Navigation
Navigation是Jetpack中一种导航架构,大多是用在管理Fragment上面,不过也可以用来管理Activity,这一节主要是Navigation的入门,写了一个小Demo。
1 首先 是需要在app下gradle 添加依赖:
implementation 'androidx.navigation:navigation-fragment:2.2.2'
implementation 'androidx.navigation:navigation-ui:2.2.2'
2 布局:
activity_navigation.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/nav_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="@menu/bottom_nav_menu"
/>
<fragment
android:id="@+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:defaultNavHost="false"
app:layout_constraintBottom_toTopOf="@id/nav_view"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent"
/>
</androidx.constraintlayout.widget.ConstraintLayout>
说明:这里的android:name="androidx.navigation.fragment.NavHostFragment"是为了使当前的acitivity能够可以加载并使用navigation管理相关的fragment,除了在layout布局中创建外,也可以在activity中添加创建。
3 创建navigation文件
在res目录下创建一个navigation文件夹,新建对应的navigation布局,mobile_navigation如下:
<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/mobile_navigation"
app:startDestination="@+id/navigation_home"
>
<fragment
android:id="@+id/navigation_home"
android:name="com.sky.jetpacklearn.navigation.HomeFragment"
android:label="@string/title_home"
tools:layout="@layout/fragment_home"
/>
<fragment
android:id="@+id/navigation_dashboard"
android:name="com.sky.jetpacklearn.navigation.DashboardFragment"
android:label="@string/title_dashboard"
tools:layout="@layout/fragment_dashboard"
/>
<fragment
android:id="@+id/navigation_notification"
android:name="com.sky.jetpacklearn.navigation.NotificationsFragment"
android:label="@string/title_notifications"
tools:layout="@layout/fragment_notifications"
/>
</navigation>
HomeFragment.java(其他两个Fragment类似)
public class HomeFragment extends BaseFragment {
private HomeViewModel homeViewModel;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
homeViewModel = ViewModelProviders.of(this).get(HomeViewModel.class);
View root = inflater.inflate(R.layout.fragment_home, container, false);
final TextView textView = root.findViewById(R.id.text_home);
homeViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
@Override
public void onChanged(String s) {
textView.setText(s);
}
});
return root;
}
}
fragment_home.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".navigation.HomeFragment">
<TextView
android:id="@+id/text_home"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:textAlignment="center"
android:textSize="20sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:ignore="RtlCompat" />
</androidx.constraintlayout.widget.ConstraintLayout>
import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;
public class HomeViewModel extends ViewModel {
private MutableLiveData<String> mText;
public HomeViewModel() {
mText = new MutableLiveData<>();
mText.setValue("This is home fragment");
}
public LiveData<String> getText() {
return mText;
}
}
注:需在gradle添加依赖:
android {
...
buildFeatures{
dataBinding = true
}
...
}
def lifecycle_version = "2.2.0"
implementation "androidx.lifecycle:lifecycle-common-java8:$lifecycle_version"
implementation "android.arch.lifecycle:extensions:$lifecycle_version"
FixFragmentNavigator.java
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import androidx.annotation.IdRes;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;
import androidx.navigation.NavDestination;
import androidx.navigation.NavOptions;
import androidx.navigation.Navigator;
import androidx.navigation.fragment.FragmentNavigator;
import java.lang.reflect.Field;
import java.util.ArrayDeque;
import java.util.List;
import java.util.Map;
/**
* 支持fragment复用的导航器,搜"//fix"可快速定位到修复点
*/
@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;
}
}
NavigationActivity.java
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.navigation.NavController;
import androidx.navigation.NavGraph;
import androidx.navigation.NavGraphNavigator;
import androidx.navigation.NavigatorProvider;
import androidx.navigation.fragment.FragmentNavigator;
import androidx.navigation.fragment.NavHostFragment;
import android.os.Bundle;
import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.sky.jetpacklearn.R;
public class NavigationActivity extends AppCompatActivity {
BottomNavigationView navView;
NavController navController;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_navigation);
navView = findViewById(R.id.nav_view);
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
navController = NavHostFragment.findNavController(fragment);
FixFragmentNavigator fragmentNavigator = new FixFragmentNavigator(this,
fragment.getChildFragmentManager(),fragment.getId());
NavigatorProvider provider = navController.getNavigatorProvider();
provider.addNavigator(fragmentNavigator);
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;
});
}
private NavGraph initNavGraph(NavigatorProvider provider,FixFragmentNavigator fragmentNavigator) {
NavGraph navGraph = new NavGraph(new NavGraphNavigator(provider));
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;
}
@Override
public void onBackPressed() {
int currentId = navController.getCurrentDestination().getId();
int startId = navController.getGraph().getStartDestination();
if(currentId != startId) {
navView.setSelectedItemId(startId);
} else {
finish();
}
}
}
以上就是Navigation的主要代码。