Handler 在子线程工作

public class MainActivity extends AppCompatActivity {

    private Button mButton;

    private TextView textView;

    DownLoad mLoad;

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

        initview();

        initDownLoad();


    }

    private void initview() {
        mButton = (Button) findViewById(R.id.test_btn);
        textView = (TextView) findViewById(R.id.textview);

        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Message message = new Message();
                message.obj = "sql work";
                mLoad.mHandler.sendMessage(message);
            }
        });

    }

    private void initDownLoad() {

        mLoad = new DownLoad();
        new Thread(mLoad).start();
    }


    class DownLoad implements Runnable {

        private Handler mHandler;

        @Override
        public void run() {



            Log.d("123", Thread.currentThread().getName());

            try {
                Thread.sleep(5000);

                mHandler = new Handler() {

                    @Override
                    public void handleMessage(Message msg) {

                        Log.d("123", msg.obj.toString());
                        
                        //获得主线程发来的消息，进行耗时处理，比如sql操作
                    }
                };
            } catch (InterruptedException e) {
                e.printStackTrace();
            }


        }
    }


}

在这里又报错了：
java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

无法在未调用Looper.prepare（）的线程中创建handler.

通过看源码例子 实现以下代码

  public void run() {

            Looper.prepare();

            Log.d("123", Thread.currentThread().getName());

            try {
                Thread.sleep(5000);

                mHandler = new Handler() {

                    @Override
                    public void handleMessage(Message msg) {

                        Log.d("123", msg.obj.toString());
                    }
                };
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            Looper.loop();
        }
    }

这样就能正常使用了，到这里基础的用法就已经理解了，想要理解Handler还是需要看源码的，下篇再让我们从源码分析下Handler的使用

Handler源码浅析(一)
Handler总结