我的主要活动包含2个片段：
MainActivity
public class MainActivity extends AppCompatActivity implements FragmentOne.OnFragmentOneInteractionListener, FragmentTwo.OnFragmentTwoInteractionListener{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Check that the activity is using the layout version with
// the fragment_container FrameLayout
if (findViewById(R.id.fragment_container) != null) {
// However, if we're being restored from a previous state,
// then we don't need to do anything and should return or else
// we could end up with overlapping fragments.
if (savedInstanceState != null) {
return;
}
// Create a new Fragment to be placed in the activity layout
FragmentOne fragmentOne = new FragmentOne ();
// Add the fragment to the 'fragment_container' FrameLayout
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, fragmentOne ).commit();
}
}
此活动最初显示片段一。
片段一个有一个监听的按钮，当它被点击时，它将用片段2替换它自己。单击该按钮时，片段1中的界面
//Main acitivty has this method which is a a method the interface in fragment one requires
@Override
public void goToFragmentTwo() {
//Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
// setSupportActionBar(toolbar);
// Create fragment and give it an argument specifying the article it should show
FragmentTwo fragmentTwo = new FragmentTwo ();
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, fragmentTwo );
transaction.addToBackStack(FragmentTwo.BACKSTACK_TAG);
// Commit the transaction
transaction.commit();
}
如果调用工具栏中的android后退按钮或后退按钮，则片段需要有一个确认对话框，询问您是否确定要离开。如果好，那么我有第二个活动，称为HomeActivity（此活动是MainActivity的父活动），它需要去，或者如果取消它只需要关闭对话框并保留在当前片段中。
所以在MainActivity中我覆盖了onBackPressed方法，它显示了一个：
@覆盖 public void onBackPressed（）{ AlertDialog.Builder builder = new AlertDialog.Builder（this）;
builder.setMessage("Do you want to leave? ");
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
MainActivity.super.onBackPressed();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
finish();
}
});
builder.show();
}
我遇到了这个代码的两个问题：
1）按工具栏中的后退按钮不会显示对话框 2）对话框的“确定”和“取消”功能无法正常工作。
基本上我想要完成的是我有一个HomeActivity，它有一个导航到MainActivity的按钮。当MainActivity被调用时，我将启动一个工作流，其中每个片段都是该工作流的一部分。如果按下后退按钮，则需要丢弃此工作流程，并且应将用户返回到HomeActivty。
答案 0 :(得分：4)
我假设您正在使用ActionBar。
尝试在您的活动中添加此内容：
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
onBackPressed();
return true;
}
return false;
}
@Override
public void onBackPressed() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Do you want to leave? ");
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
MainActivity.super.onBackPressed();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
finish();
}
});
builder.show();
}
答案 1 :(得分：0)
1）你应该让你的工具栏后退按钮从你的活动中调用onBackPressed（），这样它们就可以共享相同的功能。
请参阅主要活动中的onSupportNavegationUp（）。
2）让您的主要活动控制片段发生的事情，但如果必须，请让片段处理任何背压。
我希望这对你有用。
清单
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.johnurrutia.so_43172788">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/Theme.AppCompat.Light.NoActionBar">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
activity_main.xml中
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
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="com.johnurrutia.so_43172788.MainActivity">
<android.support.v7.widget.Toolbar
android:id="@+id/toolBar"
android:layout_width="0dp"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
android:elevation="4dp"
android:theme="@style/ThemeOverlay.AppCompat.ActionBar"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent">
</android.support.v7.widget.Toolbar>
<FrameLayout
android:id="@+id/fragment_container"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintTop_toBottomOf="@id/toolBar"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintBottom_toBottomOf="parent"
tools:layout_editor_absoluteY="8dp">
</FrameLayout>
</android.support.constraint.ConstraintLayout>
fragment_one.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">
<Button
android:id="@+id/btnGoFrag2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Go To Fragment TWO" />
</LinearLayout>
fragment_two.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">
<Button
android:id="@+id/goToFragmentOne"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Go To Fragment One" />
</LinearLayout>
MainActivity.java
public class MainActivity extends AppCompatActivity
implements FragmentOne.OnFragmentOneInteractionListener, FragmentTwo.OnFragmentTwoInteractionListener {
public static final int FRAGMENT_ONE = 0;
public static final int FRAGMENT_TWO = 1;
private Toolbar toolbar;
private FragmentOne fragmentOne;
private FragmentTwo fragmentTwo;
private ArrayList<Fragment> fragments = new ArrayList<>();
private int currentFragment = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = (Toolbar) findViewById(R.id.toolBar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
// Check that the activity is using the layout version with
// the fragment_container FrameLayout
if (findViewById(R.id.fragment_container) != null) {
// However, if we're being restored from a previous state,
// then we don't need to do anything and should return or else
// we could end up with overlapping fragments.
