当我单击其他片段中的搜索按钮时，java应用程序崩溃

Question

我的天气应用程序在搜索面板上搜索城市，效果很好。唯一的问题是，如果我单击底部导航视图上的下一个选项卡（小时和每日部分），然后 单击此处的搜索按钮，它显示以下异常：

java.lang.ClassCastException: com.viz.lightweatherforecast.SecondFragment cannot be cast to com.viz.lightweatherforecast.FirstFragment
        at com.viz.lightweatherforecast.Activity.HomeActivity$2.onClick(HomeActivity.java:94)
        at 安卓.view.View.performClick(View.java:7044)
        at 安卓.view.View.performClickInternal(View.java:7017)
        at 安卓.view.View.access$3200(View.java:784)
        at 安卓.view.View$PerformClick.run(View.java:26596)
        at 安卓.os.Handler.handleCallback(Handler.java:873)
        at 安卓.os.Handler.dispatchMessage(Handler.java:99)
        at 安卓.os.Looper.loop(Looper.java:193)
        at 安卓.app.ActivityThread.main(ActivityThread.java:6819)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.安卓.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:497)
        at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:912)

此错误清楚地表明错误来自活动的此行：

FirstFragment firstFragment = (FirstFragment) navHostFragment.getChildFragmentManager().getFragments().get(0);
                firstFragment.getWeatherData(textfield.getText().toString().trim());

因此，我尝试添加以下内容：

SecondFragment secondFragment = (SecondFragment) navHostFragment.getChildFragmentManager().getFragments().get(0);
                secondFragment.getWeatherData(textfield.getText().toString().trim());

所以它可以支持我的第二个片段，但它仍然给出了错误。我也曾在这个网站上搜索过答案，但没有找到任何解决方案

为了进一步解释这个应用程序，我有一个活动，它包含3个片段（Firstfragment、Secondfragment和Thirdfragment）。第一个片段标记为“今天”，第二个片段标记为“每小时”，第三个片段标记为“天气”

我现在不打算使用每小时和每天的标签，直到该应用的更高版本。 我的其他片段目前是空的（没有写代码），我现在只想继续使用today选项卡。 但是修复这个错误是必要的，以防用户点击它

我的目的是确保如果我单击其他选项卡上的搜索按钮，不会出现这样的错误，请帮助

我的活动代码：

public class HomeActivity extends AppCompatActivity {
    // Last update time, click sound, search button, search panel.
    TextView time_field;
    MediaPlayer player;
    ImageView Search;
    EditText textfield;
    // For scheduling background image change(using constraint layout, start counting from dubai, down to statue of liberty.
    ConstraintLayout constraintLayout;
    public static int count=0;
    int[] drawable =new int[]{R.drawable.dubai,R.drawable.central_bank_of_nigeria,R.drawable.eiffel_tower,R.drawable.hong_kong,R.drawable.statue_of_liberty};
    Timer _t;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        // use home activity layout.

        time_field = findViewById(R.id.textView9);
        Search = findViewById(R.id.imageView4);
        textfield = findViewById(R.id.textfield);
        //  find the id's of specific variables.

        BottomNavigationView bottomNavigationView = findViewById(R.id.bottomNavigationView);
        // host 3 fragments along with bottom navigation.
        final NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment);
        assert navHostFragment != null;
        final NavController navController = navHostFragment.getNavController();
        NavigationUI.setupWithNavController(bottomNavigationView, navController);


        // For scheduling background image change
        constraintLayout = findViewById(R.id.layout);
        constraintLayout.setBackgroundResource(R.drawable.dubai);
        _t = new Timer();
        _t.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                // run on ui thread
                runOnUiThread(() -> {
                    if (count < drawable.length) {

                        constraintLayout.setBackgroundResource(drawable[count]);
                        count = (count + 1) % drawable.length;
                    }
                });
            }
        }, 5000, 5000);

        Search.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // make click sound when search button is clicked.
                player = MediaPlayer.create(HomeActivity.this, R.raw.click);
                player.start();

                getWeatherData(textfield.getText().toString().trim());
                // make use of some fragment's data
                FirstFragment firstFragment = (FirstFragment) navHostFragment.getChildFragmentManager().getFragments().get(0);
                firstFragment.getWeatherData(textfield.getText().toString().trim());
            }

            private void getWeatherData(String name) {

                ApiInterface apiInterface = ApiClient.getClient().create(ApiInterface.class);

