消息机制相关API

Message(消息)

可理解为线程之间通讯的数据单元, 可以通过message携带需要的数据

创建对象: Message.obtain(what)

封装数据

public int what

public int arg

public Object obj

Handler(处理器)

Handler是Message的处理器, 同时也负责消息的发送和移除的工作

发送即时消息(马上发送, 马上处理): sendMessage(Message msg)

发送延迟消息(马上发送, 延迟处理): sendMessageDelayed(Message ms, long time)

处理消息: handleMessage(Message msg) (回调方法)

移除还没处理的消息(延迟消息还没被处理前, 可以继续移除): removeMessage(int what)

MessageQueue(消息队列)  

用来存储通过Handler发送的消息

他是一个按Message的when排序的优先级队列(队列的特点是先进先出, 但是这里是按照优先级来排的)

Looper(钩子) 循环器

负责循环取出Message Queue 里面的当前需要处理的Message

交给对应的Handler进行处理

处理完后,将Message缓存到消息池中, 已备服用

测试用例

需求说明

1. 点击GET请求获取, 显示提示正在加载的进度条, 分线程请求网络

2. 得到数据后, 将数据显示到输入框中, 同时隐藏进度条

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <ProgressBar
        android:id="@+id/pb_handler1_loading"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal" 
        android:visibility="invisible"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="getSubmit1"
        android:text="GET Submit" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="getSubmit2"
        android:text="GET Submit2" />

    <EditText
        android:id="@+id/et_handler1_result"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="显示结果" >
    </EditText>
</LinearLayout>

测试无Handler的基本使用

1. 主线程, 显示提示视图(ProgressDialog/ProgressBar)

2. 分线程, 联网请求, 并得到响应数据

3. 主线程, 显示数据/隐藏提示视图

public class HandlerTestActivity extends Activity {

	private ProgressBar pb_handler1_loading;
	private EditText et_handler1_result;

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

		pb_handler1_loading = (ProgressBar) findViewById(R.id.pb_handler1_loading);
		et_handler1_result = (EditText) findViewById(R.id.et_handler1_result);
	}

	
	public void getSubmit(View v) {
		//1. 主线程, 显示提示视图(ProgressDialog/ProgressBar)
		pb_handler1_loading.setVisibility(View.VISIBLE);
		//2. 分线程, 联网请求, 并得到响应数据
		new Thread(){
			public void run() {
				String path = "http://192.168.10.165:8080/Web_Server/index.jsp?name=Tom&age=12";
				try {
					final String result = requestToString(path);
					
					//3. 主线程, 显示数据
					runOnUiThread(new Runnable() {
						@Override
						public void run() {
							et_handler1_result.setText(result);
							pb_handler1_loading.setVisibility(View.INVISIBLE);
						}
					});
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}.start();
	}
	
	/**
	 * 请求服务器端, 得到返回的结果字符串
	 * @param path  : http://192.168.30.165:8080/Web_server/index.jsp?username=tom&age=12
	 * @return
	 * @throws Exception
	 */
	public String requestToString(String path) throws Exception {
		URL url = new URL(path);
		HttpURLConnection connection = (HttpURLConnection) url.openConnection();
		connection.setConnectTimeout(5000);
		connection.setReadTimeout(5000);
		connection.connect();
		InputStream is = connection.getInputStream();
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		byte[] buffer = new byte[1024];
		int len = -1;
		while ((len = is.read(buffer)) != -1) {
		baos.write(buffer, 0, len);
		}
		baos.close();
		is.close();
		String result = baos.toString();
		connection.disconnect();
	
		return result;
	}
}

测试有Handler的基本使用

1. 创建Handler成员变量对象, 并重写其handleMessage()
2. 在分/主线程创建Message对象
3. 使用handler对象发送Message
4. 在handleMessage()中处理消息

public class HandlerTestActivity extends Activity {

	private ProgressBar pb_handler1_loading;
	private EditText et_handler1_result;

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

		pb_handler1_loading = (ProgressBar) findViewById(R.id.pb_handler1_loading);
		et_handler1_result = (EditText) findViewById(R.id.et_handler1_result);
	}

	//1. 创建Handler成员变量对象, 并重写其handleMessage()
	private Handler handler = new Handler(){
		public void handleMessage(android.os.Message msg) { //在主线程执行
			if(msg.what == 1) {
				//4. 在handleMessage()中处理消息
				String result = (String) msg.obj;
				et_handler1_result.setText(result);
				pb_handler1_loading.setVisibility(View.INVISIBLE);
			}
		}
	};


	public void getSubmit(View v) {
		//1). 主线程, 显示提示视图(ProgressDialog/ProgressBar)
		pb_handler1_loading.setVisibility(View.VISIBLE);
		//2). 分线程, 联网请求, 并得到响应数据
		new Thread(){
			public void run() {
				String path = "http://192.168.10.165:8080/Web_Server/index.jsp?name=Tom&age=12";
				try {
					String result = requestToString(path);

					//3). 主线程, 显示数据
					//2. 在分/主线程创建Message对象
					Message message = Message.obtain();
					message.what = 1;//标识
					message.obj = result;
					//3. 使用handler对象发送Message
					handler.sendMessage(message);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}.start();
	}
	
	/**
	 * 请求服务器端, 得到返回的结果字符串
	 * @param path  : http://192.168.30.165:8080/Web_server/index.jsp?username=tom&age=12
	 * @return
	 * @throws Exception
	 */
	public String requestToString(String path) throws Exception {
		URL url = new URL(path);
		HttpURLConnection connection = (HttpURLConnection) url.openConnection();
		connection.setConnectTimeout(5000);
		connection.setReadTimeout(5000);
		connection.connect();
		InputStream is = connection.getInputStream();
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		byte[] buffer = new byte[1024];
		int len = -1;
		while ((len = is.read(buffer)) != -1) {
		baos.write(buffer, 0, len);
		}
		baos.close();
		is.close();
		String result = baos.toString();
		connection.disconnect();
	
		return result;
	}

}

应用DEMO

消息机制原理