Android topics — 10: כניסה, חזרה ותוצאה בין מסכים

NavHostFragment host = (NavHostFragment) getSupportFragmentManager()
        .findFragmentById(R.id.nav_host);
if (host == null) throw new IllegalStateException("Missing navigation host");
NavController nav = host.getNavController();
binding.upButton.setOnClickListener(v -> nav.navigateUp());
nav.addOnDestinationChangedListener((controller, destination, arguments) ->
        binding.upButton.setVisibility(destination.getId() == R.id.catalogFragment
                ? View.GONE : View.VISIBLE));

package com.example.topics;

/** Tiny local source of truth; screens pass IDs and ask this source for data. */
public final class ItemRepository {
    /**
     * Prevents construction of this static, fixed lab data source.
     */
    private ItemRepository() { }

    /**
     * Looks up the current item name by stable identity.
     *
     * @param id identifier received from navigation
     * @return item name, or null when this ID is unknown
     */
    public static String findName(int id) {
        if (id == 1) return "Compass";
        if (id == 2) return "Notebook";
        return null;
    }
}

package com.example.topics;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.navigation.fragment.NavHostFragment;

import com.example.topics.databinding.FragmentCatalogBinding;

/** Start destination; sends only an item ID to the detail destination. */
public final class CatalogFragment extends Fragment {
    private FragmentCatalogBinding binding;

    /**
     * Creates this Fragment's current View without attaching it twice.
     *
     * @param inflater host-aware layout inflater
     * @param container parent providing layout parameters
     * @param savedInstanceState optional restoration state
     * @return the root whose binding is valid until onDestroyView
     */
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {
        binding = FragmentCatalogBinding.inflate(inflater, container, false);
        return binding.getRoot();
    }

    /**
     * Connects actions and renders this destination after the current View exists.
     *
     * @param view newly created root
     * @param savedInstanceState optional state to restore before displaying results
     */
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        binding.openFirst.setOnClickListener(v -> open(1));
        binding.openSecond.setOnClickListener(v -> open(2));
    }

    /**
     * Navigates from the catalog with a stable identity, not a copied item object.
     *
     * @param id identifier to place in the declared itemId argument
     */
    private void open(int id) {
        Bundle args = new Bundle();
        args.putInt("itemId", id);
        NavHostFragment.findNavController(this).navigate(R.id.action_catalog_to_detail, args);
    }

    /**
     * Releases the obsolete View binding while navigation state may remain alive.
     */
    @Override
    public void onDestroyView() {
        binding = null;
        super.onDestroyView();
    }
}

package com.example.topics;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.activity.result.ActivityResultLauncher;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import com.example.topics.databinding.FragmentDetailBinding;

/** Resolves the destination argument from the source and keeps the result as view state. */
public final class DetailFragment extends Fragment {
    private static final String SAVED_COLOR = "selectedColor";
    private FragmentDetailBinding binding;
    private String selectedColor;
    private final ActivityResultLauncher<Void> pickColor =
            registerForActivityResult(new PickColorContract(), color -> {
                if (color != null) {
                    // The result belongs to state even when there is no current View.
                    selectedColor = color;
                    showColor();
                }
            });

    /**
     * Creates this Fragment's current View without attaching it twice.
     *
     * @param inflater host-aware layout inflater
     * @param container parent providing layout parameters
     * @param savedInstanceState optional restoration state
     * @return the root whose binding is valid until onDestroyView
     */
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {
        binding = FragmentDetailBinding.inflate(inflater, container, false);
        return binding.getRoot();
    }

    /**
     * Connects actions and renders this destination after the current View exists.
     *
     * @param view newly created root
     * @param savedInstanceState optional state to restore before displaying results
     */
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        int itemId = requireArguments().getInt("itemId");
        String name = ItemRepository.findName(itemId);
        binding.itemName.setText(name == null
                ? getString(R.string.missing_item, itemId)
                : getString(R.string.item_name, itemId, name));
        if (savedInstanceState != null) {
            selectedColor = savedInstanceState.getString(SAVED_COLOR);
        }
        showColor();
        binding.pickColor.setOnClickListener(v -> pickColor.launch(null));
    }

    /**
     * Renders saved selection only when this Fragment currently owns a View.
     */
    private void showColor() {
        if (binding != null) {
            binding.colorResult.setText(selectedColor == null
                    ? getString(R.string.color_none)
                    : getString(R.string.color_selected, selectedColor));
        }
    }

    /**
     * Copies the color selection for a newly restored Fragment instance.
     *
     * @param outState destination for the small selection snapshot
     */
    @Override
    public void onSaveInstanceState(@NonNull Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString(SAVED_COLOR, selectedColor);
    }

    /**
     * Releases the obsolete View binding while navigation state may remain alive.
     */
    @Override
    public void onDestroyView() {
        binding = null;
        super.onDestroyView();
    }
}

package com.example.topics;

import android.content.Intent;
import android.os.Bundle;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

import com.example.topics.databinding.ActivityPickColorBinding;

/** Small result-producing Activity; Back returns RESULT_CANCELED automatically. */
public final class PickColorActivity extends AppCompatActivity {
    private ActivityPickColorBinding binding;

