这是我的依赖项：

Question

我正在尝试使用导航图在两个片段之间导航。出于某种原因，当我使用图的生成的动作调用Navigation方法时，目标片段正在“创建”但没有出现，而起始片段只是就好像它已被停用但没有消失一样。我认为我已经按照Google's documentation page for this中列出的所有步骤进行操作，但是我可能缺少一些简单的东西！

这是我的依赖项：

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    // ViewModel and LiveData
    def lifecycle_version = "2.1.0"
    implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"

    def nav_version = "2.1.0"
    implementation "androidx.navigation:navigation-fragment:$nav_version"
    implementation "androidx.navigation:navigation-ui:$nav_version"

    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.2.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

MainActivity

在我的主要活动课程中，我只是在ModelView中定义一个OnCreate()：

public class MainActivity extends AppCompatActivity {
    MealDataModel mealDataModel;

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

        // Create the model on create of the main activity
        mealDataModel = ViewModelProviders.of(this).get(MealDataModel.class);
    }
}

在我的主要活动布局中，我只是使用NavHostFragment：

...
<fragment
        android:id="@+id/fragment2"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/nav_graph" />
...

导航图

这是我的导航图：

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/nav_graph"
    app:startDestination="@id/mealCostFrag">

    <fragment
        android:id="@+id/mealCostFrag"
        android:name="com.finley.program2.frag.MealCostFrag"
        android:label="fragment_meal_cost"
        tools:layout="@layout/fragment_meal_cost" >
        <action
            android:id="@+id/action_mealCostFrag_to_tipPercentFrag"
            app:destination="@id/tipPercentFrag" />
    </fragment>
    <fragment
        android:id="@+id/tipPercentFrag"
        android:name="com.finley.program2.frag.TipPercentFrag"
        android:label="fragment_tip_percent"
        tools:layout="@layout/fragment_tip_percent" />
</navigation>

开始片段

我导航图的开始目标是这个片段...：

public class MealCostFrag extends Fragment {
    private MealDataModel mealDataModel;
    private EditText etCost;
    private Button btnNext;
    private double cost;
    public MealCostFrag() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View myView = inflater.inflate(R.layout.fragment_meal_cost, container, false);
        mealDataModel = ViewModelProviders.of(getActivity()).get(MealDataModel.class);

        // Set listeners and such...
        etCost = myView.findViewById(R.id.editText01);
        btnNext= myView.findViewById(R.id.button01);
        btnNext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    cost = Double.parseDouble(etCost.getText().toString());
                    if (cost <= 0) throw new Exception();
                    mealDataModel.setMealCost(cost);
                    Log.i("COST FRAG","Navigating to tip pct with cost = " + mealDataModel.getMealCost());
                    Navigation.findNavController(v).navigate(R.id.action_mealCostFrag_to_tipPercentFrag);
                } catch (Exception e) {
                    Log.e("COST FRAG", "Invalid cost entered, cost = " + cost);
                    Toast.makeText(getContext(),
                            "Please enter a valid meal cost.", Toast.LENGTH_SHORT).show();
                }
            }
        });
        return myView;

    }

}

采用这种布局：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".frag.MealCostFrag">

    <EditText
        android:id="@+id/editText01"
        android:layout_width="0dp"
        android:layout_height="55dp"
        android:layout_marginStart="64dp"
        android:layout_marginLeft="64dp"
        android:layout_marginTop="48dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:ems="10"
        android:gravity="center_horizontal|center_vertical"
        android:hint="Cost"
        android:inputType="number|numberDecimal"
        android:textSize="24sp"
        app:layout_constraintEnd_toStartOf="@+id/button01"
        app:layout_constraintHorizontal_bias="1.0"/>

    <Button
        android:id="@+id/button01"
        android:layout_width="87dp"
        android:layout_height="46dp"
        android:layout_marginEnd="64dp"
        android:layout_marginRight="64dp"
        android:text="Next"
        app:layout_constraintBaseline_toBaselineOf="@+id/editText01"
        app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

目标片段：

这是我要导航到的片段，它的布局为空：

public class TipPercentFrag extends Fragment {
    private MealDataModel mealDataModel;
    public TipPercentFrag() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View myView = inflater.inflate(R.layout.fragment_meal_cost, container, false);
        mealDataModel = ViewModelProviders.of(getActivity()).get(MealDataModel.class);

        // Set listeners and such...
        Log.i("TIP PCT FRAG", "CreateView of tip pct frag called");

        return myView;

    }
}

我发现与此有关的特殊之处是正在输出目标片段的“ onCreateView（）”方法中的日志，但它并未显示。

我知道我已经为大家提供了大量的代码来进行筛选，因此我对任何愿意花时间帮助我的人都非常感激。我将根据要求提供任何其他必要的信息。预先谢谢大家，希望这是我犯的一个小错误！

Answer 1

就像我怀疑的那样，我犯了一个非常简单的错误。我在目标片段上夸大的视图是我的起始片段的视图。只是复制和粘贴错误。

此：

// Inflate the layout for this fragment
        View myView = inflater.inflate(R.layout.fragment_meal_cost, container, false);
        mealDataModel = ViewModelProviders.of(getActivity()).get(MealDataModel.class);

只需要这样：

// Inflate the layout for this fragment
        View myView = inflater.inflate(R.layout.fragment_tip_percent, container, false);
        mealDataModel = ViewModelProviders.of(getActivity()).get(MealDataModel.class);

在此汲取的教训是在调试时仔细检查过程的每个步骤！错误的确通常隐藏在视线范围内。

Answer 2

如果您使用数据绑定，请更改充气线这些线

来自

mDataBinding=DataBindingUtil.inflate(getLayoutInflater(),R.layout.fragment_date_sheet, container, false);

到

mDataBinding= DataBindingUtil.inflate(inflater,R.layout.fragment_date_sheet, container, false);

导航中未显示Android目标片段

这是我的依赖项：

MainActivity

导航图

开始片段

目标片段：

2 个答案: