Полное руководство по подключению Android к веб-API ASP.NET Core

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using Microsoft.EntityFrameworkCore;

namespace BlogsApi.Entities

{

    public class BlogsDbContext : DbContext

    {

        public DbSet<Blog> Blogs { get; set; }

        public DbSet<Category> Categories { get; set; }

        public BlogsDbContext(DbContextOptions<BlogsDbContext> options) : base(options)

        {

        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)

        {

            modelBuilder.Entity<Blog>().ToTable("Blog");

            modelBuilder.Entity<Category>().ToTable("Category");

            modelBuilder.Entity<Blog>().HasMany(s => s.Categories).WithMany(c => c.Blogs);

        }

    }

}

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services.AddDbContext<BlogsDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("BlogsDbConnectionString")));

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{

  "ConnectionStrings": {

    "BlogsDbConnectionString": "Server=Home\\SQLEXPRESS;Database=BlogsDb;Trusted_Connection=True;MultipleActiveResultSets=true"

  },

  "Logging": {

    "LogLevel": {

      "Default": "Information",

      "Microsoft": "Warning",

      "Microsoft.Hosting.Lifetime": "Information"

    }

  },

  "AllowedHosts": "*"

}

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using BlogsApi.Entities;

using System.Collections.Generic;

using System.Threading.Tasks;

namespace BlogsApi.Interfaces

{

    public interface IBlogService

    {

        Task<List<Blog>> GetAllBlogs();

        Task<List<Blog>> GetBlogsUnderCategory(int id);

    }

}

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using BlogsApi.Entities;

using System.Collections.Generic;

using System.Threading.Tasks;

namespace BlogsApi.Interfaces

{

    public interface IBlogService

    {

        Task<List<Blog>> GetAllBlogs();

        Task<List<Blog>> GetBlogsUnderCategory(int id);

    }

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using BlogsApi.Entities;

using BlogsApi.Interfaces;

using Microsoft.EntityFrameworkCore;

using System.Collections.Generic;

using System.Linq;

using System.Threading.Tasks;

namespace BlogsApi.Services

{

    public class BlogService : IBlogService

    {

        private readonly BlogsDbContext blogsDbContext;

        public BlogService(BlogsDbContext blogsDbContext)

        {

            this.blogsDbContext = blogsDbContext;

        }

        public async Task<List<Blog>> GetAllBlogs()

        {

            var blogs = blogsDbContext.Blogs.Include(o => o.Categories).Where(o => o.Active).OrderByDescending(o => o.TS);

            return await blogs.ToListAsync();

        }

        public async Task<List<Blog>> GetBlogsUnderCategory(int id)

        {

            var blogs = blogsDbContext.Blogs.Include(o => o.Categories).Where(o => o.Active && o.Categories.Any(category => category.Id == id));

            return await blogs.ToListAsync();

        }

    }

}

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using BlogsApi.Entities;

using BlogsApi.Interfaces;

using Microsoft.EntityFrameworkCore;

using System.Collections.Generic;

using System.Threading.Tasks;

namespace BlogsApi.Services

{

    public class CategoryService : ICategoryService

    {

        private BlogsDbContext blogsDbContext;

        public CategoryService(BlogsDbContext blogsDbContext)

        {

            this.blogsDbContext = blogsDbContext;

        }

        public async Task<List<Category>> GetCategories()

        {

            var categories = blogsDbContext.Categories;

             return await categories.ToListAsync();

        }

    }

}

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services.AddScoped<IBlogService, BlogService>();

services.AddScoped<ICategoryService, CategoryService>();

