在SO中多次询问这类问题，我已经尝试了所有这些问题，但无法达到我真正想要的效果。在我的应用中，我有Fragment，在该片段中我有recycler视图，recyclerview将由我从API获取的数据操纵。我希望在轮换更改时，应用程序不会再次调用API。为了达到这个目的，我知道我必须将数据放在onSaveInstanceState中，如果我想保存一个复杂的对象，那么该类必须是实现Parcelable。我已经做了所有推荐的事情，但无法实现我想要的目标。
我在这里分享我的代码，我创建了一个简化的例子，我真正想做的事情。
SimpleFragment.java
的代码public class SimpleFragment extends Fragment {
RecyclerView recyclerView;
ArrayList<TestModel> testModelList = new ArrayList<TestModel>() ;
SimpleAdapter simpleAdapter;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.simple_fragment, container, false);
recyclerView = (RecyclerView) rootView.findViewById(R.id.recycler);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
recyclerView.setLayoutManager(mLayoutManager);
simpleAdapter = new SimpleAdapter(getActivity());
recyclerView.setAdapter(simpleAdapter);
if(savedInstanceState != null){
//if this fragment starts after a rotation or configuration change, load the existing model from a parcelable
testModelList = savedInstanceState.getParcelableArrayList("key");
// I have done necessary debug , after rotation , it comes here ,
// but suddenly savedInstanceState becomes null and getTestModelList() get called
}else {
//if this fragment starts for the first time, load the list of model
getTestModelList();
}
simpleAdapter.setModel(testModelList);
return rootView;
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putParcelableArrayList("key",testModelList);
}
public void getTestModelList(){
for (int i=0;i<10;i++){
testModelList.add(new TestModel(i,"test"+i));
}
Toast.makeText(getActivity(),"Called",Toast.LENGTH_SHORT).show();
}
}
SimpleFragment的布局文件： simple_fragment.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">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler"
android:background="@android:color/black"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
以下是我的数据模型 TestModel.java
的代码public class TestModel implements Parcelable {
String text;
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
public TestModel(int number, String text) {
this.text = text;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.text);
}
protected TestModel(Parcel in) {
this.text = in.readString();
}
public static final Parcelable.Creator<TestModel> CREATOR
= new Parcelable.Creator<TestModel>() {
public TestModel createFromParcel(Parcel in) {
return new TestModel(in);
}
public TestModel[] newArray(int size) {
return new TestModel[size];
}
};
}
我的适配器类： SimpleAdapter.java
public class SimpleAdapter extends RecyclerView.Adapter<SimpleAdapter.ViewHolder> {
Context context;
ArrayList<TestModel> testModels;
public SimpleAdapter(Context context) {
this.context = context;
}
public void setModel(ArrayList<TestModel> model){
this.testModels = model;
notifyDataSetChanged();
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.single_row, viewGroup, false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
holder.list_item.setText(testModels.get(position).getText());
}
@Override
public int getItemCount() {
return testModels.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
TextView list_item;
public ViewHolder(View itemView) {
super(itemView);
list_item = (TextView) itemView.findViewById(R.id.list_item);
}
}
}
适配器 single_row.xml
的单行布局代码<?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:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="20dp"
android:id="@+id/list_item"
android:textColor="@android:color/white"/>
</LinearLayout>
这些是我所做的，如果再次调用我的SimpleFragment中的方向getTestModelList()方法，我想避免，在实际的应用场景中，此方法将执行一些API调用。我想保存ArrayList<TestModel> testModelList的状态。
任何帮助都将受到高度赞赏。提前谢谢。
答案 0 :(得分：2)
您需要保存活动状态并在配置之前进行检查
按照此代码
public class MainActivity extends AppCompatActivity{
private HomeFragment homeFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FragmentManager fm = getSupportFragmentManager();
if (savedInstanceState == null) {
homeFragment = new HomeFragment();
((fm.beginTransaction()).replace(R.id.mainframe, homeFragment)).commit();
}
}}}
答案 1 :(得分：2)
您可以在Fragment onCreate方法中保存像这样的Fragment实例，以便更改方向以保存实例：
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Set Instance true
this.setRetainInstance(true);
}
答案 2 :(得分：1)