                Call<Example> call = apiInterface.getWeatherData(name);

                call.enqueue(new Callback<Example>() {
                    @Override
                    public void onResponse(@NonNull Call<Example> call, @NonNull Response<Example> response) {

                        try {
                            assert response.body() != null;
                            time_field.setVisibility(View.VISIBLE);
                            time_field.setText("Last Updated:" + " " + response.body().getDt());
                        } catch (Exception e) {
                            time_field.setVisibility(View.GONE);
                            time_field.setText("Last Updated: Unknown");
                            Log.e("TAG", "No City found");
                            Toast.makeText(HomeActivity.this, "No City found", Toast.LENGTH_SHORT).show();
                        }
                    }

                    @Override
                    public void onFailure(@NotNull Call<Example> call, @NotNull Throwable t) {
                        t.printStackTrace();
                    }

                });
            }

        });
    }
}

活动。xml代码：

<?xml version="1.0" encoding="utf-8"?>
<安卓x.constraintlayout.widget.ConstraintLayout xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
    xmlns:app="http://schemas.安卓.com/apk/res-auto"
    xmlns:tools="http://schemas.安卓.com/tools"
    安卓:layout_width="match_parent"
    安卓:layout_height="match_parent"
    安卓:id="@+id/layout"
    安卓:background="@drawable/dubai"
    tools:context=".Activity.HomeActivity">

    <com.google.安卓.material.bottomnavigation.BottomNavigationView
        安卓:id="@+id/bottomNavigationView"
        安卓:layout_width="wrap_content"
        安卓:layout_height="wrap_content"
        安卓:background="#FFFFFF"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:menu="@menu/bottom_menu" />

    <安卓x.fragment.app.FragmentContainerView
        安卓:id="@+id/fragment"
        安卓:name="安卓x.navigation.fragment.NavHostFragment"
        安卓:layout_width="409dp"
        安卓:layout_height="599dp"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@+id/bottomNavigationView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:navGraph="@navigation/my_nav"
        />

    <EditText
        安卓:id="@+id/textfield"
        安卓:layout_width="250dp"
        安卓:layout_height="35dp"
        安卓:autofillHints="@string/change_city"
        安卓:background="@color/colorPrimary"
        安卓:hint="@string/search_city"
        安卓:inputType="text"
        安卓:labelFor="@id/imageView4"
        安卓:padding="8dp"
        安卓:textColor="@color/colorAccent"
        安卓:textSize="16sp"
        app:layout_constraintEnd_toStartOf="@+id/imageView4"
        app:layout_constraintTop_toTopOf="parent" />

    <ImageView
        安卓:id="@+id/imageView4"
        安卓:layout_width="50dp"
        安卓:layout_height="35dp"
        安卓:layout_marginEnd="1dp"
        安卓:contentDescription="@string/searchbtn"
        安卓:src="@drawable/look"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        安卓:id="@+id/textView9"
        安卓:layout_width="wrap_content"
        安卓:layout_height="wrap_content"
        安卓:text="@string/time_field"
        安卓:visibility="gone"
        安卓:textColor="#FFFFFF"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textfield" />


</安卓x.constraintlayout.widget.ConstraintLayout>

 

Answer 1

要从NavHostFragment获得对所显示片段的正确引用，必须先检查片段类类型，然后再尝试向下转换它

根据你的问题：

App crashes when I click the search button in my other fragments

在其他片段之间切换时，无法始终检索第一个片段或第二个片段实例作为可见片段

因此，只需将代码更改为如下所示：

Fragment currentFragment = (Fragment) navHostFragment.getChildFragmentManager().getFragments().get(0);
if(currentFragment instanceof FirstFragment) {
    FirstFragment firstFragment = (FirstFragment)currentFragment;
    firstFragment.getWeatherData(textfield.getText().toString().trim());
}
else if(currentFragment instanceof SecondFragment) {
    SecondFragment secondFragment = (SecondFragment)currentFragment;
    secondFragment.getWeatherData(textfield.getText().toString().trim());
}
else if(currentFragment instanceof ThirdFragment) {
    ThirdFragment thirdFragment = (ThirdFragment)currentFragment;
    thirdFragment.getWeatherData(textfield.getText().toString().trim());
}