Handler

private ImageView image_main;
    private Handler handler =new Handler() {
        @Override
        public void handleMessage(Message msg) {
           //处理其他线程传递过来的消息。
           Bitmap bitmap = (Bitmap) msg.obj;
            image_main.setImageBitmap(bitmap);
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        image_main = (ImageView) findViewById(R.id.image_main);
        //开启一个线程下载图片。
        startThead();
    }

    private void startThead() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                //执行在工作线程中。
                String path = "http://img4.duitang.com/uploads/item/201306/20/20130620221932_FVnZK.thumb.600_0.jpeg";
                try {
                    URL url = new URL(path);
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.connect();
                    ;
                    int code = conn.getResponseCode();
                    if (code == 200) {
                        InputStream is = conn.getInputStream();
                        Bitmap bitmap = BitmapFactory.decodeStream(is);
                        //将图片设置给ImageView.
                        //发送消息
                        Message msg = new Message();
                        //arg1,arg2--放的都是整数。 what---类型。也是整数。obj---放的是任意的对象
                        msg.obj = bitmap;
                        handler.sendMessage(msg);//发送消息。
                    }
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

private ViewPager vg_main;
private List<ImageView> list;
private int[] imags_id = {R.mipmap.a,R.mipmap.b,R.mipmap.c,R.mipmap.d,R.mipmap.e};
int position = 0;
private Handler handler = new Handler(){
    @Override
    public void handleMessage(Message msg) {

        //定位
        vg_main.setCurrentItem(++position,true);
    }
};
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    vg_main  = (ViewPager) findViewById(R.id.viewpager);
    initList();
    MyPagerAdapter adapter = new MyPagerAdapter();
    vg_main.setAdapter(adapter);
    new Thread(new Runnable() {
        @Override
        public void run() {
            //发送消息到主线程。
            while(true) {
                handler.sendEmptyMessage(1);
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }).start();
}

private void initList() {
    list = new ArrayList<ImageView>();
   for(int i=0;i<imags_id.length;i++){
       ImageView img = new ImageView(this);
       img.setImageResource(imags_id[i]);
       list.add(img);
   }
}
class MyPagerAdapter extends PagerAdapter{

    @Override
    public int getCount() {
        return Integer.MAX_VALUE;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view==object;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        container.addView(list.get(position%list.size()));
        return list.get(position%list.size());
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        container.removeView(list.get(position%list.size()));
    }
}

private TextView tv_msg;
private Handler handler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
       String str = (String) msg.obj;
        tv_msg.setText(str);
    }
};
private Handler handler_work;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    tv_msg = (TextView) findViewById(R.id.tv_message);
}
public void click(View view){
    switch (view.getId()){
        case R.id.btn_main:
            //Ui线程向工作线程发送数据。
            Message msg = handler_work.obtainMessage();
            msg.obj = "我是main线程发送过来的消息";
            handler_work.sendMessage(msg);
            break;
        case R.id.btn_workThread:
            new Thread(new Runnable() {
                @Override
                public void run() {
                    Message msg = handler.obtainMessage();
                    msg.obj = "我是工作线程发送过来的消息";
                    handler.sendMessage(msg);
                    //创建handler
                    handler_work = new Handler(){
                        @Override
                        public void handleMessage(Message msg) {
                           String text = (String) msg.obj;
                            Log.i("work",text);
                        }
                    };
                }
            }).start();
            break;
    }
}

private Button btn_start;
private TextView tv_time,tv_stop;
private int total = 10;
private Handler handler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
        //设置
        int timer = msg.arg1;
       tv_time.setText(msg.arg1 + "");

        if(timer==0){
            btn_start.setEnabled(true);
            tv_stop.setVisibility(View.VISIBLE);
        }

    }
};

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

private void initView() {
    btn_start = (Button) findViewById(R.id.btn_start);
    tv_time = (TextView) findViewById(R.id.tv_time);
    tv_stop = (TextView) findViewById(R.id.tv_stop);
}

public void click(View view){
    //按钮不再可用。
    btn_start.setEnabled(false);
    tv_stop.setVisibility(View.INVISIBLE);
    //改变tv_time时间。
    new Thread(new Runnable() {
        @Override
        public void run() {
            int total = 10;
            //马上设置。
            Message msg = handler.obtainMessage();
            msg.arg1 = total;
            handler.sendMessage(msg);
            for(int i=9;i>=0;i--){
                Message msg2 = handler.obtainMessage();
               msg2.arg1 = i;
             handler.sendMessage(msg2);
                Log.i("Main",msg2.arg1+"");
                // 睡眠。

                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }).start();
}