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using System;

using System.Collections.Generic;

namespace BlogsApi.Models

{

    public class BlogModel

    {

        public int Id { get; set; }

        public string Name { get; set; }

        public string Description { get; set; }

        public string Url { get; set; }

        public string RssFeed { get; set; }

        public DateTime SubmittedDate { get; set; }

        public List<CategoryModel> Categories { get; set; }

    }

}

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namespace BlogsApi.Models

{

    public class CategoryModel

    {

        public int Id { get; set; }

        public string Name { get; set; }

    }

}

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using BlogsApi.Entities;

using BlogsApi.Models;

using System.Collections.Generic;

using System.Linq;

namespace BlogsApi

{

    public class BlogHelper

    {

        public static List<BlogModel> ConvertBlogs(List<Blog> blogs)

        {

            var blogModels = blogs.ConvertAll(blog => new BlogModel

            {

                Id = blog.Id,

                Name = blog.Name,

                Description = blog.Description,

                Url = blog.Url,

                RssFeed = blog.RssFeed,

                SubmittedDate = blog.TS,

                Categories = blog.Categories.ToList().ConvertAll(category => new CategoryModel { Id = category.Id, Name = category.Name })

            });

            return blogModels;

        }

    }

}

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using BlogsApi.Entities;

using BlogsApi.Models;

using System.Collections.Generic;

namespace BlogsApi.Helpers

{

    public class CategoryHelper

    {

        public static List<CategoryModel> ConvertCategories(List<Category> categories)

        {

            var categoryModels = categories.ConvertAll(category => new CategoryModel

            {

                Id = category.Id,

                Name = category.Name,

            });

            return categoryModels;

        }

    }

}

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using BlogsApi.Interfaces;

using Microsoft.AspNetCore.Mvc;

using System.Threading.Tasks;

namespace BlogsApi.Controllers

{

    [ApiController]

    [Route("[controller]")]

    public class BlogsController : ControllerBase

    {

        private readonly IBlogService blogService;

        public BlogsController(IBlogService blogService)

        {

            this.blogService = blogService;

        }

        [HttpGet]

        [Route("")]

        public async Task<IActionResult> Get()

        {

            var blogs = await blogService.GetAllBlogs();

            var blogModels = BlogHelper.ConvertBlogs(blogs);

            return Ok(blogModels);

        }

    }

}

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using BlogsApi.Helpers;

using BlogsApi.Interfaces;

using Microsoft.AspNetCore.Mvc;

using System.Threading.Tasks;

namespace BlogsApi.Controllers

{

    [ApiController]

    [Route("[controller]")]

    public class CategoriesController : ControllerBase

    {

        private readonly ICategoryService categoryService;

        private readonly IBlogService blogService;

        public CategoriesController(ICategoryService categoryService, IBlogService blogService)

        {

            this.categoryService = categoryService;

            this.blogService = blogService;

        }

        [HttpGet]

        [Route("")]

        public async Task<IActionResult> Get()

        {

            var categories = await categoryService.GetCategories();

            var categoryModels = CategoryHelper.ConvertCategories(categories);

            return Ok(categoryModels);

        }

        [HttpGet]

        [Route("{categoryId}/blogs")]

        public async Task<IActionResult> GetCategoryBlogs(int categoryId)

        {

            var blogs = await blogService.GetBlogsUnderCategory(categoryId);

            var blogModels = BlogHelper.ConvertBlogs(blogs);

            return Ok(blogModels);

        }

    }

}

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implementation 'com.squareup.retrofit2:retrofit:2.9.0'

implementation 'com.squareup.retrofit2:converter-gson:2.9.0'

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package com.example.blogs.data.model;

public class Blog {

    private final int Id;

    private final String name;

    private final String description;

    private final String url;

    private final String rssFeed;

    private final String submittedDate;

    public Blog(int id, String name, String description, String url, String rssFeed, String submittedDate) {

        Id = id;

        this.name = name;

        this.description = description;

        this.url = url;

        this.rssFeed = rssFeed;

        this.submittedDate = submittedDate;

    }

    public int getId() {

        return Id;

    }

    public String getName() {

        return name;

    }

    public String getDescription() {

        return description;

