Android Jetpack之Navigation源碼分析
Android Navigation簡介
關於Fragment的基礎篇:Fragment基礎篇
官方指導地址:官方指地址
Github demo 地址:demo
使用Navigation可以管理APP頁面跳轉。Navigation不部分情況下作用於Fragment中,使用Navigation切換Fragment可以使代碼簡潔,直觀。Navigation導航組件還支持:Fragment、Activity、導航圖和子圖、自定義目標等。
Navigation的使用
基礎使用
- 添加項目組件依賴
def nav_dep = "2.0.0"
implementation "androidx.navigation:navigation-fragment:$nav_dep"
implementation "androidx.navigation:navigation-ui:$nav_dep"
- 導航文件XML
在module下的res目錄下,新建navigation文件夾,然後在navigation文件夾下新建一個navigation的xml文件:navigation_jetpack.xml
<?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"
app:startDestination="@id/first_fragment">
<fragment
android:id="@+id/first_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.FirstNavigationFragment"
android:label="first_fragment"
tools:layout="@layout/fragment_first_navigation">
<action
android:id="@+id/action_to_second_fragment"
app:destination="@id/second_fragment" />
</fragment>
<fragment
android:id="@+id/second_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.SecondNavigationFragment"
android:label="second_fragment"
tools:layout="@layout/fragment_second_navigation">
<action
android:id="@+id/action_popup_to_first_fragment"
app:popUpTo="@id/first_fragment" />
<action
android:id="@+id/action_to_third_fragment"
app:destination="@id/third_fragment" />
<argument
android:name="title" app:argType="string" android:defaultValue="jetpack navigation"
/>
</fragment>
<fragment
android:id="@+id/third_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.ThirdNavigationFragment"
android:label="third_navigation"
tools:layout="@layout/fragment_third_navigation" >
<action android:id="@+id/action_popup_to_first_fragment_from_third"
app:popUpTo="@id/first_fragment"/>
</fragment>
</navigation>
字段解析:
(1)navigation根節點 startDestination 表示第一個顯示的fragment。即FirstNavigationFragment
(2)fragment 節點中name屬性表示所屬的fragment類
(3)fragment 節點中action節點destination屬性用於指定下一個目標fragment
(4)fragment 節點中argument 用於傳遞數據。表示的是傳遞到當前Fragment的數據,Key爲name屬性,默認數據是android:defaultValue,數據類型是argType。
3. 創建Fragment
以ThirdNavigationFragment爲例。onCreateView返回佈局View。onViewCreated設置點擊時間,執行相應的action,來完成Fragment的跳轉。在頁面跳歡時,會執行onDestroyView方法,從新回到該Fragment,會執行方法onCreateView方法。
class ThirdNavigationFragment : Fragment(){
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
return LayoutInflater.from(this.activity).inflate(R.layout.fragment_third_navigation,container,false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
btn_third_fragment.setOnClickListener{
Navigation.findNavController(it).navigate(R.id.action_popup_to_first_fragment_from_third)
}
}
}
- 創建Activity
4.1 activity佈局文件。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<!--xml實現-->
<fragment
android:id="@+id/fragment_navigation"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:name="androidx.navigation.fragment.NavHostFragment"
app:defaultNavHost="false"
app:navGraph="@navigation/navigation_jetpack"/>
<!--代碼實現-->
<FrameLayout
android:id="@+id/ll_fragment_navigation"
android:layout_width="match_parent"
android:layout_height="match_parent"
></FrameLayout>
</LinearLayout>
佈局解析:
(1)xml實現和代碼實現在使用時,請務必註解其中一個。
(2)如果使用xml實現,fragment務必設置id。navGraph 用來表示上面的導航意圖文件 navigation_jetpack.xml
(3)name 必須指定爲以下值,這是切換fragment的容器
android:name=“androidx.navigation.fragment.NavHostFragment”
