片段类中的局部变量答案

【问题标题】：Local Variable in Fragment class [duplicate]片段类中的局部变量
【发布时间】：2017-11-10 22:28:18
【问题描述】：

我有一个片段，我想在其中显示列表中的值，所以我在 Activity Recipe Detail

中得到它

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

需要注意的主要是 SetRecipes() 方法，我传入了一个 List，它是 MainActivity 类中的一个静态 List。

在成分片段中，我在成分片段中有这个：

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;
}
}

当我运行这段代码时，我得到了：

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)

所以它无法识别变量mRecipes，但让我感到困惑的是，当我使用变量test时它会工作，这意味着列表实际上是向下传递的在该方法中，但每当我尝试在 onCreateView 中访问它时，它都会告诉我那个空错误。虽然我可以访问 test 如果我将其更改为

ingredients.setText(test);

当我这样做时它可以工作，这意味着 OnCreateView 看到变量 test 这也意味着传递给方法的 List 最初不是 null。

【问题讨论】：

标签： android list android-fragments fragment-oncreateview

【解决方案1】：

这不是您将数组或任何其他变量传递给活动片段的方式。您必须将包含数组的捆绑包传递给您的片段：

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();

确保您的 POJO 配方实现 Parcelable。

【讨论】：

【解决方案2】：

原因：java.lang.NullPointerException：尝试在空对象引用上调用接口方法“java.lang.Object java.util.List.get(int)” 在 com.lemuel.lemubit.bakenow.Fragments.IngredientsFragment.onCreateView(IngredientsFragment.java:34)

访问列表时清除 NullPointerException 异常。您必须将列表放入 Bundle 并将其设置为片段的参数.. 然后在片段类中，您可以从 onCreateView 方法中的片段中获取此捆绑包。

【讨论】：