    }

    public String getUrl() {

        return url;

    }

    public String getRssFeed() {

        return rssFeed;

    }

    public String getSubmittedDate() {

        return submittedDate;

    }

}

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package com.example.blogs.data.model;

public class Category {

    private final int id;

    private final String name;

    public Category(int id, String name) {

        this.id = id;

        this.name = name;

    }

    public int getId() {

        return id;

    }

    public String getName() {

        return name;

    }

}

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package com.example.blogs.data.remote;

import com.example.blogs.data.model.Blog;

import com.example.blogs.data.model.Category;

import java.util.List;

import retrofit2.Call;

import retrofit2.http.GET;

import retrofit2.http.Path;

public interface IBlogsApi {

    @GET("categories")

    Call<List<Category>> getCategories();

    @GET("categories/{id}/blogs")

    Call<List<Blog>> getBlogsByCategory(@Path("id") int id);

    @GET("blogs")

    Call<List<Blog>> getBlogs();

}

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package com.example.blogs.data.remote;

import retrofit2.Retrofit;

import retrofit2.converter.gson.GsonConverterFactory;

public class RetrofitService {

    public static IBlogsApi Create(){

        Retrofit retrofit = new Retrofit.Builder()

                .baseUrl("http://10.0.2.2:5000/")

                .addConverterFactory(GsonConverterFactory.create())

                .build();

         return retrofit.create(IBlogsApi.class);

    }

}

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package com.example.blogs;

import android.app.Application;

import com.example.blogs.data.remote.BlogsApiManager;

public class MainApplication extends Application {

    public static BlogsApiManager blogsApiManager;

    @Override

    public void onCreate() {

        super.onCreate();

        blogsApiManager = BlogsApiManager.getInstance();

    }

}

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package com.example.blogs.data.remote;

import com.example.blogs.data.model.Blog;

import com.example.blogs.data.model.Category;

import java.util.List;

import retrofit2.Call;

import retrofit2.Callback;

public class BlogsApiManager {

    private static IBlogsApi service;

    private static BlogsApiManager apiManager;

    private BlogsApiManager() {

        service = RetrofitService.Create();

    }

    public static BlogsApiManager getInstance() {

        if (apiManager == null) {

            apiManager = new BlogsApiManager();

        }

        return apiManager;

    }

    public void getCategories(Callback<List<Category>> callback){

        Call<List<Category>> categoriesCall = service.getCategories();

        categoriesCall.enqueue(callback);

    }

    public void getBlogsByCategory(int id, Callback<List<Blog>> callback){

        Call<List<Blog>> blogsByCategoryCall = service.getBlogsByCategory(id);

        blogsByCategoryCall.enqueue(callback);

    }

    public void getBlogs(Callback<List<Blog>> callback){

        Call<List<Blog>> blogsCall = service.getBlogs();

        blogsCall.enqueue(callback);

    }

}

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package com.example.blogs.data.repository;

import androidx.lifecycle.MutableLiveData;

import com.example.blogs.data.model.Blog;

import com.example.blogs.data.remote.BlogsApiManager;

import com.example.blogs.data.model.Category;

import java.util.List;

import retrofit2.Call;

import retrofit2.Callback;

import retrofit2.Response;

public class BlogsRepository {

    private static volatile BlogsRepository instance;

    private final BlogsApiManager blogsApiManager;

    private final MutableLiveData<List<Category>> categories = new MutableLiveData<>();

    private final MutableLiveData<List<Blog>> blogsByCategory = new MutableLiveData<>();

    private final MutableLiveData<List<Blog>> blogs = new MutableLiveData<>();

    private BlogsRepository(BlogsApiManager blogsApiManager) {

        this.blogsApiManager = blogsApiManager;

    }

    public static BlogsRepository getInstance(BlogsApiManager blogsApiManager) {

        if (instance == null) {

            instance = new BlogsRepository(blogsApiManager);

