Android实战简易教程-第七十一枪（异步网络下载网络图片及图片廊制作）

首先来实现异步下载网络图片，布局文件如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/btn_getpic"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="获取数图片" />

    <ImageView
        android:id="@+id/img"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

网络请求类，继承Thread：

package com.test.demo;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.widget.ImageView;

public class LoadThread extends Thread {
	private String url;
	private Handler handler;
	private ImageView imageView;

	public LoadThread(String url, Handler handler, ImageView imageView) {
		this.url = url;
		this.handler = handler;
		this.imageView = imageView;
	}

	@Override
	public void run() {
		try {
			ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
			URL conn = new URL(url);
			HttpURLConnection httpURLConnection = (HttpURLConnection) conn.openConnection();
			InputStream in = httpURLConnection.getInputStream();
			byte data[] = new byte[2 * 1024];
			int len = 0;
			while ((len = in.read(data)) != -1) {
				byteArrayOutputStream.write(data, 0, len);
			}
			final Bitmap bitmap = BitmapFactory.decodeByteArray(byteArrayOutputStream.toByteArray(), 0,
					byteArrayOutputStream.toByteArray().length);
			handler.post(new  Runnable() {
				public void run() {
					imageView.setImageBitmap(bitmap);
				}
			});

		} catch (MalformedURLException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {

		}

	}

}

构造方法需要传入请求的URL地址，ImageView控件和Handler对象，方便将结果返回到UI线程，覆写了run方法，并且在run方法中编写了网络请求的方法，最后调用Handler的post方法，将请求结果反映到UI的ImageView上。对网络请求IO部分不熟悉的同学可以学习一下这部分知识，编写套路都是固定的。

MainActivity.java:

package com.test.demo;

import com.example.testandroid.R;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity {
	private Button btn;
	private ImageView img;
	private String url = "http://pic.yesky.com/uploadImages/2016/065/03/8VG0Q0HU97X3.jpg";
	private Handler handler = new Handler();

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		btn = (Button) findViewById(R.id.btn_getpic);
		btn.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				new LoadThread(url, handler, img).start();
			}
		});
		img = (ImageView) findViewById(R.id.img);
	}
}

注意--此应用需要配置网络权限。配置权限后运行项目如下：

下面可以添加一个向上和向下的按钮，实现图片切换，main.xml代码如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <ImageView
        android:id="@+id/img"
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:layout_alignParentTop="true" />

    <Button
        android:id="@+id/btn_pre"
        android:layout_width="150dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/img"
        android:text="上一张" />

    <Button
        android:id="@+id/btn_next"
        android:layout_width="150dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/img"
        android:layout_alignParentRight="true"
        android:text="下一张" />

</RelativeLayout>

MainActivity.java修改如下：

package com.test.demo;

import com.example.testandroid.R;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity implements OnClickListener {
	private ImageView imageView;
	private Button buttonNext;
	private Button buttonPre;
	private String urls[] = { "http://pic.yesky.com/uploadImages/2016/065/03/8VG0Q0HU97X3.jpg",
			"http://img.sc115.com/hb/yl1/23/88160202491142.jpg",
			"http://pic.yesky.com/uploadImages/2016/065/48/2A05DMJ41LAN.jpg",
			"http://img4q.duitang.com/uploads/item/201408/12/20140812200853_vVnz2.png" };
	private Handler handler = new Handler();
	private int i=0;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		imageView = (ImageView) findViewById(R.id.img);
		buttonNext = (Button) findViewById(R.id.btn_next);
		buttonPre = (Button) findViewById(R.id.btn_pre);
		buttonNext.setOnClickListener(this);
		buttonPre.setOnClickListener(this);
		new LoadThread(urls[0], handler, imageView).start();

	}

	@Override
	public void onClick(View v) {

		switch (v.getId()) {
		case R.id.btn_next:
			i++;
			new LoadThread(urls[i%4], handler, imageView).start();
			Toast.makeText(MainActivity.this, i%4+"", Toast.LENGTH_SHORT).show();

			break;

		case R.id.btn_pre:
			if(i>0){
				i--;}
				else{
					i=3;
				}
			new LoadThread(urls[i%4], handler, imageView).start();
			Toast.makeText(MainActivity.this, i%4+"", Toast.LENGTH_SHORT).show();

			break;
		}

	}

}

其中注意图片下标的逻辑处理！

运行实例如下：

源码下载

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