RecyclerView - 交替佈局

我很新，對此忍無可忍。這是我的一個簡單的RecyclerView的代碼。我想在LayoutManager中交替使用StaggeredGridLayout和LinearLayout。RecyclerView - 交替佈局

我是如何啓動這兩種佈局的。

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

    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view); 
    recyclerView.setHasFixedSize(true); 

    staggeredGrid = new StaggeredGridLayoutManager(2, 1); 
    cardView = new LinearLayoutManager(this); 
    recyclerView.setLayoutManager(staggeredGrid); 

    List<ItemObjects> staggeredList = getListItemData(); 

    RecyclerViewAdapter adapter = new RecyclerViewAdapter(MainActivity.this, staggeredList); 
    recyclerView.setAdapter(adapter); 
}

我如何嘗試用一個簡單的按鈕在它們之間進行切換。我不知道是否所有代碼都是必需的，但我被告知，每次切換視圖並重新構建適配器時，我都會更好地清除/清空適配器。

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    int id = item.getItemId(); 

    if (id == R.id.view_settings) { 
     if (recyclerView.getLayoutManager() == staggeredGrid) { 
      recyclerView.setAdapter(null); 
      recyclerView.setLayoutManager(cardView); 
      recyclerView.setAdapter(adapter); 
      return true; 
     } 

     if (recyclerView.getLayoutManager() == cardView) { 
      recyclerView.setAdapter(null); 
      recyclerView.setLayoutManager(staggeredGrid); 
      recyclerView.setAdapter(adapter); 
      return true; 
     } 

    } 

    return super.onOptionsItemSelected(item); 
}

和錯誤。

09-06 22:17:37.769 11853-11853/com.example.wsdw E/AndroidRuntime: FATAL EXCEPTION: main 
                   Process: com.example.wsdw, PID: 11853 
                   java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v7.widget.RecyclerView$LayoutManager android.support.v7.widget.RecyclerView.getLayoutManager()' on a null object reference 
                    at com.example.wsdw.MainActivity.onOptionsItemSelected(MainActivity.java:50) 
                    at android.app.Activity.onMenuItemSelected(Activity.java:2908) 
                    at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:406) 
                    at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:195) 
                    at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:103) 
                    at android.support.v7.app.AppCompatDelegateImplV9.onMenuItemSelected(AppCompatDelegateImplV9.java:667) 
                    at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:810) 
                    at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152) 
                    at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:957) 
                    at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:947) 
                    at android.support.v7.widget.ActionMenuView.invokeItem(ActionMenuView.java:616) 
                    at android.support.v7.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:153) 
                    at android.view.View.performClick(View.java:5198) 
                    at android.view.View$PerformClick.run(View.java:21147) 
                    at android.os.Handler.handleCallback(Handler.java:739) 
                    at android.os.Handler.dispatchMessage(Handler.java:95) 
                    at android.os.Looper.loop(Looper.java:148) 
                    at android.app.ActivityThread.main(ActivityThread.java:5417) 
                    at java.lang.reflect.Method.invoke(Native Method) 
                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

我可以做這完全錯了所有我知道，但我正在尋找一個起點，如果有人可以幫幫忙。謝謝，麻煩您了。

來源

2016-09-07 user1754499

你在'的onCreate（）'方法聲明'RecyclerView recyclerView'，所以recyclerView'你想在'onOptionsItemSelected使用它的不一樣'（）'。在'onCreate（）'。'中從該行的開頭刪除'RecyclerView'。 –

感謝邁克，這對我有很大的幫助。從那裏刪除RecyclerView和適配器初始化。在添加notifyDataSetChanged的同時，還遵循了下面發佈的答案，因爲我知道這非常重要。問題：將「Private RecyclerView recyclerView;」放到代碼中是否有效？和「Private RecyclerViewAdapter適配器」;在主類而不是onCreate類？ – user1754499

對於那些使用字段（私有變量）的字段稍微有效一些，所以你不必額外調用像'findViewById（）' - 每次在'Activity'中需要它們。如果你只需要訪問單個方法中的對象，那麼你可以在該方法中聲明它，但顯然需要在多個地方使用它們。 –

RecyclerView recyclerView; 
//Your Activity Name 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    recyclerView = (RecyclerView) findViewById(R.id.recycler_view); 
    recyclerView.setHasFixedSize(true); 

    staggeredGrid = new StaggeredGridLayoutManager(2, 1); 
    cardView = new LinearLayoutManager(this); 
    recyclerView.setLayoutManager(staggeredGrid); 

    List<ItemObjects> staggeredList = getListItemData(); 

    RecyclerViewAdapter adapter = new RecyclerViewAdapter(MainActivity.this, staggeredList); 
    recyclerView.setAdapter(adapter); 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    int id = item.getItemId(); 

    if (id == R.id.view_settings) { 
     if (recyclerView.getLayoutManager() == staggeredGrid) { 
      recyclerView.setAdapter(null); 
      recyclerView.setLayoutManager(cardView); 
      recyclerView.setAdapter(adapter); 
      adapter. notifyDataSetChanged(); 
      return true; 
     } 

     if (recyclerView.getLayoutManager() == cardView) { 
      recyclerView.setAdapter(null); 
      recyclerView.setLayoutManager(staggeredGrid); 
      recyclerView.setAdapter(adapter); 
      adapter. notifyDataSetChanged(); 
      return true; 
     } 

    } 

    return super.onOptionsItemSelected(item); 
}

來源

2016-09-07 03:47:20

RecyclerView - 交替佈局

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