(4)defaultNavHost 表示是否攔截返回鍵,默認爲false。
4.2 Activity中使用
如果使用的是代碼實現的佈局文件,在Activity中使用如下代碼:
(1)初始化NavHostFragment。
(2)將NavHostFragment綁定到佈局文件的FrameLayout中。
class NavigationActivity : AppCompatActivity(){
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_navigation)
val finalHost = NavHostFragment.create(R.navigation.navigation_jetpack)
supportFragmentManager.beginTransaction()
.replace(R.id.ll_fragment_navigation, finalHost)
.setPrimaryNavigationFragment(finalHost)
.commit()
}
}
- 切換fragment
切換Fragment主要有一下兩種方式:
(1)方式1:
Navigation.findNavController(it).navigate(R.id.action_to_second_fragment)
(2)方式2:
NavHostFragment.findNavController(this).navigate(R.id.action_to_second_fragment,null)
這兩種實現方式其實都返回了一個 NavController 類,然後再通過調用navigate方法控制頁面導航,也就是說通過NavController 我們可以控制所有的Fragment導航行爲。
7. 數據傳遞
在navigation導航文件中可以通過設置argument標籤,來設置fragment所接收的參數類型和默認值。
<argument
android:name="title" app:argType="string" android:defaultValue="jetpack navigation"
/>
或者在代碼中使用傳統方式:
val bundle = Bundle()
bundle.putString("name","Blank")
bundle.putInt("number",10)
NavHostFragment.findNavController(this).navigate(R.id.action_to_second_fragment,bundle)
在代碼中,使用navigate() 方法並將Bundle並將其傳遞到目標。接受方Fragment中,使用getArguments()方法檢索包並使用其內容。
8. 嵌套導航圖
可以將目的地分組爲導航圖中的子圖,子圖也被稱爲“ 嵌套圖 ”,包含圖稱爲“ 根圖“。如下我們建立子圖:third_navigation。
<?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"
app:startDestination="@id/first_fragment">
<fragment
android:id="@+id/first_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.FirstNavigationFragment"
android:label="first_fragment"
tools:layout="@layout/fragment_first_navigation">
<action
android:id="@+id/action_to_second_fragment"
app:destination="@id/second_fragment" />
</fragment>
<fragment
android:id="@+id/second_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.SecondNavigationFragment"
android:label="second_fragment"
tools:layout="@layout/fragment_second_navigation">
<action
android:id="@+id/action_popup_to_first_fragment"
app:popUpTo="@id/first_fragment" />
<action
android:id="@+id/action_to_third_fragment"
app:destination="@id/third_navigation" />
<argument
android:name="title" app:argType="string" android:defaultValue="jetpack navigation"
/>
</fragment>
<navigation
android:id="@+id/third_navigation"
app:startDestination="@id/third_fragment">
<fragment
android:id="@+id/third_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.ThirdNavigationFragment"
android:label="third_navigation"
tools:layout="@layout/fragment_third_navigation" >
<action android:id="@+id/action_popup_to_first_fragment_from_third"
app:popUpTo="@id/first_fragment"/>
</fragment>
</navigation>
</navigation>
- include引用其他圖形
使用include引用其他圖形
比如我們建立視圖:navigation_nested.xml 佈局文件如下:
<?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/navigation_nested"
app:startDestination="@id/third_fragment">
<fragment
android:id="@+id/third_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.ThirdNavigationFragment"
android:label="third_navigation"
tools:layout="@layout/fragment_third_navigation" >
<action android:id="@+id/action_popup_to_first_fragment_from_third"
app:popUpTo="@id/first_fragment"/>
</fragment>
</navigation>
在navigation_jetpack中include navigation_nested。
<?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"
app:startDestination="@id/first_fragment">
<fragment
