Android 保存Fragment 切换状态实例代码

前言

 一般频繁切换fragment会导致频繁的释放和创建，如果fragment比较臃肿体验就非常不好了，这里分享一个方法。

 正文

 一、应用场景

  1、不使用viewpager

  2、不能用replace来切换fragment，会导致fragment释放（调用ondestroyview）

 二、实现

1、xml

<linearlayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical" >

 <framelayout
  android:id="@+id/container"
  android:layout_width="match_parent"
  android:layout_height="0dip"
  android:layout_weight="1.0" >
 </framelayout>

 <radiogroup
  android:id="@+id/main_radio"
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:layout_gravity="bottom"
  android:gravity="bottom"
  android:layout_marginbottom="-6dp"
  android:orientation="horizontal" >

  <radiobutton
   android:id="@+id/radio_button0"
   style="@style/main_tab_bottom"
   android:drawabletop="@drawable/bottom_1" />

  <radiobutton
   android:id="@+id/radio_button1"
   style="@style/main_tab_bottom"
   android:drawabletop="@drawable/bottom_2" />

  <radiobutton
   android:id="@+id/radio_button2"
   style="@style/main_tab_bottom"
   android:drawabletop="@drawable/bottom_3" />

  <radiobutton
   android:id="@+id/radio_button3"
   style="@style/main_tab_bottom"
   android:drawabletop="@drawable/bottom_4" />

  <radiobutton
   android:id="@+id/radio_button4"
   style="@style/main_tab_bottom"
   android:drawabletop="@drawable/bottom_5" />
 </radiogroup>

</linearlayout>

代码说明：

    非常常见的底部放5个radiobutton，点击切换不同的fragment。

  2、activity

   为radiobutton设置setoncheckedchangelistener事件，其他代码:

 public void oncheckedchanged(compoundbutton buttonview, boolean ischecked) {
  if (ischecked) {
   fragment fragment = (fragment) mfragmentpageradapter.instantiateitem(mcontainer, buttonview.getid());
   mfragmentpageradapter.setprimaryitem(mcontainer, 0, fragment);
   mfragmentpageradapter.finishupdate(mcontainer);
  } 
 }

 private fragmentpageradapter mfragmentpageradapter = new fragmentpageradapter(getsupportfragmentmanager()) {

  @override
  public fragment getitem(int position) {
   switch (position) {
   case r.id.radio_button1:
    return new fragment1();
   case r.id.radio_button2:
    return new fragment2();
   case r.id.radio_button3:
    return new fragment3();
   case r.id.radio_button4:
    return new fragment4();
   case r.id.radio_button0:
   default:
    return new fragment0();
   }
  }

  @override
  public int getcount() {
   return 5;
  }
 };

代码说明：

   instantiateitem从fragmentmanager中查找fragment，找不到就getitem新建一个，setprimaryitem设置隐藏和显示，最后finishupdate提交事务， mcontainer就是xml中的framelayout。

 三、fragmentpageradapter核心代码

 @override
 public object instantiateitem(viewgroup container, int position) {
  if (mcurtransaction == null) {
   mcurtransaction = mfragmentmanager.begintransaction();
  }

  final long itemid = getitemid(position);

  // do we already have this fragment?
  string name = makefragmentname(container.getid(), itemid);
  fragment fragment = mfragmentmanager.findfragmentbytag(name);
  if (fragment != null) {
   if (debug) log.v(tag, "attaching item #" + itemid + ": f=" + fragment);
   mcurtransaction.attach(fragment);
  } else {
   fragment = getitem(position);
   if (debug) log.v(tag, "adding item #" + itemid + ": f=" + fragment);
   mcurtransaction.add(container.getid(), fragment,
     makefragmentname(container.getid(), itemid));
  }
  if (fragment != mcurrentprimaryitem) {
   fragment.setmenuvisibility(false);
   fragment.setuservisiblehint(false);
  }

  return fragment;
 }

 @override
 public void destroyitem(viewgroup container, int position, object object) {
  if (mcurtransaction == null) {
   mcurtransaction = mfragmentmanager.begintransaction();
  }
  if (debug) log.v(tag, "detaching item #" + getitemid(position) + ": f=" + object
    + " v=" + ((fragment)object).getview());
  mcurtransaction.detach((fragment)object);
 }

 @override
 public void setprimaryitem(viewgroup container, int position, object object) {
  fragment fragment = (fragment)object;
  if (fragment != mcurrentprimaryitem) {
   if (mcurrentprimaryitem != null) {
    mcurrentprimaryitem.setmenuvisibility(false);
    mcurrentprimaryitem.setuservisiblehint(false);
   }
   if (fragment != null) {
    fragment.setmenuvisibility(true);
    fragment.setuservisiblehint(true);
   }
   mcurrentprimaryitem = fragment;
  }
 }

 @override
 public void finishupdate(viewgroup container) {
  if (mcurtransaction != null) {
   mcurtransaction.commitallowingstateloss();
   mcurtransaction = null;
   mfragmentmanager.executependingtransactions();
  
} 
 public void setmenuvisibility(boolean menuvisible) {
        super.setmenuvisibility(menuvisible);
        if (this.getview() != null)
            this.getview().setvisibility(menuvisible ? view.visible : view.gone);
    }
 }

fragmentpageradapter是support包自带的类。

四、注意

  之前自己模拟viewpager用attach、setmenuvisibility、setuservisiblehint来控制fragment的显示隐藏，经常会出现fragment重叠现象，非常头疼，换了这个之后目前没有发现重叠现象。

 结束：以上就是对android fragment 实例说明，希望能帮助有需要的同学。