AsyncTask<String, Integer, Bitmap>异步加载

最新推荐文章于 2021-03-20 14:36:48 发布

原创最新推荐文章于 2021-03-20 14:36:48 发布 · 1.3k 阅读

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#android #异步加载

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本文介绍了一个使用Android中的AsyncTask从网络加载图片到ImageView的示例应用。该应用包含一个按钮，点击后会显示进度对话框并开始下载图片。下载过程中更新进度条，并在完成后将图片显示在界面上。

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package com.example.android_asynctask;

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

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 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.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity {
	//http://c.hiphotos.baidu.com/image/w%3D2048/sign=eb9ed52bb11bb0518f24b4280242dbb4/f603918fa0ec08fa13d4caae5bee3d6d54fbdae7.jpg
	private String url="http://c.hiphotos.baidu.com/image/w%3D2048/sign=eb9ed52bb11bb0518f24b4280242dbb4/f603918fa0ec08fa13d4caae5bee3d6d54fbdae7.jpg";
	private ImageView imageView;
	private Button button;
	private ProgressDialog progressDialog;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		imageView=(ImageView) findViewById(R.id.imageView1); 
		button=(Button) findViewById(R.id.button1);
		progressDialog=new ProgressDialog(this);
		progressDialog.setTitle("提示");
		progressDialog.setMessage("正在下载，请稍后。。。。");
		progressDialog.setCancelable(false);
		progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
		button.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				new MyTask().execute(url);
			}
		});
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}
	public class MyTask extends AsyncTask<String, Integer, Bitmap>{
		
		@Override
		protected void onPreExecute() {
			// TODO Auto-generated method stub
			super.onPreExecute();
			progressDialog.show();
		}
		@Override
		protected void onProgressUpdate(Integer... values) {
			// TODO Auto-generated method stub
			super.onProgressUpdate(values);
			progressDialog.setProgress(values[0]);
		}
		@Override
		protected Bitmap doInBackground(String... params) 
		{
			// TODO Auto-generated method stub
			Bitmap bitmap=null;
			ByteArrayOutputStream byteArrayOutputStream=new ByteArrayOutputStream();
			InputStream inputStream=null;
			try {
				HttpClient httpClient=new DefaultHttpClient();
				HttpGet httpGet=new HttpGet(params[0]);
				HttpResponse httpResponse=httpClient.execute(httpGet);Log.i("Main", "标记2");
				int responseCode=httpResponse.getStatusLine().getStatusCode();
				if(responseCode==200){
					inputStream=httpResponse.getEntity().getContent();
					long file_length=httpResponse.getEntity().getContentLength();
					byte[] data=new byte[1024];
					int len=0;
					int total_length=0;
					int values=0;
					
					while((len=inputStream.read(data))!=-1){
						total_length+=len;
						values=(int) ((total_length/(float)file_length)*100);	
						publishProgress(values);
						byteArrayOutputStream.write(data, 0, len);
					}
					byte[] result=byteArrayOutputStream.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();
			}finally{
				if(inputStream!=null){
					try {
						inputStream.close();
					} catch (IOException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
				}
				if(byteArrayOutputStream!=null){
					try {
						byteArrayOutputStream.close();
					} 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);
			progressDialog.dismiss();
			imageView.setImageBitmap(result);
		}
	}
}