Android中使用ImageView控件显示网络图片

在android4.0以后的版本中,为了使得主界面流畅,所以设置了不允许在主线程中访问网络,为了安全,又不允许在其它线程中访问控件,这样就造成了ImageView等需要使用网络的控件更新时的问题,本文以Handler+Runnable的方式实现了ImageView控件显示网络图片.

在android4.0之后,如果在主线程中访问网络,会报一个android.os.networkonmainthreadexception的异常.因为在ui线程中访问网络的话,就要等待网络传输完成,期间就会阻塞线程,使界面卡住.

为了访问网络资源,可以开启一个线程,异步加载.但这个新线程又不具有更新控件的能力,所以就需要一个中间人来完成ui线程和网络线程的联系,本文使用的是消息机制,网络线程发送一个消息,ui线程中收到后执行相应工作.

packagecom.example.netimage;

 

importjava.io.InputStream;

importjava.net.HttpURLConnection;

importjava.net.URL;

 

importandroid.os.Bundle;

importandroid.os.Handler;

importandroid.os.Message;

importandroid.app.Activity;

importandroid.graphics.Bitmap;

importandroid.graphics.BitmapFactory;

importandroid.view.Menu;

importandroid.view.View;

importandroid.widget.Button;

importandroid.widget.EditText;

importandroid.widget.ImageView;

 

publicclass MainActivity extendsActivity {

     

    privateButton b;

    privateEditText et;

    publicImageView iv;

 

    @Override

    protectedvoid onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

         

        b = (Button)this.findViewById(R.id.button1);

        b.setOnClickListener(newButtonOnClickListener());

         

        iv = (ImageView)this.findViewById(R.id.imageView1);

        et = (EditText)this.findViewById(R.id.editText1);

    }

     

    privateHandler handler = newHandler() { 

        publicvoid handleMessage (Message msg) {// 此方法在ui线程运行 

            switch(msg.what) { 

            case1: 

                iv.setImageBitmap((Bitmap) msg.obj);// iv 显示从网络获取到的logo   

                break;  

            } 

        } 

    };

     

    classdownload implementsRunnable{

         

        @Override

        publicvoid run() {

            // TODO Auto-generated method stub

            String path = et.getText().toString();

            try{

                 

                //byte[] data = ImageService.getImage(path);

                URL url = newURL(path);

                HttpURLConnection con = (HttpURLConnection)url.openConnection();

                con.setConnectTimeout(5000);

                con.setRequestMethod("GET");

                con.connect();

                 

                if(con.getResponseCode() == 200){         

                    InputStream is = con.getInputStream();

                    //byte[] data = StreamTool.readStream(is);

                    Bitmap bitmap = BitmapFactory.decodeStream(is);//(data, 0, data.length);

                    handler.obtainMessage(1,bitmap).sendToTarget();

                }

                //Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);

                //ImageView iv = (ImageView)con.findViewById(R.id.imageView1);

            }catch(Exception e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

             

        }

    }

     

    privateclass ButtonOnClickListener implementsView.OnClickListener{

 

        @Override

        publicvoid onClick(View v) {

            // TODO Auto-generated method stub

            newThread(newdownload()).start();

        }

         

    }

 

    @Override

    publicboolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.

        getMenuInflater().inflate(R.menu.main, menu);

        returntrue;

    }

 

}