实现多个Fragment依次返回(Fragment回退栈简单使用)
程序员文章站
2022-03-13 16:49:35
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一、情景介绍
首先说下什么情况会用到Fragment的回退栈,假设现在要在一个Activity上不停的切换Fragment(在一个Fragment里不停切换Fragment也可以),但是要求我们可以用安卓的返回键返回上一个Fragment这个时候就要用到Fragment的回退栈了
效果图:
二、详细说明
这个回退栈类似于安卓为Activity维护的任务栈,我们也可以通过Activity维护一个回退栈来保存每次Fragment事务发生的变化。如果你将Fragment任务添加到回退栈,当用户点击后退按钮时,将看到上一次的保存的Fragment。一旦Fragment完全从后退栈中弹出,用户再次点击后退键,则退出当前Activity。 Fragment的生命周期是依赖Activity的,要是用我理解的话说就是Activity是房子的话,那么Fragment就是房子里面的房间了,看下Fragment的生命周期:
三、功能说明和动手操作
要求:
1.我们用一个Activity同时切换3个Fragment
2.需要通过返回键能返回上一个Fragment
实现:
1.每次切换Fragment都将Fragment放入回退栈里面去
2.按返回键依次去取回退栈里面的Fragment
首先我们需要3个Fragment
public class Fragment1 extends Fragment implements View.OnClickListener { @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment1, container, false); TextView mTextView = (TextView) view.findViewById(R.id.tv_fragment_content); mTextView.setText("Fragment1"); Button mButton = (Button) view.findViewById(R.id.btn_toggle_fragment); mButton.setOnClickListener(this); return view; } @Override public void onClick(View view) { Fragment2 f2 = new Fragment2(); FragmentManager mManager = getFragmentManager(); FragmentTransaction ft1 = mManager.beginTransaction(); ft1.addToBackStack(null);//这里将我们的Fragment加入到返回栈 ft1.replace(R.id.lv_fragment_container, f2); ft1.commit(); } }
public class Fragment2 extends Fragment implements View.OnClickListener{
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment1,container,false);
TextView mTextView = (TextView) view.findViewById(R.id.tv_fragment_content);
mTextView.setText("Fragment2");
mTextView.setOnClickListener(this);
Button mButton = (Button) view.findViewById(R.id.btn_toggle_fragment);
mButton.setOnClickListener(this);
return view;
}
@Override
public void onClick(View view) {
Fragment3 f3 = new Fragment3();
FragmentManager fm3 = getFragmentManager();
FragmentTransaction ft3 = fm3.beginTransaction();
ft3.addToBackStack(null);
ft3.replace(R.id.lv_fragment_container,f3);
ft3.commit();
}
}
public class Fragment2 extends Fragment implements View.OnClickListener{
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment1,container,false);
TextView mTextView = (TextView) view.findViewById(R.id.tv_fragment_content);
mTextView.setText("Fragment2");
mTextView.setOnClickListener(this);
Button mButton = (Button) view.findViewById(R.id.btn_toggle_fragment);
mButton.setOnClickListener(this);
return view;
}
@Override
public void onClick(View view) {
Fragment3 f3 = new Fragment3();
FragmentManager fm3 = getFragmentManager();
FragmentTransaction ft3 = fm3.beginTransaction();
ft3.addToBackStack(null);
ft3.replace(R.id.lv_fragment_container,f3);
ft3.commit();
}
}
public class Fragment3 extends Fragment{
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment1,container,false);
TextView mTextView = (TextView) view.findViewById(R.id.tv_fragment_content);
mTextView.setText("Fragment3");
return view;
}
}
//3个Fragment用同一个Xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/tv_fragment_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:textSize="40sp"
android:text="--"
android:layout_weight="1"
/>
<Button
android:id="@+id/btn_toggle_fragment"
android:layout_width="match_parent"
android:layout_height="40dp"
android:text="toggle"
/>
</LinearLayout>
//3个Fragment用同一个Xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/tv_fragment_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:textSize="40sp"
android:text="--"
android:layout_weight="1"
/>
<Button
android:id="@+id/btn_toggle_fragment"
android:layout_width="match_parent"
android:layout_height="40dp"
android:text="toggle"
/>
</LinearLayout>
核心代码:
public class MainActivity extends FragmentActivity {
private Fragment f1;
@Override
protected void onCreate( Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Window mWindow = getWindow();
mWindow.setContentView(R.layout.fragment_layout);
f1 = new Fragment1();
getSupportFragmentManager().beginTransaction().add(R.id.lv_fragment_container,f1,"first").commit();
}
@Override
public void onBackPressed() {
Toast.makeText(MainActivity.this, "left count:"+getSupportFragmentManager().getBackStackEntryCount(), Toast.LENGTH_SHORT).show();
if(getSupportFragmentManager().getBackStackEntryCount() <= 0)//这里是取出我们返回栈存在Fragment的个数
finish();
else
getSupportFragmentManager().popBackStack();
//取出我们返回栈保存的Fragment,这里会从栈顶开始弹栈
}
}
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