Android聯網簡單應用

Question

應用程序可以正常工作（經過api 23測試，也經過kitkat測試），但是沒有任何顯示，應該顯示圖片（下載並顯示）。 由於我沒有收到任何錯誤，所以我迷路了。 我正在從android初學者的書中尋找代碼，他們建議在4.0（icecream）上測試應用程序，但是在該版本的android studio中沒有推薦的構建。 由於Android在最新API中使用HTTP和聯網的方式發生了一些變化，因此無法正常工作嗎？

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");

}
}

這是logcat：

AndroidManifest.xml文件：

<?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類：

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);
}
}

干得好：

<?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

因為您是初學者，所以我建議您學習如何使用框架。如果沒有框架，使用框架會有很多好處，您將需要實現一些復雜的代碼來進行處理，例如緩存，調整大小，避免內存崩潰，幾乎要處理的所有API的處理等等

對於圖像下載，我建議

畢加索 （我建議最多）

滑行

對於普通的Http請求

凌空抽射

您也可以使用Volley下載圖像。 當您開始學習時，很難理解，但是在您真正了解之后，我保證您不會希望使用常規的HTTPURLConnection來處理任何HTTP請求

如果您需要上傳進度，請告訴我，盡管它非常復雜，但我也會提供代碼。

編輯：

到目前為止，我已經測試過您的代碼，它可以很好地工作，我想為您添加它。

主要活動

    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>

最后添加此清單

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

結果

如果確實不起作用，請考慮檢查模擬器或設備網絡連接。