按下“提交”按钮后，应用程序关闭，但如果删除了图像加载，则可以使用

Question

我是Android编程的新手。我正在尝试开发一个应用来查看月刊。

我尝试仅加载第一页。但是，当我单击“提交”按钮时，该应用程序将关闭。如果我删除图像加载部分，则该应用程序可以正常运行。

主要活动和显示活动的代码如下：

主要活动代码

package com.example.mariyanaadam;

import android.content.Intent;
import  android.support.v7.app.AppCompatActivity;
import   android.os.Bundle;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;
import android.widget.AdapterView.OnItemSelectedListener;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button=(Button)findViewById(R.id.button);

// Spinner element
        Spinner spinner = (Spinner) findViewById(R.id.spinner);
        Spinner spinner2 = (Spinner) findViewById(R.id.spinner2);

        // Spinner click listener
        //spinner.setOnItemSelectedListener(this);

        // Spinner Drop down elements
        String [] months ={"January","February","March","April", "May","Jue","July","August","September","October","November","December"};
        ArrayAdapter<String>adapter=new ArrayAdapter<String>(this,android.R.layout.simple_spinner_dropdown_item,months);
        spinner.setAdapter(adapter);
        String [] years ={"2019"};
        ArrayAdapter<String>adapter1=new ArrayAdapter<String>(this,android.R.layout.simple_spinner_dropdown_item,years);
        spinner2.setAdapter(adapter1);


    }

    /** When the user click Submint button */
    public void Display_actvity(View v)
    {
        Spinner spinner = (Spinner) findViewById(R.id.spinner);
        int Month = spinner.getSelectedItemPosition() +1;
        String mth = String.valueOf(Month);
        Spinner spinner2 = (Spinner) findViewById(R.id.spinner2);
        int pos = spinner2.getSelectedItemPosition(); // get selected uten oisutuib
        String yr = (String) spinner2.getItemAtPosition(pos); //get intem name athe posiion
        Intent intent = new Intent(getApplicationContext(), DisplayPage.class);
        intent.putExtra("yr", yr);
        intent.putExtra("mth", mth);
        startActivity(intent);


       /* Toast toast = Toast.makeText(getApplicationContext(),mth,Toast.LENGTH_LONG);
        toast.show();*/
    }

}


DISPLAY PAGE ACITIVITY CODE
package com.example.mariyanaadam;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.os.AsyncTask;
import android.widget.ImageView;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.*;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.ViewGroup;
import android.widget.TextView;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;
import android.widget.AdapterView.OnItemSelectedListener;
public class DisplayPage extends AppCompatActivity {
    public static final String URL =   "http://www.geocities.ws/mariyanaatham/2019/may/1.png";
    ImageView imageView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_display_page);
        Intent intent = getIntent();
        String mth = intent.getStringExtra("mth");
        Integer j = Integer.valueOf(mth);
        String yr = intent.getStringExtra("yr");
        String Month ="";
        if((j<5) &&  (Integer.valueOf(yr)==2019))
            {
                Toast toast =  Toast.makeText(getApplicationContext(),"Megazine Not Available",Toast.LENGTH_LONG);
                toast.show();
            }

        switch(j){
            case 1:
                {
                   Month ="jan";
                    break;
                }
            case 2:
            {
                Month ="feb";
                break;
            }
            case 3:
            {
                Month ="mar";
                break;
            }
            case 4:
            {
                Month ="apr";
                break;
            }
            case 5:
            {
                Month ="may";
                break;
            }
            case 6:
            {
                Month ="jun";
                break;
            }
         }
        //Image loading section
        imageView = (ImageView) findViewById(R.id.imageView);

        // Create an object for subclass of AsyncTask
        GetXMLTask task = new GetXMLTask();
        // Execute the task
        task.execute(new String[] { URL });

    }
    private class GetXMLTask extends AsyncTask<String, Void, Bitmap> {
        @Override
        protected Bitmap doInBackground(String... urls) {
            Bitmap map = null;
            for (String url : urls) {
                map = downloadImage(url);
            }
            return map;
        }

        // Sets the Bitmap returned by doInBackground
        @Override
        protected void onPostExecute(Bitmap result) {
            imageView.setImageBitmap(result);
        }

        // Creates Bitmap from InputStream and returns it
        private Bitmap downloadImage(String url) {
            Bitmap bitmap = null;
            InputStream stream = null;
            BitmapFactory.Options bmOptions = new BitmapFactory.Options();
            bmOptions.inSampleSize = 1;

            try {
                stream = getHttpConnection(url);
                bitmap = BitmapFactory.
                        decodeStream(stream, null, bmOptions);
                stream.close();
            } catch (IOException e1) {
                e1.printStackTrace();
            }
            return bitmap;
        }

        // Makes HttpURLConnection and returns InputStream
        private InputStream getHttpConnection(String urlString)
                throws IOException {
            InputStream stream = null;
            URL url = new URL(urlString);
            URLConnection connection = url.openConnection();

            try {
                HttpURLConnection httpConnection = (HttpURLConnection) connection;
                httpConnection.setRequestMethod("GET");
                httpConnection.connect();

                if (httpConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
                    stream = httpConnection.getInputStream();
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }
            return stream;
        }
    }
}

杂志的页面以png文件的形式存储在Web服务器中。当用户选择月份和年份然后单击提交按钮时，页面将以不同的图像视图加载到水平滚动条中。