练习：从网络中获取图片以及多线程的使用

1..0结果：

从输入框（editortext）输入网页图片地址，点击按钮（Button），将图片拉取到（imageView）中显示

1.1结果图：



2.0分析：

在高版本的android中为了用户体验，联网功能必须实现在子线程，原因在于主线程是UI线程，频繁在UI线程执行长时间的联网操作会导致UI卡顿。当子线程需要更新UI时应该采用handler来处理。

3.0代码：

mainActivity：

package com.example.see_pic;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URL;
import java.net.URLConnection;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.text.TextUtils;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {
	private EditText edt_view;
	private ImageView img_view;
	public static final int SHOW_IMAGE = 1;
	private Handler handler = new Handler() {
		public void handleMessage(Message msg) {
			switch (msg.what) {
			case SHOW_IMAGE:
				Bitmap bitmap = (Bitmap) msg.obj;
				img_view.setImageBitmap(bitmap);
				break;
			default:
				break;
			}

		};
	};

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		getview();// 获取控件
	}

	public void showImage(View view) {
		final String path = edt_view.getText().toString();
		if (TextUtils.isEmpty(path)) {
			Toast.makeText(MainActivity.this, "图片路径不能为空", Toast.LENGTH_LONG)
					.show();
		} else {
			new Thread() {// 匿名内部类
				public void run() {

					try {
						URL url = new URL(path);
						HttpURLConnection httpURLConnection = (HttpURLConnection) url
								.openConnection();// 打开链接
						httpURLConnection.setRequestMethod("GET");
						httpURLConnection.setConnectTimeout(5000);// 超时时间
						int responsecode = httpURLConnection.getResponseCode();// 获取响应码
						if (responsecode == 200) {
							InputStream is = httpURLConnection.getInputStream();
							Bitmap bitmap = BitmapFactory.decodeStream(is);
							Message msg = new Message();//要处理的 是图片(Message)
							msg.what = SHOW_IMAGE;//调用上面的handlerMessage
							msg.obj = bitmap;// 将位图bitmap放入msg
							handler.sendMessage(msg);//把消息传给主线程
						} else {
							Toast.makeText(MainActivity.this, "加载图片超时或失败",
									Toast.LENGTH_LONG).show();
						}
					} catch (MalformedURLException e) {
						e.printStackTrace();
					} catch (IOException e) {
						e.printStackTrace();
					}
				};

			}.start();
		}
	}

	/*
	 * 获取控件方法
	 */
	private void getview() {
		img_view = (ImageView) findViewById(R.id.img_view);
		edt_view = (EditText) findViewById(R.id.edt_view);
	}

	@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;
	}

}

Activity_Main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <ImageView
        android:id="@+id/img_view"
        android:layout_width="278dp"
        android:layout_height="279dp"
        android:src="@drawable/ic_launcher" />

    <EditText
        android:id="@+id/edt_view"
        android:layout_width="262dp"
        android:layout_height="58dp"
        android:ems="10"
        android:text="http://v1.qzone.cc/skin/201408/06/19/46/53e215a4ca0c5991.jpg!600x600.jpg" />

    <Button
        android:id="@+id/btn_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:onClick="showImage"
        android:text="浏览" />

</LinearLayout>

AndroidManifest.xml中添加联网权限：

<uses-permission android:name="android.permission.INTERNET"/>

4.0相关下载

http://download.csdn.net/detail/yyd_diablo/8833127