Android - 片段之間的導航錯誤

Question

我目前正在研究一個具有一個活動和多個片段的應用程序。片段之間的導航應該使用工具欄按鈕和後退按鈕完成。

但我收到一些錯誤，我不知道爲什麼。

這裏是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(); 
     } 
    } 
} 

而且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酷似OneFragment.java。

我收到以下錯誤，當我按下TwoFragment.java後退按鈕：

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

我通過使自己的自定義回堆棧解決了這個問題。唯一的問題是我必須小心，不要多次添加相同的片段。

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(); 
    } 
} 

這裏，它是在使用中：

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