在Android上下载imageview的图片 [英] Download image for imageview on Android

问题描述

我看过这个问题： android如何下载1mb图像文件并设置为ImageView

它不能解决我的问题，因为它只显示如何在之后显示您已经拥有的位图。

I have seen this question: android how to download an 1mb image file and set to ImageView
It does not solve my problem as it only shows how to display the bitmap after you already have it.

我正在尝试下载来自网址的图片，以便在Android设备上使用ImageView进行显示。我不知道该怎么做。

I am trying to download an image from a URL to have it be displayed with an ImageView on an Android device. I am not sure how to do this.

我已经在网路上看了一下，这是迄今为止的代码：

I've looked around a bit on the internet, this is the code I have so far:

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());
    }
}

推荐答案

代码可能会起作用，所有这些都是在主线程上下载您的图像。这意味着下载需要5秒钟以上时，您将看到着名的ANR对话框，您的应用程序将崩溃...

The code would probably work, alltough you are downloading your image on your main thread. This means that when it takes more than 5 seconds to download, you will be presented with the famous ANR dialog, and your app will crash...

您应该下载在后台线程中的图像，并将结果发回主线程。回到主线程，您可以使用下载的图像更新您的图像视图。

You should download your image in a background thread, and post the result back to your main thread. Back in the main thread, you can update your imageview with the downloaded image.

以下是一个示例：

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添加到您的清单，否则，您将收到错误...

Don't forget to add the permission.INTERNET to your manifest, if not, you will get an error...

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