我在Android开发方面相当新，所以请耐心等待。我相信我的谷歌地图api实现的实例状态保存有一些问题。我正在使用Android Studio。我正在实现AppCompactActivity来设置选项卡视图。我正在使用FragmentStatePagerAdapter在寻呼机视图中更改片段。我的问题是我的谷歌地图api在非常特殊的情况下不会保存状态。如果我点击距离我的MapFragment索引> 1索引的标签，地图片段的状态将不会被保留，我无法将标记或Go Home按钮添加到地图，但地图已存在。
我的初始标记和家庭位置按钮有效，它只是不会显示备份/允许我在切换到我的上一个标签并切换回地图选项卡后添加更多标记。
正如我所说的，我是android dev的新手，所以任何建议都是值得赞赏的。
这是我的主要活动
public class MainActivity extends AppCompatActivity{
public static FragmentManager fragmentManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentManager = getSupportFragmentManager();
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
tabLayout.addTab(tabLayout.newTab().setText("Tab 1"));
tabLayout.addTab(tabLayout.newTab().setText("Map"));
tabLayout.addTab(tabLayout.newTab().setText("Tab 2"));
tabLayout.addTab(tabLayout.newTab().setText("Tab 3"));
tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
final PagerAdapter adapter = new PagerAdapter
(getSupportFragmentManager(), tabLayout.getTabCount());
viewPager.setAdapter(adapter);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
return super.onOptionsItemSelected(item);
}
}
主要活动xml为
<RelativeLayout
android:id="@+id/main_layout"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:background="?attr/colorPrimary"
android:elevation="6dp"
android:minHeight="?attr/actionBarSize"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>
<android.support.design.widget.TabLayout
android:id="@+id/tab_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/toolbar"
android:background="?attr/colorPrimary"
android:elevation="6dp"
android:minHeight="?attr/actionBarSize"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"/>
<android.support.v4.view.ViewPager
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="fill_parent"
android:layout_below="@id/tab_layout"/>
</RelativeLayout>
这是我的PagerAdapter类
public class PagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;
public PagerAdapter(FragmentManager fm, int NumOfTabs) {
super(fm);
this.mNumOfTabs = NumOfTabs;
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new TabFragment1();
case 1:
return new MapViewFragment();
case 2:
return new TabFragment2();
case 3:
return new TabFragment3();
default:
return null;
}
}
@Override
public int getCount() {
return mNumOfTabs;
}
}
这是我的MapFragment类
public class MapViewFragment extends Fragment {
private static View view;
/**
* Note that this may be null if the Google Play services APK is not
* available.
*/
private static GoogleMap mMap;
private static Double latitude, longitude;
private static String quickFilterText="";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (container == null) {
return null;
}
view = inflater.inflate(R.layout.activity_maps, container, false);
// Passing harcoded values for latitude & longitude. Please change as per your need. This is just used to drop a Marker on the Map
latitude = 26.78;
longitude = 72.56;
ImageButton arrowButton = (ImageButton) view.findViewById(R.id.arrowButton);
arrowButton.setOnClickListener(new ImageButton.OnClickListener() {
public void onClick(View newView) {
RelativeLayout relLayout = (RelativeLayout) view.findViewById(R.id.filterDropDown);
EditText text = (EditText) view.findViewById(R.id.quickFilter);
try
{
quickFilterText = text.getText().toString();
}
catch(Exception err)
{
}
if(relLayout.getHeight()>0)
{
relLayout.setLayoutParams(new RelativeLayout.LayoutParams(relLayout.getWidth(),0));
}
else
{
relLayout.setLayoutParams(new RelativeLayout.LayoutParams(relLayout.getWidth(),180));
}
}
});
return view;
}
/***** Sets up the map if it is possible to do so *****/
public void setUpMapIfNeeded() {
// Do a null check to confirm that we have not already instantiated the map.
if (mMap == null) {
// Try to obtain the map from the SupportMapFragment.
mMap = ((SupportMapFragment) getChildFragmentManager()
.findFragmentById(R.id.map)).getMap();
// Check if we were successful in obtaining the map.
if (mMap != null)
setUpMap();
}
}
/**
* This is where we can add markers or lines, add listeners or move the
* camera.
* <p>
* This should only be called once and when we are sure that {@link #mMap}
* is not null.
*/
private static void setUpMap() {
// For showing a move to my loction button
mMap.setMyLocationEnabled(true);
// For dropping a marker at a point on the Map
mMap.addMarker(new MarkerOptions().position(new LatLng(latitude, longitude)).title("My Home").snippet("Home Address"));
// For zooming automatically to the Dropped PIN Location
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(latitude,
longitude), 12.0f));
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
// TODO Auto-generated method stub
setUpMapIfNeeded();
if (mMap == null) {
// Try to obtain the map from the SupportMapFragment.
mMap = ((SupportMapFragment) getChildFragmentManager()
.findFragmentById(map)).getMap(); // getMap is deprecated
// Check if we were successful in obtaining the map.
if (mMap != null)
setUpMap();
}
setRetainInstance(true);
}
/**** The mapfragment's id must be removed from the FragmentManager
**** or else if the same it is passed on the next time then
**** app will crash ****/
@Override
public void onDestroy(){
super.onDestroy();
}
@Override
public void onResume() {
super.onResume();
setUpMapIfNeeded();
}
}
这是我的activity_maps.xml
<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=".MapActivity">
<fragment 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"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment" />
<RelativeLayout
android:id="@+id/filterDropDown"
android:layout_width="match_parent"
android:layout_height="0dp"
android:orientation="horizontal"
android:background="#80000000"
android:gravity="top|center"
android:padding="4dp"
android:weightSum="1">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:paddingLeft="8dp"
android:text="Filter"
android:id="@+id/filterTextBox"
android:gravity="center_vertical" />
<EditText
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/quickFilter"
android:paddingRight="8dp"
android:paddingLeft="8dp"
android:layout_toRightOf="@+id/filterTextBox" />
</RelativeLayout>
</RelativeLayout>
<RelativeLayout
android:id="@+id/arrow"
android:layout_width="70dp"
android:layout_height="23dp"
android:orientation="horizontal"
android:background="@drawable/shape"
android:gravity="center"
android:padding="4dp"
android:layout_gravity="center_horizontal|top"
android:weightSum="1"
android:layout_centerHorizontal="true"
android:layout_below="@+id/filterDropDown">
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Filter"
android:id="@+id/arrowButton"
android:background="@drawable/down_arrow"
android:clickable="true" />
</RelativeLayout>
</RelativeLayout>
我的其他3个标签只是简单的片段，里面有文本视图
public class TabFragment1 extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.tab_fragment_1, container, false);
}
}
布局
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="Tab 1"
android:textAppearance="?android:attr/textAppearanceLarge"/>
</RelativeLayout>
答案 0 :(得分：2)
默认情况下，视图寻呼机保留当前片段，并且其左侧和右侧的一个片段保持活动状态。在您的寻呼机适配器中，您告诉它创建一个全新的片段，而不是使用现有的片段。
List<Fragment> myPages; // populate this in the constructor
@Override
public Fragment getItem(int position) {
return myPages.get(position);
}
@Override
public int getCount() {
return myPages.size();
}
如果您知道只有这四个片段，您还应该增加屏幕外页面限制。
viewPager.setOffscreenPageLimit(3);
如果在执行这两项操作后遇到更多地图问题，您可能需要设置地图片段以保留其实例状态。覆盖片段onCreate()方法。
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}