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">
<LinearLayout
android: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>
<LinearLayout
android: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"?>
<TextView
xmlns: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"?>
<TextView
xmlns: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? = null
var replaceLl : LinearLayout? = null
var 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? LinearLayout
replaceLl = findViewById(R.id.replace_child_ll) as? LinearLayout
mMainHandler.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? LinearLayout
replaceLl = findViewById(R.id.replace_child_ll) as? LinearLayout
mMainHandler.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 = 0
supportFragmentManager.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