android:id="@+id/first_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.FirstNavigationFragment"
android:label="first_fragment"
tools:layout="@layout/fragment_first_navigation">
<action
android:id="@+id/action_to_second_fragment"
app:destination="@id/second_fragment" />
</fragment>
<fragment
android:id="@+id/second_fragment"
android:name="com.jandroid.module_common.jetpack.navigation.SecondNavigationFragment"
android:label="second_fragment"
tools:layout="@layout/fragment_second_navigation">
<action
android:id="@+id/action_popup_to_first_fragment"
app:popUpTo="@id/first_fragment" />
<action
android:id="@+id/action_to_third_fragment"
app:destination="@id/navigation_nested" />
<argument
android:name="title" app:argType="string" android:defaultValue="jetpack navigation"
/>
</fragment>
<include app:graph="@navigation/navigation_nested"/>
</navigation>
- 其他用法
Navigation的其他用法可以參考下面Blog,包含Deep Link等。
https://cloud.tencent.com/developer/article/1446342
https://blog.csdn.net/lyhhj/article/details/93757755
https://cloud.tencent.com/developer/article/1452921
源碼分析
3.1 構建NavController
通過上面的Navigation使用,我們知道NavHostFragment作爲一個容器,所有的導航操作都是NavHostFragment中進行,在NavHostFragment中又委託給了NavController類。所以我們下面主要看看NavController類是如何被創建出來的,以及在創建過程中NavHostFragment類都做那些初始化工作。NavHostFragment的初始化主要有兩種實現方式,1:配置XML文件。2:代碼實現。下面我們以代碼實現NavHostFragment.create爲入口來分析,NavHostFragment類。
val finalHost = NavHostFragment.create(R.navigation.navigation_jetpack)
supportFragmentManager.beginTransaction()
.replace(R.id.ll_fragment_navigation, finalHost)
.setPrimaryNavigationFragment(finalHost)
.commit()
- NavHostFragment.create方法
(1)初始化Bundle,並且將graphResId,startDestinationArgs存儲在Bundle中。
(2)返回NavHostFragment實例。
public static NavHostFragment create(@NavigationRes int graphResId,
@Nullable Bundle startDestinationArgs) {
Bundle b = null;
if (graphResId != 0) {
b = new Bundle();
b.putInt(KEY_GRAPH_ID, graphResId);
}
if (startDestinationArgs != null) {
if (b == null) {
b = new Bundle();
}
b.putBundle(KEY_START_DESTINATION_ARGS, startDestinationArgs);
}
final NavHostFragment result = new NavHostFragment();
if (b != null) {
result.setArguments(b);
}
return result;
}
- NavHostFragment.onInflate方法
當Fragment以XML的方式靜態加載時,最先會調用onInflate的方法(調用時機:Fragment所關聯的Activity在執行setContentView時)。
(1)主要是解析佈局文件的兩個屬性。defaultNavHost和navGraph,並且初始化全局變量
(1)defaltNavHost爲true時,NavHostFragment將會通過FragmentManager 切換到回退棧頂部,並且可以攔截返回鍵事件(back事件)。
public void onInflate(@NonNull Context context, @NonNull AttributeSet attrs,
@Nullable Bundle savedInstanceState) {
super.onInflate(context, attrs, savedInstanceState);
final TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.NavHostFragment);
final int graphId = a.getResourceId(R.styleable.NavHostFragment_navGraph, 0);
final boolean defaultHost = a.getBoolean(R.styleable.NavHostFragment_defaultNavHost, false);
if (graphId != 0) {
mGraphId = graphId;
}
if (defaultHost) {
mDefaultNavHost = true;
}
a.recycle();
}
- NavHostFragment.onCreate方法。無論是XML實現還是代碼實現,都會執行Fragment的onCreate方法,可謂是殊途同歸。NavController在這裏被創建,並且NavHostFragment中有一個NavController對象。
(1)初始化NavController,NavController爲導航的控制類,核心類。
(2)在SimpleNavigatorProvider中以鍵值對保存FragmentNavigator類。該類之後會做介紹。
(3)savedInstanceState不爲空時候,恢復controller的狀態
(4)將graph設置給navController,構建NavGraph。下面會單獨分析該模塊。
(5)當defaltNavHost爲true,將會被設置爲主導航fragment。可以攔截返回鍵事件(back事件)。
