这一篇我们将使用
NavigationApp
Navigation官网地址
快速入门
导航组件由以下三个关键部分组成：
导航图：在一个集中位置包含所有导航相关信息的 XML 资源。这包括应用内所有单个内容区域（称为目标）以及用户可以通过应用获取的可能路径。 NavHost：显示导航图中目标的空白容器。导航组件包含一个默认 NavHost 实现 (NavHostFragment)，可显示 Fragment 目标。 NavController：在 NavHost 中管理应用导航的对象。当用户在整个应用中移动时，NavController 会安排 NavHost 中目标内容的交换。Navigation这里我们直接使用AS自带的模板创建一个
Activity
看下它的布局，很简单就是两部分，底部的
BottomNavigationViewfragmentfragmentNavHostFragmentFragmentpublic class NavHostFragment extends Fragment implements NavHost {
......
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final Context context = getContext();
//实例化NavController，它才是真正处理导航的，并且把FragmentNavigator实例化添加到SimpleNavigatorProvider
mNavController = new NavController(context);
mNavController.getNavigatorProvider().addNavigator(createFragmentNavigator());
}
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
FrameLayout frameLayout = new FrameLayout(inflater.getContext());
frameLayout.setId(getId());
return frameLayout;
}
//onViewCreated传入当前的根布局以及NavController实例，并且给根布局设置一个tag，所以在每次findNavController的时候都会通过这个tag取唯一的实例，如果取不到会循环从父布局在去找。
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if (!(view instanceof ViewGroup)) {
throw new IllegalStateException("created host view " + view + " is not a ViewGroup");
}
View rootView = view.getParent() != null ? (View) view.getParent() : view;
Navigation.setViewNavController(rootView, mNavController);
}
public static void setViewNavController(@NonNull View view,
@Nullable NavController controller) {
view.setTag(R.id.nav_controller_view_tag, controller);
}
......
}
通过上面源码我们知道
NavHostFragmentNavControllernavigate
public void navigate(int resId, Bundle args, NavOptions navOptions) {
//回退栈为null返回NavGraph
//不为null返回回退栈中的最后一项
NavDestination currentNode = mBackStack.isEmpty() ? mGraph : mBackStack.peekLast();
if (currentNode == null) {
throw new IllegalStateException("no current navigation node");
}
int destId = resId;
//获取resId对应的NavAction
final NavAction navAction = currentNode.getAction(resId);
if (navAction != null) {
if (navOptions == null) {
navOptions = navAction.getNavOptions();
}
//通过NavAction获取目的地id
destId = navAction.getDestinationId();
}
//若destId为0而navOptions又不为null则弹出到该navOptions的指定的页面
if (destId == 0 && navOptions != null && navOptions.getPopUpTo() != 0) {
popBackStack(navOptions.getPopUpTo(), navOptions.isPopUpToInclusive());
return;
}
//为0报错
if (destId == 0) {
throw new IllegalArgumentException("Destination id == 0 can only be used" + " in conjunction with navOptions.popUpTo != 0");
}
//找到准备前往的目的地
NavDestination node = findDestination(destId);
if (node == null) {
final String dest = NavDestination.getDisplayName(mContext, destId);
throw new IllegalArgumentException("navigation destination " + dest
+ (navAction != null
? " referenced from action " + NavDestination.getDisplayName(mContext, resId)
: "")
+ " is unknown to this NavController");
}
if (navOptions != null) {
//是否清除回退栈
if (navOptions.shouldClearTask()) {
popBackStack(0, true);
mBackStack.clear();
} else if (navOptions.getPopUpTo() != 0) {
//导航之前弹出栈到指定栈
// 是否将该页面也弹出
popBackStack(navOptions.getPopUpTo(), navOptions.isPopUpToInclusive());
}
}
//进行导航
node.navigate(args, navOptions);
}
这里我们还需要介绍两个类
NavDestinationNavGraphNavGraphNavDestinationNavDestination
接下来说说我们
activity_mainBottomNavigationView
用它的话你需要添加依赖
implementation 'com.google.android.material:material:1.1.0'
我们需要给他配置一个
menu
我们回到
MainActivitypublic class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
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);
}
}
主要是在
NavigationUI.setupWithNavController(navView, navController); public static void setupWithNavController(
@NonNull final BottomNavigationView bottomNavigationView,
@NonNull final NavController navController) {
bottomNavigationView.setOnNavigationItemSelectedListener(
new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
return onNavDestinationSelected(item, navController);
}
});
final WeakReference weakReference =
new WeakReference(bottomNavigationView);
navController.addOnDestinationChangedListener(
new NavController.OnDestinationChangedListener() {
@Override
public void onDestinationChanged(@NonNull NavController controller,
@NonNull NavDestination destination, @Nullable Bundle arguments) {
BottomNavigationView view = weakReference.get();
if (view == null) {
navController.removeOnDestinationChangedListener(this);
return;
}
Menu menu = view.getMenu();
for (int h = 0, size = menu.size(); h < size; h++) {
MenuItem item = menu.getItem(h);
if (matchDestination(destination, item.getItemId())) {
item.setChecked(true);
}
}
}
});
}
这里分别监听了
BottomNavigationViewNavControllerNavControllerBottomNavigationView public static boolean onNavDestinationSelected(@NonNull MenuItem item,
@NonNull NavController navController) {
NavOptions.Builder builder = new NavOptions.Builder()
.setLaunchSingleTop(true)
.setEnterAnim(R.anim.nav_default_enter_anim)
.setExitAnim(R.anim.nav_default_exit_anim)
.setPopEnterAnim(R.anim.nav_default_pop_enter_anim)
.setPopExitAnim(R.anim.nav_default_pop_exit_anim);
if ((item.getOrder() & Menu.CATEGORY_SECONDARY) == 0) {
builder.setPopUpTo(findStartDestination(navController.getGraph()).getId(), false);
}
NavOptions options = builder.build();
try {
//TODO provide proper API instead of using Exceptions as Control-Flow.
navController.navigate(item.getItemId(), null, options);
return true;
} catch (IllegalArgumentException e) {
return false;
}
}
最终还是会调用
navController.navigate(item.getItemId(), null, options);OK,我们运行下看看效果
这里跟我们要实现的效果很像，但是还有些问题，一个是我们想动态添加底部，不在xml写死；我们在点击底部item的时候不要这个放大缩小动画；切换的时候
Fragmentreplace作者：Greathfs
