Android联网简单应用

Question

App works(api 23 tested also kitkat tested), but nothing shows, it should show picture(download it and put it in view). Since I am not getting any error, I am lost. I am looking from android beginner book for code, and they suggest apps to be tested on 4.0(icecream) but there is no recommended build in android studio for that version. Is it not working because of some change in how android works with HTTP and networking in latest APIs?

public class NetworkingActivity extends Activity {

ImageView img;

private InputStream OpenHttpConnection(String urlString)
        throws IOException
{
    InputStream in = null;
    int response = -1;

    URL url = new URL(urlString);
    URLConnection conn = url.openConnection();

    if (!(conn instanceof HttpURLConnection))
        throw new IOException("Not an HTTP connection");
    try{
        HttpURLConnection httpConn = (HttpURLConnection) conn;
        httpConn.setAllowUserInteraction(false);
        httpConn.setInstanceFollowRedirects(true);
        httpConn.setRequestMethod("GET");
        httpConn.connect();
        response = httpConn.getResponseCode();
        if (response == HttpURLConnection.HTTP_OK) {
            in = httpConn.getInputStream();
        }
    }
    catch (Exception ex)
    {
        Log.d("Networking", ex.getLocalizedMessage());
        throw new IOException("Error connecting");
    }
    return in;
}

private Bitmap DownloadImage(String URL)
{
    Bitmap bitmap = null;
    InputStream in = null;
    try {
        in = OpenHttpConnection(URL);
        bitmap = BitmapFactory.decodeStream(in);
        in.close();
    } catch (IOException e1) {
        Log.d("NetworkingActivity", e1.getLocalizedMessage());
    }
    return bitmap;
}

private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
    protected Bitmap doInBackground(String... urls) {
        return DownloadImage(urls[0]);
    }

    protected void onPostExecute(Bitmap result) {
        ImageView img = (ImageView) findViewById(R.id.img);
        img.setImageBitmap(result);
    }
}

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    new DownloadImageTask().execute("http://www.mayoff.com/5-01cablecarDCP01934.jpg");

}
}

Here is logcat:

AndroidManifest.xml file:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="metropolitan.com.desetopredavanjeprotokoli10">

<uses-permission android:name="android.permission.INTERNET"/>

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

MainActivity class:

package metropolitan.com.desetopredavanjeprotokoli10;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

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

Here you go:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout    xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Smor"
    android:layout_gravity="center"/>

<ImageView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/img"
    android:layout_gravity="center"/>
</RelativeLayout>

Answer 1

Since you are beginer I suggest your learn how to use framework There a lot of benefit using framework if not you will need to implement some complex code for handling such as caching,resizing,avoiding memory crash,handling for almost all API which you are facing etc.

For image download i suggest

Picasso (which i suggest most)

Glide

For normal Http request

Volley

You can us Volley to download image as well. When you start learning it is kind a hard to understand but after u really get understading I promise you will not wan to use regular HTTPURLConnection to handle any HTTP Request

If you need upload with progress please let me know I will give add the code as well although it is much complicated.

Edited:

So far I have been test out your code it work perfectly fine.I would like to add it for you.

MainActivity

    ImageView img;

    private InputStream OpenHttpConnection(String urlString)
            throws IOException
    {
        InputStream in = null;
        int response = -1;

        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();

        if (!(conn instanceof HttpURLConnection))
            throw new IOException("Not an HTTP connection");
        try{
            HttpURLConnection httpConn = (HttpURLConnection) conn;
            httpConn.setAllowUserInteraction(false);
            httpConn.setInstanceFollowRedirects(true);
            httpConn.setRequestMethod("GET");
            httpConn.connect();
            response = httpConn.getResponseCode();
            if (response == HttpURLConnection.HTTP_OK) {
                in = httpConn.getInputStream();
                Log.d("asd","OK");
            }else{
                Log.d("asd","error");
            }
        }
        catch (Exception ex)
        {
            Log.d("Networking", ex.getLocalizedMessage());
            throw new IOException("Error connecting");
        }
        return in;
    }

    private Bitmap DownloadImage(String URL)
    {
        Bitmap bitmap = null;
        InputStream in = null;
        try {
            in = OpenHttpConnection(URL);
            Log.d("in", String.valueOf(in));
            bitmap = BitmapFactory.decodeStream(in);
            in.close();
        } catch (IOException e1) {
            Log.d("NetworkingActivity", e1.getLocalizedMessage());
        }
        return bitmap;
    }

    private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {

        protected Bitmap doInBackground(String... urls) {
            Log.d("aSD","ASD");
            return DownloadImage(urls[0]);
        }

        protected void onPostExecute(Bitmap result) {
            ImageView img = (ImageView) findViewById(R.id.img);
            img.setImageBitmap(result);
        }
    }

    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        new DownloadImageTask().execute("http://www.mayoff.com/5-01cablecarDCP01934.jpg");

    }

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.myapplication.MainActivity">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/img"/>
</RelativeLayout>

Last add this to manifest

    <uses-permission android:name="android.permission.INTERNET"/>

Result

If it really not working consider check your emulator or device network connection.