        }

        return instance;

    }

    public MutableLiveData<List<Category>> getCategories(){

        blogsApiManager.getCategories(new Callback<List<Category>>() {

            @Override

            public void onResponse(Call<List<Category>> call, Response<List<Category>> response) {

                if (response.isSuccessful()){

                    List<Category> body = response.body();

                    categories.setValue(body);

                } else{

                    categories.postValue(null);

                }

            }

            @Override

            public void onFailure(Call<List<Category>> call, Throwable t) {

                categories.postValue(null);

            }

        });

        return categories;

    }

    public MutableLiveData<List<Blog>> getBlogsByCategory(int id){

        blogsApiManager.getBlogsByCategory(id, new Callback<List<Blog>>() {

            @Override

            public void onResponse(Call<List<Blog>> call, Response<List<Blog>> response) {

                if (response.isSuccessful()){

                    List<Blog> body = response.body();

                    blogsByCategory.setValue(body);

                } else{

                    blogsByCategory.postValue(null);

                }

            }

            @Override

            public void onFailure(Call<List<Blog>> call, Throwable t) {

                blogsByCategory.postValue(null);

            }

        });

        return blogsByCategory;

    }

    public MutableLiveData<List<Blog>> getBlogs(){

        blogsApiManager.getBlogs(new Callback<List<Blog>>() {

            @Override

            public void onResponse(Call<List<Blog>> call, Response<List<Blog>> response) {

                if (response.isSuccessful()){

                    List<Blog> body = response.body();

                    blogs.setValue(body);

                } else{

                    blogs.postValue(null);

                }

            }

            @Override

            public void onFailure(Call<List<Blog>> call, Throwable t) {

                blogs.postValue(null);

            }

        });

        return blogs;

    }

}

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package com.example.blogs.ui;

import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;

import androidx.navigation.NavController;

import androidx.navigation.Navigation;

import androidx.navigation.ui.AppBarConfiguration;

import androidx.navigation.ui.NavigationUI;

import com.example.blogs.R;

import com.google.android.material.bottomnavigation.BottomNavigationView;

public class MainActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        BottomNavigationView navView = findViewById(R.id.nav_view);

        // Passing each menu ID as a set of Ids because each

        // menu should be considered as top level destinations.

        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(

                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications)

                .build();

        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);

        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);

        NavigationUI.setupWithNavController(navView, navController);

    }

}

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package com.example.blogs.ui.categories;

import androidx.lifecycle.MutableLiveData;

import androidx.lifecycle.ViewModel;

import com.example.blogs.data.model.Category;

import com.example.blogs.data.repository.BlogsRepository;

import java.util.List;

public class CategoriesViewModel extends ViewModel {

    private final BlogsRepository categoryRepository;

    public CategoriesViewModel(BlogsRepository categoryRepository) {

        this.categoryRepository = categoryRepository;

    }

    public MutableLiveData<List<Category>> getCategories() {

        return categoryRepository.getCategories();

    }

}

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package com.example.blogs.ui.categories;

import androidx.annotation.NonNull;

import androidx.lifecycle.ViewModel;

import androidx.lifecycle.ViewModelProvider;

import com.example.blogs.MainApplication;

import com.example.blogs.data.repository.BlogsRepository;

public class CategoriesViewModelFactory implements ViewModelProvider.Factory {

    @NonNull

    @Override

    @SuppressWarnings("unchecked")

    public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {

        if (modelClass.isAssignableFrom(CategoriesViewModel.class)) {

            return (T) new CategoriesViewModel(BlogsRepository.getInstance(MainApplication.blogsApiManager));

        } else {

            throw new IllegalArgumentException("Unknown ViewModel class");

        }

    }

}

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<?xml version="1.0" encoding="utf-8"?>

