两种方式实现网络图片查看器

分别采用两种方法实现网络图片查看器。
效果如图所示。

微信截图_20171121124018.png

• 01 在子线程里面执行耗时操作，在主线程更新UI

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    private Button button;
    private ImageView imageView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button)findViewById(R.id.bt_view);
        imageView = (ImageView)findViewById(R.id.image_view);
        button.setOnClickListener(this);

    }

    //UI只能在主线程更新，利用Handler来将更新UI的操作从子线程切换到主线程上，即将获取的图片显示在屏幕上
    Handler handler = new Handler(){
        public void handleMessage(Message msg){
            Bitmap bitmap = (Bitmap)msg.obj;
            if(bitmap == null){
                Toast.makeText(MainActivity.this,"获取失败...",Toast.LENGTH_SHORT).show();
            }else{

                imageView.setImageBitmap(bitmap);
            }
        }
    };

    //button点击监听，创建一个子线程处理连接网络获取图片的耗时操作
    public void onClick(View v){
        final String path = "http://192.168.107.2:8080/pro2.png";
        new Thread(new Runnable() {
            @Override
            public void run() {
                //获取Bitmap类型的图片信息
                Bitmap bitmap = getImage(path);
                Message msg = new Message();
                //向Handler传递图片信息
                msg.obj = bitmap;
                handler.sendMessage(msg);
            }
        }).start();
    }
    //获取图片数据
    public Bitmap getImage(String path){
        try {
            //2.获取URL对象
            URL url = new URL(path);
            //3.获取连接对象
            final HttpURLConnection conn = (HttpURLConnection)url.openConnection();
            //4.初始化
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(5000);
            conn.connect();
            //如果conn.getResponseCode()==200，则表示连接成功
            if(conn.getResponseCode() == 200){
                //获取图片数据流
                InputStream is = conn.getInputStream();
                //BitmapFactory加工成Bitmap格式
                Bitmap bitmap = BitmapFactory.decodeStream(is);
                return bitmap;
            }
        } catch (Exception e) {
            e.printStackTrace();

        }
        return null;
    }
}

• 02 使用异步机制AsyncTask

public class MainActivity extends AppCompatActivity{

    private Button button;
    private ImageView imageView;
    private GetNetPic getPic;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button)findViewById(R.id.bt_view);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String path = "http://192.168.107.2:8080/pro2.png";
                getPic = new GetNetPic();
                //这里是调用execute()方法，触发异步任务的执行
                getPic.execute(path);
            }
        });
        imageView = (ImageView)findViewById(R.id.image_view);
    }

    class GetNetPic extends AsyncTask<String,Bitmap,Bitmap>{
        @Override
        protected Bitmap doInBackground(String... params) {
            try {
                //2.获取URL对象
                URL url = new URL(params[0]);
                Log.d("GetNetPic","params[0] = " + params[0]);
                //3.获取连接对象
                final HttpURLConnection conn = (HttpURLConnection)url.openConnection();
                //4.初始化
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                conn.setReadTimeout(5000);
                conn.connect();
                //如果conn.getResponseCode()==200，则表示连接成功
                if(conn.getResponseCode() == 200){
                    Log.d("GetNetPic","OK");
                    //获取图片数据流
                    InputStream is = conn.getInputStream();
                    //BitmapFactory加工成Bitmap格式
                    Bitmap bitmap = BitmapFactory.decodeStream(is);
                    return bitmap;
                }else {
                    Log.d("GetNetPic","Not OK");
                }
            } catch (Exception e) {
                e.printStackTrace();

            }
            return null;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {

            super.onPostExecute(bitmap);
            if(bitmap == null){
                Toast.makeText(MainActivity.this,"获取失败...",Toast.LENGTH_SHORT).show();
            }else{
                imageView.setImageBitmap(bitmap);
            }
        }
    }