java - 我如何使用 AsyncTask 下载和阅读“PDF 文件”

Question

我正在为学生创建一个应用程序，这样他们就不会错过他们的大量书籍。在这个项目中，学生点击“RecylerView”，立即下载“Pdf”书并保存到外部存储。没有数据库的“喜欢whatsapp”

目前，我有一个问题，它只看到文件，但不保存！

我正在使用底部的AsyscTask “我的 PDF 查看器”活动

请帮忙！！！

我的主要活动

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.RelativeLayout;

import java.util.ArrayList;
import java.util.List;

> public class MainActivity extends AppCompatActivity {
    List<Product> productList;

    //the recyclerview
    RecyclerView recyclerView;

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



        Animation animation = AnimationUtils.loadAnimation(this, R.anim.anim_about_card_show);
        RelativeLayout relativeLayout = findViewById(R.id.rl);
        relativeLayout.startAnimation(animation);
        //getting the recyclerview from xml
        recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));


        //initializing the productlist
        productList = new ArrayList<>();


        //adding some items to our list
        productList.add(
                new Product(
                        1,
                        "TEst 11111 \n",
                        60000,
                        R.drawable.android,
                        "link1"

                ));

        productList.add(
                new Product(
                        1,
                        " More types, Methods, Conditionals \n",

                        60000,
                        R.drawable.android,
                        "link2"
                                            ));

        productList.add(
                new Product(
                        1,
                        "Loops, Arrays ",


                        60000,
                        R.drawable.android,
                        "lin3"
                ));
        productList.add(
                new Product(
                        1,
                        "Strings",
                        60000,
                        R.drawable.android,
                        "https://firebasestorage.googleapis.com/v0/b/firepdf-4c1d6.appspot.com/o/2.intro.pdf?alt=media&token=75731b04-c1e7-42c4-b988-e50a8f7e5f6b    "
                ));


        //creating recyclerview adapter
        ProductAdapter adapter = new ProductAdapter(this, productList);

        //setting adapter to recyclerview
        recyclerView.setAdapter(adapter);
    }

}

适配器

import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.support.v7.widget.CardView;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.List;


> public class ProductAdapter extends RecyclerView.Adapter<ProductAdapter.ProductViewHolder> {

    //this context we will use to inflate the layout
    private Context mCtx;

    //we are storing all the products in a list
    private List<Product> productList;

    //getting the context and product list with constructor
    public ProductAdapter(Context mCtx, List<Product> productList) {
        this.mCtx = mCtx;
        this.productList = productList;
    }

    @Override
    public ProductViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        //inflating and returning our view holder
        LayoutInflater inflater = LayoutInflater.from(mCtx);
        View view = inflater.inflate(R.layout.layout_products, null);
        return new ProductViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ProductViewHolder holder, final int position) {
        //getting the product of the specified position
        final Product product = productList.get(position);

        //binding the data with the viewholder views

        holder.textViewTitle.setText(product.getTitle());


        holder.imageView.setImageDrawable(mCtx.getResources().getDrawable(product.getImage()));

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

                Intent i = new Intent(v.getContext(), pdf.class);
                i.putExtra("title",productList.get(position).getTitle());
                i.putExtra("product",productList.get(position).getTitle());
                i.putExtra("link",productList.get(position).getLink());
                mCtx.startActivity(i);

            }
        });
    }


    @Override
    public int getItemCount() {
        return productList.size();
    }


    class ProductViewHolder extends RecyclerView.ViewHolder {

        TextView textViewTitle;
        ImageView imageView;
        CardView cardView;

        public ProductViewHolder(View itemView) {
            super(itemView);
            cardView = itemView.findViewById(R.id.cardview);// card intial
            textViewTitle = itemView.findViewById(R.id.textViewTitle);
            imageView = itemView.findViewById(R.id.imageView);
        }
    }
}

我的 PDF 查看器

import android.app.ProgressDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.MenuItem;
import android.widget.Toast;

import com.github.barteksc.pdfviewer.PDFView;


import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;


public class pdf extends AppCompatActivity {
    String link="",productList="",product="";
    PDFView pdfView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_pdf);
        product =getIntent().getStringExtra("title");
        productList=getIntent().getStringExtra("productList");
        link=getIntent().getStringExtra("link");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        getSupportActionBar().setTitle(productList);
        pdfView=findViewById(R.id.pdfv);
        //pdfView.fromAsset(link).load();



        if (isConnected()) {
            Toast.makeText(getApplicationContext(), "Internet Connected", Toast.LENGTH_SHORT).show();


        } else {
            Toast.makeText(getApplicationContext(), "No Internet Connection", Toast.LENGTH_SHORT).show();

            AlertDialog.Builder builder = new AlertDialog.Builder(pdf.this);
            builder.setTitle("NoInternet Connection Alert")
                    .setMessage("GO to Setting ?")
                    .setCancelable(false)
                    .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            startActivity(new Intent(android.provider.Settings.ACTION_WIRELESS_SETTINGS));
                        }
                    })
                    .setNegativeButton("No", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            Toast.makeText(pdf.this,"Go Back TO HomePage!",Toast.LENGTH_SHORT).show();
                        }
                    });
            //Creating dialog box
            AlertDialog dialog  = builder.create();
            dialog.show();
        }




        Bundle bundle = getIntent().getExtras();
        if (bundle != null) {
            link = getIntent().getStringExtra("link");
        }
        new pdf.RetrievePDFStream().execute(link);
    }


    public boolean isConnected() {
        boolean connected = false;
        try {
            ConnectivityManager cm = (ConnectivityManager)getApplicationContext().getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo nInfo = cm.getActiveNetworkInfo();
            connected = nInfo != null && nInfo.isAvailable() && nInfo.isConnected();
            return connected;
        } catch (Exception e) {
            Log.e("Connectivity Exception", e.getMessage());
        }
        return connected;
    }


    class RetrievePDFStream extends AsyncTask<String, Void, InputStream> {

        ProgressDialog progressDialog;
        protected void onPreExecute()
        {
            progressDialog = new ProgressDialog(pdf.this);
            progressDialog.setTitle("getting the book content...");
            progressDialog.setMessage("Please wait...");
            progressDialog.setCanceledOnTouchOutside(false);
            progressDialog.show();



        }
        @Override
        protected InputStream doInBackground(String... strings) {
            InputStream inputStream = null;

            try {

                URL urlx = new URL(strings[0]);
                HttpURLConnection urlConnection = (HttpURLConnection) urlx.openConnection();
                if (urlConnection.getResponseCode() == 200) {
                    inputStream = new BufferedInputStream(urlConnection.getInputStream());

                }
            } catch (IOException e) {
                return null;
            }
            return inputStream;

        }

        @Override
        protected void onPostExecute(InputStream inputStream) {
            pdfView.fromStream(inputStream).load();
            progressDialog.dismiss();
        }
    }
    @Override public boolean onOptionsItemSelected(MenuItem item)
    {
        if (item.getItemId() == android.R.id.home)//means home default hai kya yesok
        {
            onBackPressed();
            return true;
        }
        return false;
    }
}

标签： javaandroidpdfandroid-recyclerviewandroid-asynctask