if (savedInstanceState != null) {
return;
}
// Create a new Fragment to be placed in the activity layout
fragmentOne = new FragmentOne();
fragmentTwo = new FragmentTwo();
fragments.add(FRAGMENT_ONE, fragmentOne);
fragments.add(FRAGMENT_TWO, fragmentTwo);
// Add the fragment to the 'fragment_container' FrameLayout
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, fragmentOne,"FRAGMENT_ONE")
.add(R.id.fragment_container, fragmentTwo, "FRAGMENT_TWO")
.hide(fragmentTwo)
.show(fragmentOne)
.commit();
}
}
@Override
public boolean onSupportNavigateUp() {
onBackPressed();
return true;
}
@Override
public void onBackPressed() {
boolean fragmentProcessedTheEvent = ( (BackButtonListener) fragments.get(currentFragment)).onBackPressed();
if(!fragmentProcessedTheEvent) {
//The event is for Main Activity to exit
showActivityExitDialog();
}
}
public void showActivityExitDialog() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Do you want to leave? ");
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
finish();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.dismiss();
}
});
builder.show();
}
private void switchToFragment(int pos) {
if (currentFragment != pos) {
getSupportFragmentManager().beginTransaction()
.hide(fragments.get(currentFragment))
.show(fragments.get(pos))
.commit();
currentFragment = pos;
}
}
public void goToFragmentTwo(){
switchToFragment(FRAGMENT_TWO);
}
public void goToFragmentOne(){
switchToFragment(FRAGMENT_ONE);
}
}
FragmentOne.java
public class FragmentOne extends Fragment implements BackButtonListener{
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_one, container, false);
Button goToFragmentTwoBtn = (Button) v.findViewById(R.id.btnGoFrag2);
goToFragmentTwoBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
( (OnFragmentOneInteractionListener) getActivity() ).goToFragmentTwo();
}
});
return v;
}
public interface OnFragmentOneInteractionListener{
public void goToFragmentTwo();
}
@Override
public boolean onBackPressed() {
/*
* if(fragment_has_any_use_for_back_press){
* process_it_here();
* return EVENT_PROCESSED;
* }
*
* */
return EVENT_IGNORED;
}
}
FragmentTwo.java
public class FragmentTwo extends Fragment implements BackButtonListener{
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_two, container, false);
Button goToFragmentTwoBtn = (Button) v.findViewById(R.id.goToFragmentOne);
goToFragmentTwoBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
( (FragmentTwo.OnFragmentTwoInteractionListener) getActivity() ).goToFragmentOne();
}
});
return v;
}
@Override
public boolean onBackPressed() {
/*
* if(fragment_has_any_use_for_back_press){
* process_it_here();
* return EVENT_PROCESSED;
* }
*
* */
return EVENT_IGNORED;
}
public interface OnFragmentTwoInteractionListener{
public void goToFragmentOne();
}
}
BackButtonListener.java
public interface BackButtonListener {
public static final boolean EVENT_PROCESSED = true;
public static final boolean EVENT_IGNORED = false;
public boolean onBackPressed();
}