Android addToBackStack(null) 不工作，关闭应用程序

Question

在我的应用程序中，我在一个 Activity 中使用 Fragments，我正在尝试替换它们。这很好用，但是在后按时我想切换到上一个片段。我找到了 addToBackStack() 方法，但它不起作用。这是 MainActivity 中的代码：

MainActivity.java：

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Fragment1 fragment1 = new Fragment1();
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(android.R.id.content, fragment1);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();
}

public void changeFragment(Fragment f)
{
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.add(android.R.id.content, f);
    fragmentTransaction.commit();
}

@Override
public void onBackPressed()
{
    if (getSupportFragmentManager().getBackStackEntryCount() > 0 )
    {
        getSupportFragmentManager().popBackStackImmediate();
    }
    else
    {
        super.onBackPressed();
    }
}
}

Fragment1.java：

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

public class Fragment1 extends Fragment
{
private Button buttonFragment1;

public Fragment1() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_fragment1, container, false);
}

@Override
public void onActivityCreated(Bundle savedInstanceState)
{
    super.onActivityCreated(savedInstanceState);
    buttonFragment1 = (Button)getActivity().findViewById(R.id.buttonFragment1);
    buttonFragment1.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            Fragment2 fragment2 = new Fragment2();
            ((MainActivity) getActivity()).changeFragment(fragment2);
        }
    });
}
}

Fragment2.java：

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class Fragment2 extends Fragment {


public Fragment2()
{
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_fragment2, container, false);
}

}

activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.asteam.myapplication.MainActivity">

<fragment
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/fraggment" />
</RelativeLayout>

fragment_fragment1.xml：

<FrameLayout 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="com.example.asteam.myapplication.Fragment1">

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimaryDark">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/buttonFragment1"
        android:text="Send to fragment2"/>

</RelativeLayout>

</FrameLayout>

fragment_fragment2.xml：

<FrameLayout 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="com.example.asteam.myapplication.Fragment2">

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimary">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="Fragment2" />

</RelativeLayout>

</FrameLayout>

和清单 xml：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.asteam.myapplication">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <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>

我试图重写 onBackPressed() 方法：

@Override
public void onBackPressed()
{
    if (getSupportFragmentManager().getBackStackEntryCount() > 0 )
    {
        getSupportFragmentManager().popBackStackImmediate();
    }
    else
    {
        super.onBackPressed();
    }
}

但它不起作用，如果我在单击按钮后显示堆栈号，我会得到 1。我尝试从 android.support.v4. 更改为 android. 到 java 片段文件和主要活动，并将 MainActivity 更改为从 Activity 扩展，但这也不起作用。我究竟做错了什么？我的应用支持 API 14 及更高版本。任何帮助将不胜感激。

已编辑

加上logcat：

02-08 14:38:49.191 10417-10417/? I/art: Not late-enabling -Xcheck:jni (already on)
02-08 14:38:49.266 10417-10417/com.example.asteam.myapplication W/System:  ClassLoader referenced unknown path: /data/app/com.example.asteam.myapplication-2/lib/x86
02-08 14:38:49.322 10417-10432/com.example.asteam.myapplication D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
02-08 14:38:49.452 10417-10432/com.example.asteam.myapplication I/OpenGLRenderer: Initialized EGL, version 1.4
02-08 14:38:49.489 10417-10432/com.example.asteam.myapplication W/EGL_emulation: eglSurfaceAttrib not implemented
02-08 14:38:49.489 10417-10432/com.example.asteam.myapplication W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xabebfe80, error=EGL_SUCCESS
02-08 14:38:55.915 10417-10432/com.example.asteam.myapplication E/Surface: getSlotFromBufferLocked: unknown buffer: 0xab852fc0

Answer 1

像这样改变你的方法

public void changeFragment(Fragment f)
{
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(android.R.id.content, f);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();
}

那么您应该从onCreate 的MainActivity 中删除fragmentTransaction.addToBackStack(null);。

另外，在Fragment1 中的onActivityCreated 中的代码应该移动到onCreateView。