局部變量

Question

我有，我想從列表中顯示值的片段，所以我得到像這樣的活動烹飪法詳情

 IngredientsFragment ingredientsFrag = new IngredientsFragment(); 
    ingredientsFrag.setPosition(position); 
    ingredientsFrag.setRecipes(MainActivity.receipes); 
    getSupportFragmentManager().beginTransaction() 
      .replace(R.id.FRGingredients, ingredientsFrag) 
      .commit(); 

那裏的主要事情要注意的是SetRecipes（）方法，我傳遞一個列表，它是MainActivity類中的一個靜態列表。

的成分片段我成分片段有這樣的：

public class IngredientsFragment extends Fragment { 
int position; 
List<Recipe> mRecipes; 
String test; 


@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
    View rootView = inflater.inflate(R.layout.frag_recipe_ingredients, container, false); 
    TextView ingredients = rootView.findViewById(R.id.ingredientsTxt); 

    ingredients.setText(String.valueOf(mRecipes.get(0).getName())); 
    return rootView; 
} 

public void setPosition(int position) { 
    this.position = position; 
} 

public void setRecipes(List<Recipe> recipes) { 
    test = String.valueOf(recipes.get(0).getName()); 
    mRecipes = recipes; 
} 
} 

當我運行這段代碼，這是我所得到的：

11-10 23:14:17.682 2812-2812/com.lemuel.lemubit.bakenow E/AndroidRuntime: FATAL EXCEPTION: main 
     Process: com.lemuel.lemubit.bakenow, PID: 2812 
     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lemuel.lemubit.bakenow/com.lemuel.lemubit.bakenow.RecipeDetail}: android.view.InflateException: Binary XML file line #9: Binary XML file line #9: Error inflating class fragment 
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2583) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2665) 
     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1499) 
     at android.os.Handler.dispatchMessage(Handler.java:111) 
     at android.os.Looper.loop(Looper.java:207) 
     at android.app.ActivityThread.main(ActivityThread.java:5765) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679) 
     Caused by: android.view.InflateException: Binary XML file line #9: Binary XML file line #9: Error inflating class fragment 
                      at android.view.LayoutInflater.inflate(LayoutInflater.java:539) 
     at android.view.LayoutInflater.inflate(LayoutInflater.java:423) 
     at android.view.LayoutInflater.inflate(LayoutInflater.java:374) 
     at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:289) 
     at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139) 
     at com.lemuel.lemubit.bakenow.RecipeDetail.onCreate(RecipeDetail.java:15) 
     at android.app.Activity.performCreate(Activity.java:6360) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1113) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2530) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2665) 
     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1499) 
     at android.os.Handler.dispatchMessage(Handler.java:111) 
     at android.os.Looper.loop(Looper.java:207) 
     at android.app.ActivityThread.main(ActivityThread.java:5765) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679) 
     Caused by: android.view.InflateException: Binary XML file line #9: Error inflating class fragment 
                      at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:782) 
     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704) 
     at android.view.LayoutInflater.rInflate(LayoutInflater.java:835) 
     at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798) 
     at android.view.LayoutInflater.inflate(LayoutInflater.java:515) 
     at android.view.LayoutInflater.inflate(LayoutInflater.java:423) 
     at android.view.LayoutInflater.inflate(LayoutInflater.java:374) 
     at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:289) 
     at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139) 
     at com.lemuel.lemubit.bakenow.RecipeDetail.onCreate(RecipeDetail.java:15) 
     at android.app.Activity.performCreate(Activity.java:6360) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1113) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2530) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2665) 
     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1499) 
     at android.os.Handler.dispatchMessage(Handler.java:111) 
     at android.os.Looper.loop(Looper.java:207) 
     at android.app.ActivityThread.main(ActivityThread.java:5765) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679) 
     Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object java.util.List.get(int)' on a null object reference 
     at com.lemuel.lemubit.bakenow.Fragments.IngredientsFragment.onCreateView(IngredientsFragment.java:34) 
     at android.support.v4.app.Fragment.performCreateView(Fragment.java:2239) 
     at android.support.v4.app.FragmentManagerImpl.ensureInflatedFragmentView(FragmentManager.java:1507) 
     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1303) 
     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1502) 
     at android.support.v4.app.FragmentManagerImpl.addFragment(FragmentManager.java:1737) 
     at android.support.v4.app.FragmentManagerImpl.onCreateView(FragmentManager.java:3512) 
     at android.support.v4.app.FragmentController.onCreateView(FragmentController.java:120) 
     at android.support.v4.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:330) 
     at android.support.v4.app.BaseFragmentActivityApi14.onCreateView(BaseFragmentActivityApi14.java:39) 
     at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:75) 
     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:754) 
     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704) 
     at android.view.LayoutInflater.rInflate(LayoutInflater.java:835) 
     at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798) 
     at android.view.LayoutInflater.inflate(LayoutInflater.java:515) 
     at android.view.LayoutInflater.inflate(LayoutInflater.java:423) 
     at android.view.LayoutInflater.inflate(LayoutInflater.java:374) 
     at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:289) 
     at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139) 
     at com.lemuel.lemubit.bakenow.RecipeDetail.onCreate(RecipeDetail.java:15) 
     at android.app.Activity.performCreate(Activity.java:6360) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1113) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2530) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2665) 
     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1499) 
     at android.os.Handler.dispatchMessage(Handler.java:111) 
     at android.os.Looper.loop(Looper.java:207) 
     at android.app.ActivityThread.main(ActivityThread.java:5765) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679) 

所以它不能識別變量mRecipes，但令我感到困惑的是，當我使用變量測試它炒作時，這意味着該列表實際上被傳遞該方法，但任何時候我嘗試在onCreateView中訪問它，它告訴我，空錯誤。雖然我可以訪問測試如果我將其更改爲

ingredients.setText(test); 

它的工作原理，當我那樣做，這意味着OnCreateView是看到變量測試這也意味着列表傳入方法最初沒有空值。

Answer 1

引起：顯示java.lang.NullPointerException：嘗試在上一個com.lemuel.lemubit空對象引用 調用接口方法 'java.lang.Object中java.util.List.get（INT）'。 bakenow.Fragments.IngredientsFragment.onCreateView（IngredientsFragment.java:34）

異常清晰的NullPointerException在訪問列表。 你必須把你的列表放到Bundle中，並將它設置爲你的片段的參數。然後在片段類中，你可以從onCreateView方法的片段中獲得這個bundle。

Answer 2

這不是你如何將一個數組或任何其他變量傳遞給活動的片段。你必須通過一個捆綁你的陣列到你的片段：

Bundle bundle = new Bundle(); 
bundle.putStringArrayList("edttext", arraylist); 
Fragmentclass fragobj = new Fragmentclass(); 
fragobj.setArguments(bundle); 

IngredientsFragment ingredientsFrag = new IngredientsFragment(); 
ingredientsFrag.setArguments(bundle); 
getSupportFragmentManager().beginTransaction() 
      .replace(R.id.FRGingredients, ingredientsFrag) 
      .commit(); 

確保您的POJO食譜實現Parcelable。