(6)通過addNavigator添加FragmentNavigator,下面會分析到。
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final Context context = requireContext();
mNavController = new NavController(context);
mNavController.getNavigatorProvider().addNavigator(createFragmentNavigator());
Bundle navState = null;
if (savedInstanceState != null) {
navState = savedInstanceState.getBundle(KEY_NAV_CONTROLLER_STATE);
if (savedInstanceState.getBoolean(KEY_DEFAULT_NAV_HOST, false)) {
mDefaultNavHost = true;
requireFragmentManager().beginTransaction()
.setPrimaryNavigationFragment(this)
.commit();
}
}
if (navState != null) {
// Navigation controller state overrides arguments
mNavController.restoreState(navState);
}
if (mGraphId != 0) {
// Set from onInflate()
mNavController.setGraph(mGraphId);
} else {
// See if it was set by NavHostFragment.create()
final Bundle args = getArguments();
final int graphId = args != null ? args.getInt(KEY_GRAPH_ID) : 0;
final Bundle startDestinationArgs = args != null
? args.getBundle(KEY_START_DESTINATION_ARGS)
: null;
if (graphId != 0) {
mNavController.setGraph(graphId, startDestinationArgs);
}
}
}
- NavController.onCreateView方法
該NavHostFragment的視圖就只有一個FrameLayout佈局, 在NavHostFragment的創建時,爲它創建一個FrameLayout作爲導航界面的載體。
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
FrameLayout frameLayout = new FrameLayout(inflater.getContext());
// When added via XML, this has no effect (since this FrameLayout is given the ID
// automatically), but this ensures that the View exists as part of this Fragment's View
// hierarchy in cases where the NavHostFragment is added programmatically as is required
// for child fragment transactions
frameLayout.setId(getId());
return frameLayout;
}
- NavController.onViewCreated
(1)當通過XML添加時,父View是null,我們的view就是NavHostFragment的根。
(2)但是當以代碼方式添加時,需要在父級上設置NavController。
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");
}
// When added via XML, the parent is null and our view is the root of the NavHostFragment
// but when added programmatically, we need to set the NavController on the parent - i.e.,
// the View that has the ID matching this NavHostFragment.
View rootView = view.getParent() != null ? (View) view.getParent() : view;
Navigation.setViewNavController(rootView, mNavController);
}
- Navigation.setViewNavController方法。
主要是將NavController對象設置爲rootView的tag。方便以後遞歸遍歷到NavController對象,確保NavController對象的唯一。
public static void setViewNavController(@NonNull View view,
@Nullable NavController controller) {
view.setTag(R.id.nav_controller_view_tag, controller);
}
至此整個NavController對象和NavHostFragment的關係我們已經梳理明白了。下面來看看
NavController是如何參與到導航事件的。
3.2 獲取NavController
要想NavController參與到導航事件,必須獲取到該對象纔可以。在Fragment 中控制導航的時候,上面介紹了兩種實現方式。
(1)Navigation.findNavController(it).navigate(R.id.action_page)
(2)NavHostFragment.findNavController(this).navigate(R.id.action)
其實無論是通過findNavController或者是findNavController返回的都是NavController對象。
在構建NavController對象的時候,我們使用到了Navigation類,下面就從該類分析。findNavController方法形參是個View對象,所以是通過view就去查找就NavController,還記得上面用到的viewRoot嗎?。
- findNavController方法
該方法沒什麼實質性的代碼,只要是調用了findViewNavController方法。
public static NavController findNavController(@NonNull View view) {
NavController navController = findViewNavController(view);
if (navController == null) {
