使用操作欄選項卡切換片段

Question

一週後，我仍然試圖創建一個帶有v7支持的選項卡式操作欄，以便能夠在片段之間切換。這是我在本機代碼中的第一個Android應用程序，我是Java新手。

我Main.Activity.java看起來像這樣

package com.example.appcompattest; 

import android.os.Bundle; 
import android.app.Activity; 
import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentTransaction; 
import android.view.Menu; 
import android.support.v7.app.ActionBar; 
import android.support.v7.app.ActionBar.Tab; 
import android.support.v7.app.ActionBarActivity; 


public class MainActivity extends ActionBarActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
    // setup action bar for tabs 
    ActionBar actionBar = getSupportActionBar(); 
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 
    actionBar.setDisplayShowTitleEnabled(true); 

    Tab tab = actionBar.newTab() 
         .setText(R.string.grammar) 
         .setTabListener(new TabListener<GrammarFragment>(
           this, "GRAMMAR", GrammarFragment.class)); 
    actionBar.addTab(tab); 

    tab = actionBar.newTab() 
        .setText(R.string.lexis) 
        .setTabListener(new TabListener<LexisFragment>(
          this, "LEXIS", LexisFragment.class)); 
    actionBar.addTab(tab); 
} 

@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; 
} 


public static class TabListener<T extends Fragment> implements ActionBar.TabListener { 
    private Fragment mFragment; 
    private final Activity mActivity; 
    private final String mTag; 
    private final Class<T> mClass; 

    /** Constructor used each time a new tab is created. 
     * @param activity The host Activity, used to instantiate the fragment 
     * @param tag The identifier tag for the fragment 
     * @param clz The fragment's Class, used to instantiate the fragment 
     */ 

    public TabListener(Activity activity, String tag, Class<T> clz) { 
     mActivity = activity; 
     mTag = tag; 
     mClass = clz; 
    } 

    /* The following are each of the ActionBar.TabListener call backs */ 
    public void onTabSelected(Tab tab, FragmentTransaction ft) { 
     // Check if the fragment is already initialized 
     if (mFragment == null) { 
      // If not, instantiate and add it to the activity 
      mFragment = Fragment.instantiate(mActivity, mClass.getName()); 
      // Commit the transaction 
      ft.add(R.id.fragment_holder, mFragment, mTag); 
     } else { 
      // If it exists, simply attach it in order to show it 
      ft.attach(mFragment); 
     } 
    } 

    public void onTabUnselected(Tab tab, FragmentTransaction ft) { 
     if (mFragment != null) { 
      // Detach the fragment, because another one is being attached 
      ft.detach(mFragment); 
     } 
    } 

    public void onTabReselected(Tab tab, FragmentTransaction ft) { 
     // User selected the already selected tab. Usually do nothing. 
    } 
} 

} 

從這個

除此之外，我有一個FrameLayout裏我activity_main.xml中交換的選項卡進出稱爲fragment_holder，以及單獨的XML文件，我兩個片段。我也有兩個類，LexisFragment.java和GrammarFragment.java，它們基本相同（用語法/文法替代Lexis /詞法）並且看起來像這樣。

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

當我運行該活動時，會添加第一個片段。選擇其他選項卡會導致添加第二個片段，但不會破壞第一個片段。在隨後的選項卡更改中，片段只是保持疊加。

在每個步驟記錄的變量（MTAG和mFragment），並與ft.remove（）試驗後，我敢肯定，正在發生的事情如下： 在第一個選項卡改變onTabUnselected未能分離/刪除任何東西而onTabSelected添加新的片段。然後，在成功更換標籤時，應該添加的標籤被刪除，而應該刪除的標籤被添加。我很感激任何建議。

Answer 1

希望這有助於你..

public class AboutActivity extends Activity { 
boolean mIsFromMem; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    mIsFromMem=savedInstanceState!=null; 
}}