我有一个 Android 应用程序,它有两个 fragment ,将数据从 fragment A 传递到 fragment B。我可以正确加载所有数据,但是当我更改屏幕方向时,所有数据都会重新加载。我已经在要保留状态的 fragment 中设置了 onSaveInstanceState
和 onViewStateRestored
方法,但当屏幕方向发生变化时,什么都不会保留。
需要解决的主要问题是当文本加载到 FragmentB 中的 TextView 时 - 当屏幕方向更改时它需要保留在那里。
MainActivity.Java
package com.example.tourguide;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentTransaction;
public class MainActivity extends AppCompatActivity implements FragmentA.FragmentAListener, FragmentB.FragmentBListener {
private FragmentA fragmentA;
private FragmentB fragmentB;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentA = new FragmentA();
fragmentB = new FragmentB();
if(savedInstanceState == null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container_a, new FragmentA());
ft.replace(R.id.container_b, new FragmentB());
ft.commitNow();
}
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
}
@Override
protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
}
@Override
public void onInputASent(CharSequence input) {
fragmentB.updateEditText(input);
}
@Override
public void onInputBSent(CharSequence input) {
fragmentA.updateEditText(input);
}
}
FragmentA.Java
package com.example.tourguide;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.ListFragment;
public class FragmentA extends ListFragment implements AdapterView.OnItemClickListener {
private FragmentAListener listener;
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String[] locationList = getActivity().getResources().getStringArray(R.array.location_list);
updateEditText(locationList[position]);
listener.onInputASent(locationList[position]);
}
public interface FragmentAListener {
void onInputASent(CharSequence input);
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_a, container, false);
return v;
}
@Override
public void onListItemClick(@NonNull ListView l, @NonNull View v, int position, long id) {
super.onListItemClick(l, v, position, id);
}
public void updateEditText(CharSequence newText) {
//editText.setText(newText);
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof FragmentAListener) {
listener = (FragmentAListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement FragmentAListener");
}
}
@Override
public void onDetach() {
super.onDetach();
listener = null;
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
ArrayAdapter arrayAdapter = ArrayAdapter.createFromResource(getActivity(), R.array.location_list, android.R.layout.simple_list_item_1);
setListAdapter(arrayAdapter);
getListView().setOnItemClickListener(this);
}
}
FragmentB.Java - 这是屏幕旋转时需要将字符串保留在 TextView 内的 fragment
package com.example.tourguide;
import android.content.Context;
import android.content.res.Resources;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
public class FragmentB extends Fragment {
private FragmentBListener listener;
private TextView resultsFrag;
private static final String KEY_TITLE = "title_key";
private String stateObject;
public interface FragmentBListener {
void onInputBSent(CharSequence input);
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_b, container, false);
resultsFrag = v.findViewById(R.id.tvFragmentB);
//I used the same if block in three different locations and none of them worked
if (savedInstanceState != null) {
String itemTo = savedInstanceState.getString(KEY_TITLE);
resultsFrag.setText(itemTo);
} else {
Toast.makeText(getActivity(), "Error 1", Toast.LENGTH_SHORT).show();
}
return v;
}
public void updateEditText(CharSequence newText) {
String newOption = newText.toString();
stateObject = newText.toString();
Resources res = getResources();
String[] locationDesc = res.getStringArray(R.array.location_description);
if (newOption.equals("Calgary")) {
resultsFrag.setText(locationDesc[0]);
} else if (newOption.equals("Victoria")) {
resultsFrag.setText(locationDesc[1]);
} else if (newOption.equals("Vancouver")) {
resultsFrag.setText(locationDesc[2]);
} else if (newOption.equals("Toronto")) {
resultsFrag.setText(locationDesc[3]);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof FragmentBListener) {
listener = (FragmentBListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement FragmentBListener");
}
}
@Override
public void onDetach() {
super.onDetach();
listener = null;
}
@Override
public void onSaveInstanceState(@NonNull Bundle outState) {
super.onSaveInstanceState(outState);
outState.putString(KEY_TITLE, resultsFrag.getText().toString());
}
@Override
public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
super.onViewStateRestored(savedInstanceState);
//I used the same if block in three different locations and none of them worked
if (savedInstanceState != null) {
String itemTo = savedInstanceState.getString(KEY_TITLE);
resultsFrag.setText(itemTo);
} else {
Toast.makeText(getActivity(), "Error 2", Toast.LENGTH_SHORT).show();
}
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
//I used the same if block in three different locations and none of them worked
if (savedInstanceState != null) {
String itemTo = savedInstanceState.getString(KEY_TITLE);
resultsFrag.setText(itemTo);
} else {
Toast.makeText(getActivity(), "Error 3", Toast.LENGTH_SHORT).show();
}
}
}
fragment_b.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/holo_blue_light"
android:gravity="center_horizontal"
android:orientation="vertical"
android:padding="16dp">
<TextView
android:id="@+id/tvFragmentB"
android:layout_width="match_parent"
android:layout_height="602dp" />
</LinearLayout>
字符串
<resources>
<string name="app_name">Tour Guide</string>
<string-array name="location_list">
<item>Calgary</item>
<item>Victoria</item>
<item>Vancouver</item>
<item>Toronto</item>
</string-array>
<!-- Descriptions for the locations -->
<string-array name="location_description">
<item>This is a big description for CALGARY - THIS needs to load in for more information regarding CALGARY</item>
<item>This is a big description for VICTORIA - THIS needs to load in for more information regarding VICTORIA</item>
<item>This is a big description for VANCOUVER - THIS needs to load in for more information regarding VANCOUVER</item>
<item>This is a big description for TORONTO - THIS needs to load in for more information regarding TORONTO</item>
</string-array>
</resources>
fragment_a.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/holo_green_light"
android:gravity="center_horizontal"
android:orientation="vertical"
android:padding="16dp">
<ListView
android:id="@android:id/list"
android:layout_width="wrap_content"
android:layout_height="206dp" />
</LinearLayout>
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:orientation="vertical"
tools:context=".MainActivity">
<FrameLayout
android:id="@+id/container_a"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<FrameLayout
android:id="@+id/container_b"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
最佳答案
它们已保存,但您正在替换它们。使用这个
if(savedInstanceState == null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container_a, new FragmentA());
ft.replace(R.id.container_b, new FragmentB());
ft.commit();
}
请注意, fragment 实例化几乎是此检查产生正确且预期结果的唯一场景。
不要保留对 Fragment 的引用,除非它是通过 findFragmentByTag
+ 实例化获得的。在这种情况下,您可能需要使用 commitNow
来获得可靠的结果。
编辑:更新为更完整的代码:
public class MainActivity extends AppCompatActivity implements FragmentA.FragmentAListener, FragmentB.FragmentBListener {
private FragmentA fragmentA;
private FragmentB fragmentB;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(savedInstanceState == null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container_a, new FragmentA(), "fragmentA");
ft.replace(R.id.container_b, new FragmentB(), "fragmentB");
ft.commitNow();
}
fragmentA = getSupportFragmentManager().findFragmentByTag("fragmentA");
fragmentB = getSupportFragmentManager().findFragmentByTag("fragmentB");
}
关于java - 在 Android 上,带有 fragment 的 Save-Bundle 不保存状态,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/60660909/