throw new IllegalStateException("View " + view + " does not have a NavController set");
}
return navController;
}
- findViewNavController方法
通過view遞歸循環查找NavController。內部調用了getViewNavController方法。
private static NavController findViewNavController(@NonNull View view) {
while (view != null) {
NavController controller = getViewNavController(view);
if (controller != null) {
return controller;
}
ViewParent parent = view.getParent();
view = parent instanceof View ? (View) parent : null;
}
return null;
}
- getViewNavController方法
通過獲取view的Tag,獲取NavController對象,這裏的tag ID和setViewNavController都是nav_controller_view_tag。
private static NavController getViewNavController(@NonNull View view) {
Object tag = view.getTag(R.id.nav_controller_view_tag);
NavController controller = null;
if (tag instanceof WeakReference) {
controller = ((WeakReference<NavController>) tag).get();
} else if (tag instanceof NavController) {
controller = (NavController) tag;
}
return controller;
}
至此NavController的獲取過程已經分析完畢。
4 真正的導航實現
在實現導航的時候,我們需要根據navigation配置文件生成NavGraph類,然後在根據每個不同的action id,找到對應的NavDestination就可以實現頁面導航跳轉了。
4.1 構建NavGraph
- SimpleNavigatorProvider類
在構建NavController的時候,在onCreate方法中調用瞭如下代碼。
mNavController = new NavController(context);
mNavController.getNavigatorProvider().addNavigator(createFragmentNavigator());
(1)其中mNavigatorProvider是NavController中的全局變量,內部通過HashMap鍵值對的形式保存Navigator類。
private final NavigatorProvider mNavigatorProvider = new NavigatorProvider() {
@Nullable
@Override
public Navigator<? extends NavDestination> addNavigator(@NonNull String name,
@NonNull Navigator<? extends NavDestination> navigator) {
Navigator<? extends NavDestination> previousNavigator =
super.addNavigator(name, navigator);
if (previousNavigator != navigator) {
if (previousNavigator != null) {
previousNavigator.removeOnNavigatorBackPressListener(mOnBackPressListener);
}
navigator.addOnNavigatorBackPressListener(mOnBackPressListener);
}
return previousNavigator;
}
};
(2)createFragmentNavigator方法,構建了FragmentNavigator對象,其中抽象類Navigator還有個重要的實現類ActivityNavigator和NavGraphNavigator。這個兩個類的對象在NavController的構造方法中被添加。。
public class FragmentNavigator extends Navigator<FragmentNavigator.Destination>
(3)其中Navigator類的作用是:能夠實例化對應的NavDestination,並且能夠實現導航功能,擁有自己的回退棧。
2. 構建NavGraph
在構建NavController的時候,我們還調用了NavController.setGraph(graphId)方法,該方法主要是構建NavGraph。
(1)調用getNavInflater方法創建NavInflater對象,用於解析navigation xml文件
public void setGraph(@NavigationRes int graphResId, @Nullable Bundle startDestinationArgs) {
setGraph(getNavInflater().inflate(graphResId), startDestinationArgs);
}
(2) NavInflater.inflate方法
根據傳入的XML資源id構建NavGraph,NavGraph組成Fragment路由的導航地圖,而NavDestination代表了導航的每一個目的地。在解析完NavDestination後,需要要求NavDestination爲NavGraph,即NavGraph是NavDestination的子類。而且在NavGraph內部存儲了NavDestination信息。
public NavGraph inflate(@NavigationRes int graphResId) {
Resources res = mContext.getResources();
//拿到XML的解析器
XmlResourceParser parser = res.getXml(graphResId);
final AttributeSet attrs = Xml.asAttributeSet(parser);
try {
String rootElement = parser.getName();
//構建出NavDestination
NavDestination destination = inflate(res, parser, attrs, graphResId);
//合法性檢測
if (!(destination instanceof NavGraph)) {
throw new IllegalArgumentException("Root element <" + rootElement + ">"
+ " did not inflate into a NavGraph");
}
return (NavGraph) destination;
