一.概述
1.概念:
Fragment是Activity的一個組成片段,不能獨立存在,必須嵌入到Activity,在Activity運行時進行添加和刪除。
它具有自己的生命週期,但受宿主Activity生命週期的影響。
2.意義:
Fragment可以緩解 Activity 任務過重的問題,處理在不同屏幕上 UI 組件的佈局問題。
官方文檔:https://developer.android.com/guide/components/fragments.html?hl=zh-cn
二.Fragment的生命週期
Fragment生命週期圖:
方法 | 說明 |
---|---|
onAttach() | Fragment與Activity關聯時調用 |
onCreateView() | 創建Fragment視圖 |
onActivityCreated() | Activity的onCreate()方法返回時調用 |
onDestroyView() | Fragment的視圖移除時調用 |
onDetach() | 取消Fragment和Activity關聯時調用 |
Activity和Fragment生命週期對比圖:
三.Fragment的使用方法
向Activity中添加Fragment有兩種方法:
1.在Activity的佈局文件中靜態添加:
很簡單,以在Activity中添加一個Fragment爲例:
Activity的佈局文件:
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.liuwei.fragmentdemo.StaticAddActivity">
<fragment
android:id="@+id/activity_second_fragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:name="com.example.liuwei.fragmentdemo.FragmentTest"/>
</LinearLayout>
佈局文件fragment標籤中的 android:name 屬性需要指定要在佈局中實例化的 Fragment 類,android:id 屬性提供唯一 ID或android:tag 屬性提供唯一字符串。
添加的Fragment的佈局文件:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="這是一個Fragment"
android:gravity="center"/>
</LinearLayout>
繪製添加的Fragment的視圖。
Fragment文件:
public class FragmentTest extends Fragment{
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_test, null);
return view;
}
}
在onCreateView()方法中初始化Fragment佈局文件。
2.在代碼中動態添加:
(1)主要步驟:
Activity的佈局文件:
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.liuwei.fragmentdemo.DynamicAddActivity">
<FrameLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent">
</FrameLayout>
</RelativeLayout>
Activity中動態添加Fragment代碼:
FragmentManager manager = getFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
Fragment fragment = new OneFragment();
transaction.add(R.id.container, fragment);
transaction.commit();
通過“container”id,將fragment動態添加到Activity中。
FragmentTransaction:
FragmentTransaction transaction = manager.beginTransaction();表示開啓一個事務。
方法 | 說明 |
---|---|
transaction.add() | 添加fragment |
transaction.remove() | 移除fragment |
transaction.replace() | 替換fragment,會將上一個Fragment銷燬 |
transaction.hide() | 隱藏fragment,不可見但未銷燬 |
transaction.show() | 顯示fragment |
addToBackStack() | 添加當前事務到回退棧中,即當按下返回鍵時,界面迴歸到當前事物狀態 |
transaction.commit() | 提交事務 |
(2)動態添加Fragment的完整案例:
其中Activity.java:
public class DynamicAddActivity extends Activity implements View.OnClickListener{
private TextView one_tv;
private TextView two_tv;
private TextView three_tv;
private TextView four_tv;
private OneFragment oneFragment;
private TwoFragment twoFragment;
private ThreeFragment threeFragment;
private FourFragment fourFragment;
private FragmentManager manager;
private FragmentTransaction transaction;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_dynamic_add);
initView();
manager = getFragmentManager();
}
private void initView(){
one_tv = (TextView) this.findViewById(R.id.one_tv);
two_tv = (TextView) this.findViewById(R.id.two_tv);
three_tv = (TextView) this.findViewById(R.id.three_tv);
four_tv = (TextView) this.findViewById(R.id.four_tv);
one_tv.setOnClickListener(this);
two_tv.setOnClickListener(this);
three_tv.setOnClickListener(this);
four_tv.setOnClickListener(this);
}
@Override
public void onClick(View view) {
switch(view.getId()){
case R.id.one_tv:
switchFragment(1);
break;
case R.id.two_tv:
switchFragment(2);
break;
case R.id.three_tv:
switchFragment(3);
break;
case R.id.four_tv:
switchFragment(4);
break;
}
}
private void switchFragment(int index){
transaction = manager.beginTransaction();
hideFragment(transaction);
switch(index){
case 1:
if(oneFragment == null){
oneFragment = new OneFragment();
transaction.add(R.id.container, oneFragment);
} else {
transaction.show(oneFragment);
}
break;
case 2:
if(twoFragment == null){
twoFragment = new TwoFragment();
transaction.add(R.id.container, twoFragment);
} else {
transaction.show(twoFragment);
}
break;
case 3:
if(threeFragment == null){
threeFragment = new ThreeFragment();
transaction.add(R.id.container, threeFragment);
} else {
transaction.show(threeFragment);
}
break;
case 4:
if(fourFragment == null){
fourFragment = new FourFragment();
transaction.add(R.id.container, fourFragment);
} else {
transaction.show(fourFragment);
}
break;
}
transaction.commit();
}
private void hideFragment(FragmentTransaction transaction){
if(oneFragment != null){
transaction.hide(oneFragment);
}
if(twoFragment != null){
transaction.hide(twoFragment);
}
if(threeFragment != null){
transaction.hide(threeFragment);
}
if(fourFragment != null){
transaction.hide(fourFragment);
}
}
}
完整代碼請點擊這裏。