在 Android 上下载 imageview 的图像

Question

我看过这个问题：android how to download an 1mb image file and set to ImageView
它不能解决我的问题，因为它只显示了如何在 您已经拥有位图之后显示它。

我正在尝试从 URL 下载图像，以便在 Android 设备上与 ImageView 一起显示。我不知道该怎么做。

我在互联网上看了一些，这是我到目前为止的代码：

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    //Set local image
    ImageView image = (ImageView) findViewById(R.id.test_image);
    image.setImageResource(R.drawable.test2);

    //Prepare to download image
    URL url;        
    InputStream in;

    //BufferedInputStream buf;
    try {
        url = new URL("http://i.imgur.com/CQzlM.jpg");
        in = url.openStream();

        out = new BufferedOutputStream(new FileOutputStream("testImage.jpg"));
        int i;

         while ((i = in.read()) != -1) {
             out.write(i);
         }
         out.close();
         in.close();

        buf = new BufferedInputStream(in);
        Bitmap bMap = BitmapFactory.decodeStream(buf);
        image.setImageBitmap(bMap);
        if (in != null) {
        in.close();
        }
        if (buf != null) {
        buf.close();
        }
    } catch (Exception e) {
        Log.e("Error reading file", e.toString());
    }
}

Answer 1

代码可能会起作用，尽管您正在主线程上下载图像。这意味着当下载时间超过 5 秒时，您将看到著名的 ANR 对话框，并且您的应用程序将崩溃...

您应该在后台线程中下载您的图像，并将结果发布回您的主线程。回到主线程，您可以使用下载的图像更新您的 imageview。

这是一个例子：

package nl.entreco.stackoverflow;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.URL;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;

public class StackOverflowActivity extends Activity {

//  
private ImageView mImageView;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    //Find the reference to the ImageView
    mImageView = (ImageView) findViewById(R.id.test_image);

    // You can set a temporary background here
    //image.setImageResource(null);

    // Start the DownloadImage task with the given url
    new DownloadImage().execute("http://i.imgur.com/CQzlM.jpg");
}


/**
 * Simple functin to set a Drawable to the image View
 * @param drawable
 */
private void setImage(Drawable drawable)
{
    mImageView.setBackgroundDrawable(drawable);
}

public class DownloadImage extends AsyncTask<String, Integer, Drawable> {

    @Override
    protected Drawable doInBackground(String... arg0) {
        // This is done in a background thread
        return downloadImage(arg0[0]);
    }

    /**
     * Called after the image has been downloaded
     * -> this calls a function on the main thread again
     */
    protected void onPostExecute(Drawable image)
    {
        setImage(image);
    }


    /**
     * Actually download the Image from the _url
     * @param _url
     * @return
     */
    private Drawable downloadImage(String _url)
    {
        //Prepare to download image
        URL url;        
        BufferedOutputStream out;
        InputStream in;
        BufferedInputStream buf;

        //BufferedInputStream buf;
        try {
            url = new URL(_url);
            in = url.openStream();

            /*
             * THIS IS NOT NEEDED
             * 
             * YOU TRY TO CREATE AN ACTUAL IMAGE HERE, BY WRITING
             * TO A NEW FILE
             * YOU ONLY NEED TO READ THE INPUTSTREAM 
             * AND CONVERT THAT TO A BITMAP
            out = new BufferedOutputStream(new FileOutputStream("testImage.jpg"));
            int i;

             while ((i = in.read()) != -1) {
                 out.write(i);
             }
             out.close();
             in.close();
             */

            // Read the inputstream 
            buf = new BufferedInputStream(in);

            // Convert the BufferedInputStream to a Bitmap
            Bitmap bMap = BitmapFactory.decodeStream(buf);
            if (in != null) {
                in.close();
            }
            if (buf != null) {
                buf.close();
            }

            return new BitmapDrawable(bMap);

        } catch (Exception e) {
            Log.e("Error reading file", e.toString());
        }

        return null;
    }

}

}

不要忘记将permission.INTERNET添加到你的manifest中，如果没有，你会得到一个错误...