} catch (Exception e) {
throw new RuntimeException("Exception inflating "
+ res.getResourceName(graphResId) + " line "
+ parser.getLineNumber(), e);
} finally {
parser.close();
}
}
上面的inflate方法內部會繼續調用inflate方法。
(1)getNavigator方法獲取都Navigator實例,該實例在構建NavController是被添加進去,這裏獲取的是FragmentNavigator對象。
(2)createDestination方法,會調用FragmentNavigator的createDestination構建Destination對象。
(3)onInflate方法,調用FragmentNavigator.Destination的方法獲取設置的Fragment的類名。
(4)while循環內部通過遞歸構建導航圖。
private NavDestination inflate(Resources res, XmlResourceParser parser, AttributeSet attrs)
throws XmlPullParserException, IOException {
Navigator navigator = mNavigatorProvider.getNavigator(parser.getName());
final NavDestination dest = navigator.createDestination();
dest.onInflate(mContext, attrs);
final int innerDepth = parser.getDepth() + 1;
int type;
int depth;
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& ((depth = parser.getDepth()) >= innerDepth
|| type != XmlPullParser.END_TAG)) {
if (type != XmlPullParser.START_TAG) {
continue;
}
if (depth > innerDepth) {
continue;
}
final String name = parser.getName();
if (TAG_ARGUMENT.equals(name)) {
//解析參數,存儲在dest中
inflateArgument(res, dest, attrs);
} else if (TAG_DEEP_LINK.equals(name)) {
//解析深度鏈接
inflateDeepLink(res, dest, attrs);
} else if (TAG_ACTION.equals(name)) {
//解析Action
inflateAction(res, dest, attrs);
} else if (TAG_INCLUDE.equals(name) && dest instanceof NavGraph) {
//如果子節點爲graph,加載子節點的destination。即通過include方法。
final TypedArray a = res.obtainAttributes(attrs, R.styleable.NavInclude);
final int id = a.getResourceId(R.styleable.NavInclude_graph, 0);
((NavGraph) dest).addDestination(inflate(id));
a.recycle();
} else if (dest instanceof NavGraph) {
//如果子節點爲graph加載子節點的destination
//向每個NavGraph中加入Destination
((NavGraph) dest).addDestination(inflate(res, parser, attrs));
}
}
return dest;
}
- onGraphCreated方法。
通過NavInflater類之後,解析了XML文件構建整個Graph之後。,下面回到setGraph方法,在解析玩XML後會調用setGraph方法。
(1)popBackStackInternal方法將舊的導航圖全部出棧。
(2)調用onGraphCreated主要是顯示一個導航Fragment視圖。
public void setGraph(@NonNull NavGraph graph, @Nullable Bundle startDestinationArgs) {
if (mGraph != null) {
// Pop everything from the old graph off the back stack
popBackStackInternal(mGraph.getId(), true);
}
mGraph = graph;
onGraphCreated(startDestinationArgs);
}
- onGraphCreated方法
(1)恢復之前的導航狀態
(2)調用navigate方法,顯示第一個Fragment。即在Navigation文件裏,屬性app:startDestination的Fragment。所以最終都會走到navigate導航方法。
private void onGraphCreated(@Nullable Bundle startDestinationArgs) {
if (mNavigatorStateToRestore != null) {
ArrayList<String> navigatorNames = mNavigatorStateToRestore.getStringArrayList(
KEY_NAVIGATOR_STATE_NAMES);
if (navigatorNames != null) {
for (String name : navigatorNames) {
Navigator navigator = mNavigatorProvider.getNavigator(name);
Bundle bundle = mNavigatorStateToRestore.getBundle(name);
if (bundle != null) {
navigator.onRestoreState(bundle);
}
}
}
}
if (mBackStackIdsToRestore != null) {
for (int index = 0; index < mBackStackIdsToRestore.length; index++) {
int destinationId = mBackStackIdsToRestore[index];
Bundle args = (Bundle) mBackStackArgsToRestore[index];
NavDestination node = findDestination(destinationId);
if (node == null) {
throw new IllegalStateException("unknown destination during restore: "
+ mContext.getResources().getResourceName(destinationId));
}
