AsyncTask的异步线程的使用

public class MainActivity extends AppCompatActivity {
    public Context context;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent();
                intent.setClass(MainActivity.this,ImageText.class);
                startActivity(intent);
            }
        });
        Button button1= (Button) findViewById(R.id.button2);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent();
                intent.setClass(MainActivity.this,ProgressBarTest.class);
                startActivity(intent);
            }
        });
    }

}

public class ImageText extends AppCompatActivity {
    private ImageView imageView;
    private ProgressBar progressBar;
    private static String URL="http://img.my.csdn.net/uploads/201504/12/1428806103_9476.png";
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.imagetest);
        imageView=(ImageView) findViewById(R.id.image11);
        progressBar= (ProgressBar) findViewById(R.id.bar);
        new MyASyncTask().execute(URL);
    }
    class MyASyncTask extends AsyncTask<String,Void,Bitmap> {
        @Override
        protected void onPostExecute(Bitmap bitmap) {
            //在已经加载过图片后Progressbar设置为不可见
            progressBar.setVisibility(View.GONE);
            //设置已经传入的网络图片bitmap
            imageView.setImageBitmap(bitmap);
            super.onPostExecute(bitmap);
        }

        @Override
        protected void onPreExecute() {
            //显示进度条
            progressBar.setVisibility(View.VISIBLE);
            super.onPreExecute();
        }

        @Override
        protected Bitmap doInBackground(String... strings) {
            //从excute中获得所传进来的string的值
            String url=strings[0];
            //必须初始化bitmap
            Bitmap bitmap = null;
            //设置网络连接的对象
            URLConnection connection;
            //设置输入流
            InputStream inputStream;
            try {
                //获取网络连接对象,必须导入java.net.URL的包
                connection=new URL(url).openConnection();
                inputStream=connection.getInputStream();
                Thread.sleep(3000);
                //封装输入流
                BufferedInputStream bis=new BufferedInputStream(inputStream);
                //解析输入流
                bitmap= BitmapFactory.decodeStream(bis);
                //关闭输入流和封装流
                inputStream.close();
                bis.close();
            } catch (IOException | InterruptedException e) {
                e.printStackTrace();
            }
            //返回所接受过的bitmap
            return bitmap;
        }
    }
    }

public class ProgressBarTest extends AppCompatActivity {
    private MaysncTask mTask;
    private ProgressBar progressBar;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.progressbartest);
        //获取自定义内部类的AsyncTask的方法
        mTask=new MaysncTask();
        //运行这个方法
        mTask.execute();
        progressBar= (ProgressBar) findViewById(R.id.progressBar);
    }

    @Override
    //在activity退出前想保存用户重要数据的,必须在onPause中处理,因为当系统急需内存事,onStop和onDestroy是不会被执行的,
    protected void onPause() {
        super.onPause();
        if(mTask!=null&&mTask.getStatus()==AsyncTask.Status.RUNNING){
            mTask.cancel(true);
        }
    }

    class MaysncTask extends AsyncTask<Void,Integer,Void>{
        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
            //从doingbackground中得到所传入的值，为传入的整形数组values的第一个值，使用setprogress方法设置Progressbar的方法
            progressBar.setProgress(values[0]);
            if(isCancelled()){
                //判断AsyncTask是否为cancel状态如果为cancel状态则return。return语句是将函数的值返回主调函数
                return;
            }
        }

        @Override
        protected Void doInBackground(Void... voids) {
            for(int i=0;i<100;i++){
                if(isCancelled()){
                    break;
                }
                //publishProgress() 更新进度，给onProgressUpdate()传递进度参数publishProgress传递的为整数
                publishProgress(i);
                try {
                    //设置延迟的效果300毫秒
                    Thread.sleep(300);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            return null;
        }
    }
    }