<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:cardView="http://schemas.android.com/apk/res-auto"

    android:id="@+id/carView"

    android:layout_width="match_parent"

    android:layout_height="100dp"

    cardView:cardCornerRadius="5dp"

    cardView:cardElevation="5dp"

    android:layout_margin="5dp">

    <TextView

        android:id="@+id/category_name"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:padding="14dp"

        android:text="Sample"

        android:textAppearance="@style/Base.TextAppearance.AppCompat.Large" />

</androidx.cardview.widget.CardView>

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package com.example.blogs.ui.categories;

import android.content.Context;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.TextView;

import androidx.annotation.NonNull;

import androidx.recyclerview.widget.RecyclerView;

import com.example.blogs.R;

import com.example.blogs.data.model.Category;

import com.example.blogs.ui.common.OnItemClickListener;

import java.util.ArrayList;

import java.util.List;

public class CategoriesAdapter extends RecyclerView.Adapter<CategoriesAdapter.CategoryViewHolder> {

    @NonNull

    private final Context context;

    private List<Category> categories = new ArrayList<>();

    private final OnItemClickListener<Category> onCategoryClickListener;

    public CategoriesAdapter(@NonNull Context context, OnItemClickListener<Category> onCategoryClickListener) {

        this.context = context;

        this.onCategoryClickListener = onCategoryClickListener;

    }

    @Override

    public CategoryViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        return new CategoryViewHolder(LayoutInflater.from(context).inflate(R.layout.category_item, parent, false));

    }

    @Override

    public void onBindViewHolder(CategoryViewHolder holder, int position) {

        holder.setCategoryItem(categories.get(position));

    }

    @Override

    public int getItemCount() {

        return categories == null ? 0 : categories.size();

    }

    public void setCategories(List<Category> categories) {

        this.categories = categories;

        this.notifyDataSetChanged();

    }

    class CategoryViewHolder extends RecyclerView.ViewHolder {

        private final TextView categoryName;

        private final View categoryItem;

        CategoryViewHolder(View categoryItem) {

            super(categoryItem);

            categoryName = categoryItem.findViewById(R.id.category_name);

            this.categoryItem = categoryItem;

        }

        private void setCategoryItem(Category category){

            categoryName.setText(category.getName());

            categoryItem.setOnClickListener(view -> onCategoryClickListener.onItemClicked(view, category));

        }

    }

}

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import com.example.blogs.ui.common.OnItemClickListener;

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package com.example.blogs.ui.common;

import android.view.View;

public interface OnItemClickListener<T> {

    void onItemClicked(View view, T data);

}

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package com.example.blogs.ui.categories;

import android.content.Intent;

import android.os.Bundle;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import androidx.annotation.NonNull;

import androidx.core.widget.ContentLoadingProgressBar;

import androidx.fragment.app.Fragment;

import androidx.lifecycle.ViewModelProvider;

import androidx.recyclerview.widget.GridLayoutManager;

import androidx.recyclerview.widget.RecyclerView;

import com.example.blogs.R;

import com.example.blogs.data.model.Category;

import com.example.blogs.ui.blogs.BlogsActivity;

import com.example.blogs.ui.common.OnItemClickListener;

import com.google.gson.Gson;

public class CategoriesFragment extends Fragment {

    private CategoriesAdapter categoryAdapter;

    public View onCreateView(@NonNull LayoutInflater inflater,

                             ViewGroup container, Bundle savedInstanceState) {

        CategoriesViewModel homeViewModel = new ViewModelProvider(this, new CategoriesViewModelFactory()).get(CategoriesViewModel.class);

        View root = inflater.inflate(R.layout.fragment_categories, container, false);

        ContentLoadingProgressBar progress = root.findViewById(R.id.progress);

        RecyclerView categoriesRecyclerView = root.findViewById(R.id.categories_recycler_view);

        OnItemClickListener<Category> onCategoryClickListener = (view, category) -> {

            Intent intent = new Intent(getActivity(), BlogsActivity.class);