if (args != null) {
args.setClassLoader(mContext.getClassLoader());
}
mBackStack.add(new NavBackStackEntry(node, args));
}
mBackStackIdsToRestore = null;
mBackStackArgsToRestore = null;
}
if (mGraph != null && mBackStack.isEmpty()) {
boolean deepLinked = mActivity != null && handleDeepLink(mActivity.getIntent());
if (!deepLinked) {
// Navigate to the first destination in the graph
// if we haven't deep linked to a destination
navigate(mGraph, startDestinationArgs, null, null);
}
}
}
導航
在構建和獲取到NavController對象以及NavGraph之後。,下面是使用它來實現真正的導航了。下面從navigate開始分析。在navigate方法內部會查詢到NavDestination,然後根據不同的Navigator實現頁面導航。
- navigate 方法
(1)如果回退棧爲null返回NavGraph,不爲null返回回退棧中的最後一項。
(2)根據id,獲取對應的NavAction。然後在通過NavAction獲取目的地id。
(4)利用目的地ID屬性,通過findDestination方法,找到準備導航的目的地。
(5)根據導航目的地的名字,調用getNavigator方法,獲取Navigator對象。這裏對應的是FragmentNavigator。
public void navigate(@IdRes int resId, @Nullable Bundle args, @Nullable NavOptions navOptions,
@Nullable Navigator.Extras navigatorExtras) {
NavDestination currentNode = mBackStack.isEmpty()
? mGraph
: mBackStack.getLast().getDestination();
if (currentNode == null) {
throw new IllegalStateException("no current navigation node");
}
@IdRes int destId = resId;
final NavAction navAction = currentNode.getAction(resId);
Bundle combinedArgs = null;
if (navAction != null) {
if (navOptions == null) {
navOptions = navAction.getNavOptions();
}
destId = navAction.getDestinationId();
Bundle navActionArgs = navAction.getDefaultArguments();
if (navActionArgs != null) {
combinedArgs = new Bundle();
combinedArgs.putAll(navActionArgs);
}
}
if (destId == 0 && navOptions != null && navOptions.getPopUpTo() != -1) {
popBackStack(navOptions.getPopUpTo(), navOptions.isPopUpToInclusive());
return;
}
NavDestination node = findDestination(destId);
navigate(node, combinedArgs, navOptions, navigatorExtras);
}
private void navigate(@NonNull NavDestination node, @Nullable Bundle args,
@Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
boolean popped = false;
if (navOptions != null) {
if (navOptions.getPopUpTo() != -1) {
popped = popBackStackInternal(navOptions.getPopUpTo(),
navOptions.isPopUpToInclusive());
}
}
Navigator<NavDestination> navigator = mNavigatorProvider.getNavigator(
node.getNavigatorName());
Bundle finalArgs = node.addInDefaultArgs(args);
NavDestination newDest = navigator.navigate(node, finalArgs,
navOptions, navigatorExtras);
- FragmentNavigator的實現
通過以上的分析,又來到了Navigator 的子類FragmentNavigator類。下面來看看FragmentNavigator.navigate的方法。
(1)調用instantiateFragment,通過反射機制構建Fragment實例
(2)處理進出場等動畫邏輯
(3)最終調用FragmentManager來處理導航邏輯。
猜測ActivityNavigator最終也是調用了startActivity方法,這裏就不展示代碼了。
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;
}
final Fragment 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);
ft.setPrimaryNavigationFragment(frag);
ft.setReorderingAllowed(true);
ft.commit();
}
小結
(1)NavHostFragment 作爲導航載體,在Activity的layout文件裏被引用(或者在代碼中動態),並且持有導航控制類NavController引用。
(2)NavController 將導航任務委託給Navigator類,Navigator類有兩個重要的子類FragmentNavigator和ActivityNavigator子類。NavController類持有NavInflater類引用。
(3)NavInflater 負責解析Navgation文件,負責構建NavGraph導航圖。
(4)NavDestination 存有各個目的地信息,在FragmentNavigator和ActivityNavigator內部分別對應一個Destination類,該類繼承NavDestination。
(5)在頁面導航時,fragment的操作還是交由FragmentManager在操作,activity交由startActivity執行。
下面貼一下,網上總結的比較全的類圖信息:
來自圖片來源