Android知識總結
一、使用navigation角度上分析源碼
1、Fragment
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val btn = view.findViewById<Button>(R.id.btn)
btn.setOnClickListener { view ->
// 在這裏開始導航
Navigation.findNavController(view).navigate(R.id.action_page2)
}
}
2、 NavController.navigation
public void navigate(@IdRes int resId) {
navigate(resId, null);
}
public void navigate(@IdRes int resId, @Nullable Bundle args) {
navigate(resId, args, null);
}
public void navigate(@IdRes int resId, @Nullable Bundle args,
@Nullable NavOptions navOptions) {
navigate(resId, args, navOptions, null);
}
public void navigate(@IdRes int resId, @Nullable Bundle args, @Nullable NavOptions navOptions,
@Nullable Navigator.Extras navigatorExtras) {
// 目的 是在 Graph裏面去尋找 當前節點的Fragment 爲 目的地
NavDestination currentNode = mBackStack.isEmpty() // 先去看看棧有沒有
? mGraph
: mBackStack.getLast().getDestination(); // 如果棧沒有,就取最後一個
if (currentNode == null) {
throw new IllegalStateException("no current navigation node");
}
@IdRes int destId = resId;
// 獲取節點後,就要去獲取 action 導航動作,只有action才能通過resId 獲取下一個要導航的目標id
final NavAction navAction = currentNode.getAction(resId);
Bundle combinedArgs = null;
if (navAction != null) {
if (navOptions == null) {
navOptions = navAction.getNavOptions();
}
// 獲取下一個目的地的 id號信息等
destId = navAction.getDestinationId();
Bundle navActionArgs = navAction.getDefaultArguments();
if (navActionArgs != null) {
combinedArgs = new Bundle();
combinedArgs.putAll(navActionArgs);
}
}
if (args != null) {
if (combinedArgs == null) {
combinedArgs = new Bundle();
}
combinedArgs.putAll(args);
}
if (destId == 0 && navOptions != null && navOptions.getPopUpTo() != -1) {
popBackStack(navOptions.getPopUpTo(), navOptions.isPopUpToInclusive());
return;
}
if (destId == 0) {
throw new IllegalArgumentException("Destination id == 0 can only be used"
+ " in conjunction with a valid navOptions.popUpTo");
}
// 檢查健壯性
NavDestination node = findDestination(destId);
if (node == null) {
final String dest = NavDestination.getDisplayName(mContext, destId);
if (navAction != null) {
throw new IllegalArgumentException("Navigation destination " + dest
+ " referenced from action "
+ NavDestination.getDisplayName(mContext, resId)
+ " cannot be found from the current destination " + currentNode);
} else {
throw new IllegalArgumentException("Navigation action/destination " + dest
+ " cannot be found from the current destination " + currentNode);
}
}
// 這行代碼就是我們要關心的主線流程
navigate(node, combinedArgs, navOptions, navigatorExtras);
}
3、 NavController.navigation
private void navigate(@NonNull NavDestination node, @Nullable Bundle args,
@Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
boolean popped = false;
boolean launchSingleTop = false;
if (navOptions != null) {
if (navOptions.getPopUpTo() != -1) {
popped = popBackStackInternal(navOptions.getPopUpTo(),
navOptions.isPopUpToInclusive());
}
}
//這裏又回到了,最初開始的代碼
Navigator<NavDestination> navigator = mNavigatorProvider.getNavigator(
node.getNavigatorName());
Bundle finalArgs = node.addInDefaultArgs(args);
NavDestination newDest = navigator.navigate(node, finalArgs,
navOptions, navigatorExtras);
if (newDest != null) {
if (!(newDest instanceof FloatingWindow)) {
// We've successfully navigating to the new destination, which means
// we should pop any FloatingWindow destination off the back stack
// before updating the back stack with our new destination
//noinspection StatementWithEmptyBody
while (!mBackStack.isEmpty()
&& mBackStack.peekLast().getDestination() instanceof FloatingWindow
&& popBackStackInternal(
mBackStack.peekLast().getDestination().getId(), true)) {
// Keep popping
}
}
// When you navigate() to a NavGraph, we need to ensure that a new instance
// is always created vs reusing an existing copy of that destination
ArrayDeque<NavBackStackEntry> hierarchy = new ArrayDeque<>();
NavDestination destination = newDest;
if (node instanceof NavGraph) {
do {
NavGraph parent = destination.getParent();
if (parent != null) {
NavBackStackEntry entry = new NavBackStackEntry(mContext, parent,
finalArgs, mLifecycleOwner, mViewModel);
hierarchy.addFirst(entry);
// Pop any orphaned copy of that navigation graph off the back stack
if (!mBackStack.isEmpty()
&& mBackStack.getLast().getDestination() == parent) {
popBackStackInternal(parent.getId(), true);
}
}
destination = parent;
} while (destination != null && destination != node);
}
// Now collect the set of all intermediate NavGraphs that need to be put onto
// the back stack
destination = hierarchy.isEmpty()
? newDest
: hierarchy.getFirst().getDestination();
while (destination != null && findDestination(destination.getId()) == null) {
NavGraph parent = destination.getParent();
if (parent != null) {
NavBackStackEntry entry = new NavBackStackEntry(mContext, parent, finalArgs,
mLifecycleOwner, mViewModel);
hierarchy.addFirst(entry);
}
destination = parent;
}
NavDestination overlappingDestination = hierarchy.isEmpty()
? newDest
: hierarchy.getLast().getDestination();
// Pop any orphaned navigation graphs that don't connect to the new destinations
//noinspection StatementWithEmptyBody
while (!mBackStack.isEmpty()
&& mBackStack.getLast().getDestination() instanceof NavGraph
&& ((NavGraph) mBackStack.getLast().getDestination()).findNode(
overlappingDestination.getId(), false) == null
&& popBackStackInternal(mBackStack.getLast().getDestination().getId(), true)) {
// Keep popping
}
mBackStack.addAll(hierarchy);
// The mGraph should always be on the back stack after you navigate()
if (mBackStack.isEmpty() || mBackStack.getFirst().getDestination() != mGraph) {
NavBackStackEntry entry = new NavBackStackEntry(mContext, mGraph, finalArgs,
mLifecycleOwner, mViewModel);
mBackStack.addFirst(entry); // 留意一下,每次都會管理 進棧
}
// And finally, add the new destination with its default args
NavBackStackEntry newBackStackEntry = new NavBackStackEntry(mContext, newDest,
newDest.addInDefaultArgs(finalArgs), mLifecycleOwner, mViewModel);
mBackStack.add(newBackStackEntry);
} else if (navOptions != null && navOptions.shouldLaunchSingleTop()) {
launchSingleTop = true;
NavBackStackEntry singleTopBackStackEntry = mBackStack.peekLast();
if (singleTopBackStackEntry != null) {
singleTopBackStackEntry.replaceArguments(finalArgs);
}
}
updateOnBackPressedCallbackEnabled();
if (popped || newDest != null || launchSingleTop) {
dispatchOnDestinationChanged();
}
}