<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:id="@+id/activity_main"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  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="com.itheima74.internetpicturelook.MainActivity">

  <EditText
    android:id="@+id/et_url"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_alignParentTop="true"
    android:hint="請輸入圖片網址"
    android:inputType="textUri"
    android:text="http://b.hiphotos.baidu.com/image/pic/item/d009b3de9c82d15825ffd75c840a19d8bd3e42da.jpg" />

  <Button
    android:id="@+id/bt_look"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/et_url"
    android:text="查看圖片" />

  <ScrollView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/bt_look"
    android:layout_centerHorizontal="true">

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

</RelativeLayout>

package com.itheima74.internetpicturelook;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;

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

public class MainActivity extends AppCompatActivity {

  private EditText et_url;
  private ImageView iv;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    et_url = (EditText) findViewById(R.id.et_url);
    iv = (ImageView) findViewById(R.id.iv);
    findViewById(R.id.bt_look).setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        String path = et_url.getText().toString().trim();
        if (path.isEmpty()) {
          Toast.makeText(MainActivity.this, "請輸入圖片網址", Toast.LENGTH_SHORT).show();
        } else {
          //開啟子線程去網絡下載圖片
          downLoadPicture(path);
        }
      }

      private void downLoadPicture(final String path) {
        // 子線程請求網絡
        new Thread() {
          @Override
          public void run() {
            try {
              URL url = new URL(path);
              HttpURLConnection connection = (HttpURLConnection) url.openConnection();
              connection.setRequestMethod("GET");
              connection.setConnectTimeout(5000);
              int responseCode = connection.getResponseCode();
              if (responseCode == 200) {
                InputStream inputStream = connection.getInputStream();
                final Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                // 主線程更新UI
                runOnUiThread(new Runnable() {
                  @Override
                  public void run() {
                    iv.setImageBitmap(bitmap);
                  }
                });
              }
            } catch (IOException e) {
              e.printStackTrace();
            }
          }
        }.start();
      }
    });
  }

}