android-Handler Message

網路抓取圖片，或是讀很大量的資料，如果在主執行緒中超過五秒還沒完成的話
會收到android系統的錯誤強制關閉，這時候需要把這些耗時的工作放在一個子執行續上
因為子執行緒涉及到UI更新，為了避免避免多個子執行緒去更新發生錯誤
為了避免這種錯誤，更新UI只能在主執行緒更新
由於Handler運行在主執行緒中(UI執行緒中)，它與子執行緒可以通過Message對象來傳遞資料，

• 最近比較常用到順便紀錄一下!!

注意

如果要使用要在Handler使用startActivity的話
因為上下文的關係 要注意Context

 static Context mContext;
Intent intent = new Intent(mContext, InferenceActivity.class);
mContext.startActivity(intent);

Handler 範例

public class MainActivity extends AppCompatActivity {



	@InjectView(R.id.btn_update)
    Button mBtnUpdate;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_);
        ButterKnife.inject(this);
    }

    @OnClick({R.id.btn_update})
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn_update:
                 Login();
                break;
        }
    }

    private void Login() {
        Runnable run = new Runnable() {
            @Override
            public void run() {
                Message msg = new Message();

                     msg.what = 1000;
                }
                mHandler.sendMessage(msg);
            }
        };
        new Thread(run).start();
    }

    Handler mHandler = new Handler() {
        public void handleMessage(android.os.Message msg) {
            switch (msg.what) {
                case 1000:

                    break;
                case 1001:

                    break;

            }
        }
    };
}

Handler 範例二

MainActivity

public class MainActivity extends AppCompatActivity {

    @InjectView(R.id.btn_start)
    Button mBtnStart;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_);
        ButterKnife.inject(this);
    }

   @OnClick(R.id.btn_start)
    public void onClick(View view) {
     DateUpdate dateUpdate = new DateUpdate();
    }

    public Handler getHandler() {
        return this.mHandler;
    }
   Handler mHandler = new Handler() {
       public void handleMessage(android.os.Message msg) {

           switch (msg.what) {
               case 1000:
               //程式碼
                   break;
               case 1001:
             //程式碼
                   break;
           }
       }
   };
}

DateUpdate

public class DateUpdate {

    public DateUpdate() {

        Runnable run = new Runnable() {
            @Override
            public void run() {       
                Message msg = new Message();

                    if () {

                        msg.what = 1000;
                    } else {

                        msg.what = 1001;
                    }
                }
                mHandler.sendMessage(msg);
            }
        };
        new Thread(run).start();

    }

    StartSuccessActivity startSuccessActivity = new StartSuccessActivity();
    Handler mHandler = startSuccessActivity.getHandler();
}