XML文件
Activity布局文件R.layout.activity_main
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:id="@+id/root_ll"android:orientation="vertical"android:layout_width="match_parent"android:layout_height="match_parent"><LinearLayoutandroid:id="@+id/add_child_ll"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:background="@android:color/holo_green_light"android:gravity="center"android:orientation="vertical"></LinearLayout><LinearLayoutandroid:id="@+id/replace_child_ll"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:background="@android:color/holo_red_light"android:gravity="center"android:orientation="vertical"></LinearLayout>
</LinearLayout>
- 第一次添加的
MyFragmentA布局R.layout.inflate_layout_a
<?xml version="1.0" encoding="utf-8"?>
<TextViewxmlns:android="http://schemas.android.com/apk/res/android"android:id="@+id/inflate_tv_a"android:layout_width="match_parent"android:layout_height="100dp"android:background="@android:color/holo_blue_light" />
- 第二次添加的
MyFragmentB布局R.layout.inflate_layout_b
<?xml version="1.0" encoding="utf-8"?>
<TextViewxmlns:android="http://schemas.android.com/apk/res/android"android:id="@+id/inflate_tv_b"android:layout_width="match_parent"android:layout_height="100dp"android:background="@android:color/holo_orange_light"/>
Activtiy代码和Fragment代码
-MyFragmentA代码
class MyFragmentA : Fragment() {override fun onCreateView(inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?): View? {return inflater.inflate(R.layout.inflate_layout_a, container, false)}
}
-MyFragmentB代码
class MyFragmentB : Fragment() {override fun onCreateView(inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?): View? {return inflater.inflate(R.layout.inflate_layout_b, container, false)}
}
Activity代码
const val TAG = "Yang"
class MainActivity : AppCompatActivity() {var addLl : LinearLayout? = nullvar replaceLl : LinearLayout? = nullvar mMainHandler = Handler(Looper.getMainLooper())override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(R.layout.activity_main)addLl = findViewById(R.id.add_child_ll) as? LinearLayoutreplaceLl = findViewById(R.id.replace_child_ll) as? LinearLayoutmMainHandler.postDelayed({val firstFragment1 = MyFragmentA()val firstFragment2 = MyFragmentA()addLl?.let {replaceFragment(firstFragment1, it)}replaceLl?.let {replaceFragment(firstFragment2, it)}}, 3000)mMainHandler.postDelayed({val secondFragment1 = MyFragmentB()val secondFragment2 = MyFragmentB()addLl?.let {addFragment(secondFragment1, it)}replaceLl?.let {replaceFragment(secondFragment2, it)}}, 6000)}private fun addFragment(fragment: Fragment, targetView: View) {val transaction = supportFragmentManager.beginTransaction()transaction?.add(targetView.id, fragment)?.commitNowAllowingStateLoss()}private fun replaceFragment(fragment: Fragment, targetView: View) {val transaction = supportFragmentManager.beginTransaction()transaction?.replace(targetView.id, fragment)?.commitNowAllowingStateLoss()}
}
- 3s后通过
replace()方法在两个LinearLayout中以居中方式添加蓝色背景的MyFragmentA，MyFragmentA的background不会覆盖掉原有Activity的background - 6s后通过
add()方法在R.id.add_child_ll的LinearLayout中以居中方式添加橘色背景的MyFragmentB，add()方法添加并不会移除覆盖掉第一次添加的MyFragmentA的background。因为不会移除，所以橘色背景的MyFragmentB在第一次添加的MyFragmentA的background下方继续布局绘制 - 6s后通过
replace()方法在R.id.replace_child_ll的LinearLayout中以居中方式添加橘色背景的MyFragmentB，add()方法添加会移除覆盖掉第一次添加的MyFragmentA的background。因为会移除，所以橘色背景的MyFragmentB直接在原有R.id.replace_child_ll的LinearLayout中直接居中布局绘制 - 如果只是将新的
Fragment添加到Activity，而不关心或者不需要移除已存在的Fragment，使用add()方法。但是如果希望替换container中已存在的Fragment，使用replace()方法
获取当前Fragment的数量
- 获取
Activity中Fragment的数量
override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)Log.i(TAG, "onCreate")setContentView(R.layout.activity_main)addLl = findViewById(R.id.add_child_ll) as? LinearLayoutreplaceLl = findViewById(R.id.replace_child_ll) as? LinearLayoutmMainHandler.postDelayed({val firstFragment1 = MyFragmentA()val firstFragment2 = MyFragmentA()addLl?.let {replaceFragment(firstFragment1, it)}replaceLl?.let {replaceFragment(firstFragment2, it)}Log.i(TAG, "3000ms Number of fragments: ${supportFragmentManager.fragments.size}")Log.i(TAG, "addLl active fragment count = ${addLl?.let { getActiveFragmentCount(it) }} ")Log.i(TAG, "replaceLl active fragment count = ${replaceLl?.let { getActiveFragmentCount(it) }} ")}, 3000)mMainHandler.postDelayed({val secondFragment1 = MyFragmentB()val secondFragment2 = MyFragmentB()addLl?.let {addFragment(secondFragment1, it)}replaceLl?.let {replaceFragment(secondFragment2, it)}Log.i(TAG, "6000ms Number of fragments: ${supportFragmentManager.fragments.size}")Log.i(TAG, "addLl active fragment count = ${addLl?.let { getActiveFragmentCount(it) }} ")Log.i(TAG, "replaceLl active fragment count = ${replaceLl?.let { getActiveFragmentCount(it) }} ")}, 6000)}// log result
// 3s添加了两个MyFragmentA，数量为2
// 6s添加两个MyFragmentB，移除一个MyFragmentA，数量为3
2024-06-06 11:11:31.427 24538-24538 Yang I 3000ms Number of fragments: 2
2024-06-06 11:11:34.423 24538-24538 Yang I 6000ms Number of fragments: 3
- 获取
View中Fragment的数量
fun getActiveFragmentCount(view : View): Int {var count = 0supportFragmentManager.fragments.forEach {if(it.view?.parent == view){count++}}return count
}// log result
// 3s添加了两个LinearLayout各自添加一个Fragment
2024-06-06 12:57:55.747 24983-24983 Yang I 3000ms Number of fragments: 2
2024-06-06 12:57:55.747 24983-24983 Yang I addLl active fragment count = 1
2024-06-06 12:57:55.747 24983-24983 Yang I replaceLl active fragment count = 1
// 6s第一个LinearLayout通过add方式添加，
2024-06-06 12:57:58.739 24983-24983 Yang I 6000ms Number of fragments: 3
2024-06-06 12:57:58.740 24983-24983 Yang I addLl active fragment count = 2
2024-06-06 12:57:58.740 24983-24983 Yang I replaceLl active fragment count = 1
效果图
