AsyncTask再度学习

最后更新于:2022-04-01 14:43:10

上篇文章写到了简单的文件下载的功能,这里再简单的添加一个功能(显示下载进度)。代码方面改变不大,只是运用了AsyncTask的onProgressUpdate函数,不过下载图片的代码得要用另外一种方式写了。
package com.example.myasynctask;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.http.HttpEntity;
import org.apache.http.HttpRequest;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity {
    private Button button;
    private ImageView iv;
    private String path = "http://cdn.duitang.com/uploads/item/201310/17/20131017194234_eZfFU.thumb.600_0.png";
    private ProgressDialog dia;

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

        dia = new ProgressDialog(this);
        dia.setTitle("提示信息");
        dia.setMessage("正在下载...");
        dia.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);

        button.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                new myTask().execute(path);
            }
        });
    }

    private class myTask extends AsyncTask<String, Integer, Bitmap> {
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            dia.show();
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            // TODO Auto-generated method stub
            super.onProgressUpdate(values);
            dia.setProgress(values[0]);
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            // TODO Auto-generated method stub
            Bitmap bitmap = null;

            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
            InputStream inputStream = null;

            HttpClient httpClient = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet(params[0]);
            try {
                HttpResponse httpResponse = httpClient.execute(httpGet);
                if (httpResponse.getStatusLine().getStatusCode() == 200) {
                    long total_length = httpResponse.getEntity()
                            .getContentLength();
                    int has_read = 0;
                    int total_read = 0;
                    byte[] data = new byte[1024];
                    inputStream = httpResponse.getEntity().getContent();
                    while ((has_read = inputStream.read(data)) != -1) {
                        total_read += has_read;
                        outputStream.write(data, 0, has_read);
                        int value = (int) (total_read / (float) total_length * 100);
                        publishProgress(value);
                    }

                    byte[] result = outputStream.toByteArray();
                    bitmap = BitmapFactory.decodeByteArray(result, 0,
                            result.length);

                }
            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return bitmap;
        }

        @Override
        protected void onPostExecute(Bitmap result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            iv.setImageBitmap(result);
            dia.dismiss();
        }

    }
}
                </div>
    
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