            String categoryJson = new Gson().toJson(category);

            intent.putExtra("Category", categoryJson);

            intent.putExtra("CallerActivity", getActivity().getClass().getSimpleName());

            startActivity(intent);

        };

        categoryAdapter = new CategoriesAdapter(root.getContext(), onCategoryClickListener);

        categoriesRecyclerView.setAdapter(categoryAdapter);

        categoriesRecyclerView.setLayoutManager(new GridLayoutManager(root.getContext(), 2));

        progress.show();

        homeViewModel.getCategories().observe(getViewLifecycleOwner(), categories -> {

            categoryAdapter.setCategories(categories);

            progress.hide();

        });

        return root;

    }

}

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<?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=".ui.categories.CategoriesFragment">

    <androidx.core.widget.ContentLoadingProgressBar

        android:id="@+id/progress"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        style="?android:attr/progressBarStyleLarge"

        android:visibility="visible"

        android:indeterminateTint="@color/purple_700"

        app:layout_constraintBottom_toBottomOf="parent"

        app:layout_constraintEnd_toEndOf="parent"

        app:layout_constraintStart_toStartOf="parent" />

    <androidx.recyclerview.widget.RecyclerView

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:id="@+id/categories_recycler_view"

        app:layout_constraintBottom_toBottomOf="parent"

        app:layout_constraintEnd_toEndOf="parent"

        app:layout_constraintStart_toStartOf="parent"

        app:layout_constraintTop_toTopOf="parent"

        />

</androidx.constraintlayout.widget.ConstraintLayout>

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package com.example.blogs.ui.blogs;

import android.content.Intent;

import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;

import androidx.appcompat.widget.Toolbar;

import androidx.fragment.app.FragmentTransaction;

import com.example.blogs.R;

import com.example.blogs.data.model.Category;

import com.google.gson.Gson;

public class BlogsActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_blogs);

        Toolbar toolbar = findViewById(R.id.toolbar);

        setSupportActionBar(toolbar);

        Intent intent = getIntent();

        String categoryJson = intent.getStringExtra("Category");

        Category category = new Gson().fromJson(categoryJson, Category.class);

        setTitle(category.getName());

        String callerActivity = intent.getStringExtra("CallerActivity");

        BlogsFragment fragment = new BlogsFragment();

        Bundle args = new Bundle();

        args.putInt("CategoryId", category.getId());

        args.putString("CallerActivity", callerActivity);

        if (savedInstanceState == null){

            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();

            fragment.setArguments(args);

            ft.replace(R.id.blogs_fragment_container, fragment);

            ft.commit();

        }

    }

}

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<?xml version="1.0" encoding="utf-8"?>

<androidx.coordinatorlayout.widget.CoordinatorLayout 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=".ui.blogs.BlogsActivity">

    <com.google.android.material.appbar.AppBarLayout

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:id="@+id/app_bar"

        android:theme="@style/Theme.Blogs.AppBarOverlay">

        <androidx.appcompat.widget.Toolbar

            android:id="@+id/toolbar"

            android:layout_width="match_parent"

            android:layout_height="?attr/actionBarSize"

            android:background="?attr/colorPrimary"

            app:popupTheme="@style/Theme.Blogs.PopupOverlay" />

    </com.google.android.material.appbar.AppBarLayout>

    <androidx.fragment.app.FragmentContainerView

        android:id="@+id/blogs_fragment_container"

        app:layout_behavior="com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior"

        android:name="androidx.navigation.fragment.NavHostFragment"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        app:defaultNavHost="true"

        app:navGraph="@navigation/mobile_navigation" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

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package com.example.blogs.ui.blogs;

import android.content.Intent;

import android.os.Bundle;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.LinearLayout;

import androidx.annotation.NonNull;

import androidx.core.widget.ContentLoadingProgressBar;

import androidx.fragment.app.Fragment;

import androidx.lifecycle.Observer;