Android-片段之间的导航错误

Question

我目前正在开发具有一个活动和多个片段的应用程序。 片段之间的导航应使用工具栏按钮和后退按钮完成。

但是我遇到了一些错误，我也不知道为什么。

这是MainActivity.java：

package com.geapps.nottaptests.testone;

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (savedInstanceState == null)
        {
            getSupportFragmentManager().beginTransaction().add(R.id.main_container, OneFragment.newInstance(0), "One").commit();
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        if (id == R.id.action_add)
        {
            getSupportFragmentManager().beginTransaction().replace(R.id.main_container, TwoFragment.newInstance(0), "Two").addToBackStack(null).commit();
        }
        return super.onOptionsItemSelected(item);
    }

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

和OneFragment.java：

package com.geapps.nottaptests.testone;

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

public class OneFragment extends Fragment 
{
    public static OneFragment newInstance(int index)
    {
        OneFragment fragment = new OneFragment();

        Bundle args = new Bundle();
        args.putInt("int", index);

        fragment.setArguments(args);

        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View view = inflater.inflate(R.layout.fragment_one, container, false);
        return view;
    }
}

TwoFragment.java完全类似于OneFragment.java。

当我按下TwoFragment.java中的“后退”按钮时，出现以下错误：

Thread [<1> main] (Suspended (exception ClassNotFoundException))    
    <VM does not provide monitor information>   
    PathClassLoader(BaseDexClassLoader).findClass(String) line: 61  
    PathClassLoader(ClassLoader).loadClass(String, boolean) line: 501   
    PathClassLoader(ClassLoader).loadClass(String) line: 461    
    BackStackRecord.getEnterTransition(Fragment, boolean) line: 1056    
    BackStackRecord.configureTransitions(int, BackStackRecord$TransitionState, boolean, SparseArray, SparseArray) line: 1138    
    BackStackRecord.beginTransition(SparseArray, SparseArray, boolean) line: 1029   
    BackStackRecord.popFromBackStack(boolean, BackStackRecord$TransitionState, SparseArray, SparseArray) line: 883  
    FragmentManagerImpl.popBackStackState(Handler, String, int, int) line: 1541 
    FragmentManagerImpl$2.run() line: 493   
    FragmentManagerImpl.execPendingActions() line: 1489 
    FragmentManagerImpl$1.run() line: 454   
    Handler.handleCallback(Message) line: 615   
    FragmentActivity$1(Handler).dispatchMessage(Message) line: 92   
    Looper.loop() line: 137 
    ActivityThread.main(String[]) line: 4921    
    Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]  
    Method.invoke(Object, Object...) line: 511  
    ZygoteInit$MethodAndArgsCaller.run() line: 1038 
    ZygoteInit.main(String[]) line: 805 
    NativeStart.main(String[]) line: not available [native method]  

Answer 1

我通过制作自己的自定义后台堆栈解决了这个问题。 唯一的问题是，我必须注意不要一次添加同一片段。

BackStack.java：

package com.geapps.nottaptests.testone;

import java.util.ArrayList;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;

public class BackStack 
{
    private FragmentManager fragmentManager;
    private ArrayList<Fragment> fragments = new ArrayList<Fragment>();

    public BackStack(FragmentManager fragmentManager)
    {
        this.fragmentManager = fragmentManager;
    }

    public void add(Fragment fragment)
    {
        fragments.add(fragment);
        fragmentManager.beginTransaction().replace(R.id.main_container, this.get()).commit();
    }

    public void pop()
    {
        fragments.remove(fragments.size() - 1);
        fragmentManager.beginTransaction().replace(R.id.main_container, this.get()).commit();
    }

    public Fragment get()
    {
        return fragments.get(fragments.size() - 1);
    }

    public int getNumber()
    {
        return fragments.size();
    }
}

它正在使用中：

BackStack backStack = new BackStack(getSupportFragmentManager());
...
Fragment fragment = OneFragment.newInstance(0);
            backStack.add(fragment);
...
Fragment fragment = TwoFragment.newInstance(0);
            backStack.add(fragment);
...
backStack.pop()