Android 显示网络图片

本文内容

• 环境
• 演示显示网络图片

本文演示 Android 如何显示网络图片。学习一门新的语言，最好办法就先了解该语言的语法和库，以及设计思想，再着手现实一些常用功能，毕竟以后用该语言是要写程序的，而程序说白了，就是一个个功能点。

环境

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• Windows 2008 R2 64 位
• Eclipse ADT V22.6.2，Android 4.4.3
• 三星 SM-G3508，Android OS 4.1

演示显示网络图片

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利用一个新线程加载并显示网络图片，并使用 handler 传递消息，若无异常，则用 Toast 现实“加载图片….”，否则，若网络图片不存在，显示“图片不存在”。同时，自定义一个类 HttpUtils，负责用 HTTP 访问网络。Android 程序如下图所示。

图 1

XML 页面文件略，只是添加 ImageView 和 Button 控件，核心代码如下：

自定义 HttpUtils 类

使用 HTTP 协议访问网络图片。

package com.example.viewwebimagedemo.utils;

import java.io.IOException;

import java.io.InputStream;

import java.net.HttpURLConnection;

import java.net.URL;

public class HttpUtils {

    private final static String URL_PATH = "http://images.cnblogs.com/cnblogs_com/liuning8023/588559/o_Android.jpg";

    public HttpUtils() {

        // TODO Auto-generated constructor stub

    }

    public static InputStream getImageViewInputStream() throws IOException {

        InputStream inputStream = null;

        URL url = new URL(URL_PATH);

        if (url != null) {

            HttpURLConnection httpURLConnection = (HttpURLConnection) url

                    .openConnection();

            httpURLConnection.setConnectTimeout(3000);

            httpURLConnection.setRequestMethod("GET");

            httpURLConnection.setDoInput(true);

            int response_code = httpURLConnection.getResponseCode();

            if (response_code == 200) {

                inputStream = httpURLConnection.getInputStream();

            }

        }

        return inputStream;

    }

}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

MainActivity 类

负责加载并显示网络图片。

package com.example.viewwebimagedemo;

import java.io.InputStream;

import com.example.viewwebimagedemo.R;

import com.example.viewwebimagedemo.utils.HttpUtils;

import android.app.Activity;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.os.Bundle;

import android.os.Handler;

import android.os.Looper;

import android.os.Message;

import android.view.View;

import android.widget.Button;

import android.widget.ImageView;

import android.widget.Toast;

public class MainActivity extends Activity {

    private Button button;

    private ImageView imageView;

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        button = (Button) this.findViewById(R.id.btn);

        imageView = (ImageView) this.findViewById(R.id.imageView);

        button.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                new Thread(access).start();

            }

        });

    }

    // 获得图片

    public void getImg() {

        try {

            InputStream inputStream = HttpUtils.getImageViewInputStream();

            Bitmap bitmap = BitmapFactory.decodeStream(inputStream);

            Looper.prepare();// 必须调用此方法，要不然会报错

            Message msg = new Message();

            msg.what = 0;

            msg.obj = bitmap;

            handler.sendMessage(msg);

        } catch (Exception e) {

            Toast.makeText(getApplicationContext(), "获取图片错误", 1).show();

        }

    }

    // 加载图片

    private void setImg(Bitmap bm) {

        imageView.setImageBitmap(bm);

    }

    // 另一个线程从网络获得图片

    private Runnable access = new Runnable() {

        @Override

        public void run() {

            getImg();

        }

    };

    // 更新UI信息

    private Handler handler = new Handler() {

        @Override

        public void handleMessage(Message msg) {

            if (msg.what == 0) {

                if (msg.obj == null) {

                    Toast.makeText(getApplicationContext(), "图片不存在", 1).show();

                } else {

                    Toast.makeText(getApplicationContext(), "加载图片...", 1)

                            .show();

                    setImg((Bitmap) msg.obj);

                }

            }

        }

    };

}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

授权 Android 访问网络权限

修改 AndroidManifest.xml 文件，添加授权 Android 访问网络的权限。

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

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

若直接在 Activity 的 onCreate 事件里加载并显示图片，如下所示：

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        // 假设已经从网络获得 bitmap

        imageView = (ImageView) this.findViewById(R.id.imageView);

        imageView.setImageBitmap(bitmap);

    }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

会报 android.os.NetworkOnMainThreadException 异常。因为，Android 4.x 之后，不允许在主线程进行网络访问。

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