.size() + 1, destId));
isAdded = true;
}
if (navigatorExtras instanceof Extras) {
Extras extras = (Extras) navigatorExtras;
for (Map.Entry<View, String> sharedElement : extras.getSharedElements().entrySet()) {
ft.addSharedElement(sharedElement.getKey(), sharedElement.getValue());
}
}
ft.setReorderingAllowed(true);
ft.commit();
if (isAdded) {
mBackStack.add(destId);
return destination;
} else {
return null;
}
}
//fix 4: 从父类那边copy过来即可
@NonNull
private String generateBackStackName(int backStackIndex, int destId) {
return backStackIndex + "-" + destId;
}
}
下面是activity的代码
public class MainActivity extends AppCompatActivity {
private TextView text;
private TestViewModel viewModel;
// @Override
// protected void onCreate(Bundle savedInstanceState) {
// super.onCreate(savedInstanceState);
// setContentView(R.layout.activity_main5);
// text = findViewById(R.id.text);
// BottomNavigationView navView = findViewById(R.id.nav_view);
// // Passing each menu ID as a set of Ids because each
// // menu should be considered as top level destinations.
// AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
// R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications)
// .build();
// NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
// NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
// NavigationUI.setupWithNavController(navView, navController);
// viewModel = new ViewModelProvider(this).get(TestViewModel.class);
// viewModel.name.observe(this, new Observer<String>() {
// @Override
// public void onChanged(String s) {
// text.setText(s);
// }
// });
// }
BottomNavigationView navView;
NavController navController;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main5);
text = findViewById(R.id.text);
navView = findViewById(R.id.nav_view);
viewModel = new ViewModelProvider(this).get(TestViewModel.class);
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
//获取导航控制器
navController = NavHostFragment.findNavController(fragment);
//创建自定义的Fragment导航器
FixFragmentNavigator fragmentNavigator =
new FixFragmentNavigator(this, fragment.getChildFragmentManager(), fragment.getId());
//获取导航器提供者
NavigatorProvider provider = navController.getNavigatorProvider();
//把自定义的Fragment导航器添加进去
provider.addNavigator(fragmentNavigator);
//手动创建导航图
NavGraph navGraph = initNavGraph(provider, fragmentNavigator);
//设置导航图
navController.setGraph(navGraph);
//底部导航设置点击事件
navView.setOnNavigationItemSelectedListener(item -> {
navController.navigate(item.getItemId());
return true;
});
viewModel.name.observe(this, new Observer<String>() {
@Override
public void onChanged(String s) {
text.setText(s);
}
});
}
//手动创建导航图，把3个目的地添加进来
private NavGraph initNavGraph(NavigatorProvider provider, FixFragmentNavigator fragmentNavigator) {
NavGraph navGraph = new NavGraph(new NavGraphNavigator(provider));
//用自定义的导航器来创建目的地
FragmentNavigator.Destination destination1 = fragmentNavigator.createDestination();
destination1.setId(R.id.navigation_home);
destination1.setClassName(HomeFragment.class.getCanonicalName());
destination1.setLabel(getResources().getString(R.string.title_home));
navGraph.addDestination(destination1);
FragmentNavigator.Destination destination2 = fragmentNavigator.createDestination();
destination2.setId(R.id.navigation_dashboard);
destination2.setClassName(DashboardFragment.class.getCanonicalName());
destination2.setLabel(getResources().getString(R.string.title_dashboard));
navGraph.addDestination(destination2);
FragmentNavigator.Destination destination3 = fragmentNavigator.createDestination();
destination3.setId(R.id.navigation_notifications);
destination3.setClassName(NotificationsFragment.class.getCanonicalName());
destination3.setLabel(getResources().getString(R.string.title_notifications));
navGraph.addDestination(destination3);
navGraph.setStartDestination(R.id.navigation_home);
return navGraph;
}
/**
* 重写返回键事件
* fix: ComponentActivity.onBackPressed -> ... -> NavController.popBackStack()
* 自定义导航器后，会引起NavController管理的回退栈出问题
*/
@Override
public void onBackPressed() {
int currentId = navController.getCurrentDestination().getId();
int startId = navController.getGraph().getStartDestination();
//如果当前目的地不是HomeFragment，则先回到HomeFragment
if (currentId != startId) {
navView.setSelectedItemId(startId);
} else {
finish();
}
}
}
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