    /**
     * Creates the new picker screen and connects explicit color-result actions.
     *
     * @param savedInstanceState optional Android restoration snapshot
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        binding = ActivityPickColorBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());
        ViewCompat.setOnApplyWindowInsetsListener(binding.getRoot(), (v, insets) -> {
            Insets bars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
            v.setPadding(bars.left, bars.top, bars.right, bars.bottom);
            return insets;
        });
        binding.chooseRed.setOnClickListener(v -> finishWithColor(getString(R.string.color_red)));
        binding.chooseBlue.setOnClickListener(v -> finishWithColor(getString(R.string.color_blue)));
    }

    /**
     * Sets a successful result before closing the picker.
     *
     * @param color selected name encoded in the contract's result Intent
     */
    private void finishWithColor(String color) {
        setResult(RESULT_OK, new Intent().putExtra(PickColorContract.EXTRA_COLOR, color));
        finish();
    }
}

package com.example.topics;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;

import androidx.activity.result.contract.ActivityResultContract;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

/** Converts an Activity result Intent to a nullable color name. */
public final class PickColorContract extends ActivityResultContract<Void, String> {
    public static final String EXTRA_COLOR = "com.example.topics.COLOR";

    /**
     * Encodes a picker request as an explicit Intent to our internal Activity.
     *
     * @param context context used to construct the Intent
     * @param input unused; this contract takes no input
     * @return Intent for PickColorActivity
     */
    @NonNull
    @Override
    public Intent createIntent(@NonNull Context context, Void input) {
        return new Intent(context, PickColorActivity.class);
    }

    /**
     * Decodes only a successful picker response; cancellation leaves state unchanged.
     *
     * @param resultCode Activity success or cancellation code
     * @param intent optional returned payload
     * @return chosen color, or null for cancellation or missing data
     */
    @Nullable
    @Override
    public String parseResult(int resultCode, @Nullable Intent intent) {
        if (resultCode != Activity.RESULT_OK || intent == null) return null;
        return intent.getStringExtra(EXTRA_COLOR);
    }
}

private final ActivityResultLauncher<Void> pickColor =
        registerForActivityResult(new PickColorContract(), color -> {
            if (color != null) {
                // Keep the result as state even if this Fragment has no current View.
                selectedColor = color;
                showColor();
            }
        });

// In onViewCreated:
binding.pickColor.setOnClickListener(v -> pickColor.launch(null));

package com.example.topics;

import android.content.Intent;
import android.net.Uri;

import androidx.test.core.app.ActivityScenario;
import androidx.test.ext.junit.runners.AndroidJUnit4;
import androidx.test.platform.app.InstrumentationRegistry;

import org.junit.Test;
import org.junit.runner.RunWith;

import static androidx.test.espresso.Espresso.onView;
import static androidx.test.espresso.Espresso.pressBack;
import static androidx.test.espresso.action.ViewActions.click;
import static androidx.test.espresso.assertion.ViewAssertions.matches;
import static androidx.test.espresso.matcher.ViewMatchers.withId;
import static androidx.test.espresso.matcher.ViewMatchers.withText;

/** Observes a graph destination, a typed result, Back/Up, and a deep link. */
@RunWith(AndroidJUnit4.class)
public final class NavigationFlowTest {
    /**
     * Checks typed selection, restoration, and Up to the hierarchical catalog destination.
     */
    @Test
    public void itemResultSurvivesRotationAndUpReturnsToCatalog() {
        try (ActivityScenario<MainActivity> scenario = ActivityScenario.launch(MainActivity.class)) {
            onView(withId(R.id.open_first)).perform(click());
            onView(withId(R.id.item_name)).check(matches(withText("Item 1: Compass")));
            onView(withId(R.id.pick_color)).perform(click());
            onView(withId(R.id.choose_blue)).perform(click());
            onView(withId(R.id.color_result)).check(matches(withText("Selected color: Blue")));
            scenario.recreate();
            onView(withId(R.id.color_result)).check(matches(withText("Selected color: Blue")));
            onView(withId(R.id.up_button)).perform(click());
            onView(withId(R.id.open_second)).check(matches(withText(R.string.open_second)));
        }
    }

    /**
     * Checks the system Back action removes the current detail destination.
     */
    @Test
    public void backPopsOneDestination() {
        try (ActivityScenario<MainActivity> ignored = ActivityScenario.launch(MainActivity.class)) {
            onView(withId(R.id.open_second)).perform(click());
            pressBack();
            onView(withId(R.id.open_first)).check(matches(withText(R.string.open_first)));
        }
    }

    /**
     * Checks an external entry identifies item 2 without first clicking its catalog button.
     */
    @Test
    public void deepLinkLoadsItemById() {
        Intent link = new Intent(Intent.ACTION_VIEW, Uri.parse("topics://item/2"));
        link.setPackage(InstrumentationRegistry.getInstrumentation().getTargetContext().getPackageName());
        try (ActivityScenario<MainActivity> ignored = ActivityScenario.launch(link)) {
            onView(withId(R.id.item_name)).check(matches(withText("Item 2: Notebook")));
            onView(withId(R.id.up_button)).perform(click());
            onView(withId(R.id.open_first)).check(matches(withText(R.string.open_first)));
        }
    }
}