android中Handler、Thread、Runnable更新UI的思考

在寫一個小應用的時候，我接觸到了一個關於Handler和Thread以及runnable的問題，問了群裡各種人都解決不了，然後查閱大量資料，終於有些了解，現在發上來和大家分享。

主要是關於，Thread和Runnable的區別，以及他們在使用Handler時造成的影響~，我先上代碼

下面這個是錯誤的代碼~下面的代碼只要執行到handler中更新UI的部分就會報空指針錯誤~線程處用的Thread

public class MainActivity extends Activity {
	TextView text1, text2;
	Button button;
	myThread th;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		text1 = (TextView)findViewById(R.id.text1);
		text2 = (TextView)findViewById(R.id.text2);
		button = (Button)findViewById(R.id.button1);
		button.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				th = new myThread();
				th.start();
			}
		});
	}
	Handler myHandler = new Handler(){
		@Override
		public void handleMessage(Message msg) {
			// TODO Auto-generated method stub
			switch (msg.what) {
			case 1:
				System.out.println("-----------1--------------");
				System.out.println(msg.getData().getString("s1"));
				System.out.println(msg.getData().getString("s2"));
				try{
				 text1.setText(msg.getData().getString("s1"));
				 text2.setText(msg.getData().getString("s1"));
				}catch(Exception e){
					e.printStackTrace();
				}
				break;

			default:
				break;
			}
			super.handleMessage(msg);
		}
	};
}

class myThread extends Thread{
	String s1, s2;
	MainActivity ma = new MainActivity();
	public void run(){
		  s1 = "fsdfsgfdsgdfgfdgdhshshs";
		  s2 = "fsfsdgdshdhdshrehreherh";

		  
		  Message msg = new Message();
		  msg.what = 1;
		  Bundle bundle = new Bundle();
		  bundle.putString("s1", s1);
		  bundle.putString("s2", s2);
		  msg.setData(bundle);
		  ma.myHandler.sendMessage(msg);
	}
}

上面這段代碼，沒給注釋，但是很簡單，相信大家都能看懂~，這段代碼是錯誤的。

下面給大家上正確的代碼~線程處用的Runnable

public class MainActivity extends Activity {
	TextView text1, text2;
	Button button;
	Thread th;

	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		text1 = (TextView)findViewById(R.id.text1);
		text2 = (TextView)findViewById(R.id.text2);
		button = (Button)findViewById(R.id.button1);
		button.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				
				th = new Thread(runnable);
				th.start();
			}
		});
	}
	Handler myHandler = new Handler(){
		@Override
		public void handleMessage(Message msg) {
			// TODO Auto-generated method stub
			switch (msg.what) {
			case 1:
				System.out.println("-----------1--------------");
				System.out.println(msg.getData().getString("s1"));
				System.out.println(msg.getData().getString("s2"));
				try{
				 text1.setText(msg.getData().getString("s1"));
				 text2.setText(msg.getData().getString("s1"));
				}catch(Exception e){
					e.printStackTrace();
				}
				break;

			default:
				break;
			}
			super.handleMessage(msg);
		}
	};

	Runnable runnable = new Runnable() {
		@Override
		public void run() {
			// TODO Auto-generated method stub
		      String s1 = "fsdfsgfdsgdfgfdgdhshshs";
			  String s2 = "fsfsdgdshdhdshrehreherh";

			  Message msg = new Message();
			  msg.what = 1;
			  Bundle bundle = new Bundle();
			  bundle.putString("s1", s1);
			  bundle.putString("s2", s2);
			  msg.setData(bundle);
			  MainActivity.this.myHandler.sendMessage(msg);
		}
	};
}

這是正確的代碼，能正確更新UI。

找到問題以後，我又做了幾個小實驗，發現，其實用Thread也是可以的，也是可以更新UI的，就像這樣

public class MainActivity extends Activity {
	TextView text1, text2;
	Button button;
	myThread th;

	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		text1 = (TextView)findViewById(R.id.text1);
		text2 = (TextView)findViewById(R.id.text2);
		button = (Button)findViewById(R.id.button1);
		button.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				
				th = new myThread();
				th.start();
			}
		});
	}
	Handler myHandler = new Handler(){
		@Override
		public void handleMessage(Message msg) {
			// TODO Auto-generated method stub
			switch (msg.what) {
			case 1:
				System.out.println("-----------1--------------");
				System.out.println(msg.getData().getString("s1"));
				System.out.println(msg.getData().getString("s2"));
				try{
				 text1.setText(msg.getData().getString("s1"));
				 text2.setText(msg.getData().getString("s1"));
				}catch(Exception e){
					e.printStackTrace();
				}
				break;

			default:
				break;
			}
			super.handleMessage(msg);
		}
	};
	
	class myThread extends Thread{
		public void run() {
			// TODO Auto-generated method stub
		      String s1 = "fsdfsgfdsgdfgfdgdhshshs";
			  String s2 = "fsfsdgdshdhdshrehreherh";

			  Message msg = new Message();
			  msg.what = 1;
			  Bundle bundle = new Bundle();
			  bundle.putString("s1", s1);
			  bundle.putString("s2", s2);
			  msg.setData(bundle);
			  MainActivity.this.myHandler.sendMessage(msg);
	}
	}
}

到這，不知道大家發現問題在哪沒有？

據我所了解~Thread和Runnable的區別如下：

如果然一個線程實現Runnable接口，當調用這個線程對象開辟多線程時，可以讓這些線程調用同一變量~，（說白了就是，我主線程和拋出的子線程都可以用你主線程的變量了）

若這個線程類是繼承自Thread類而來，則通過內部類實現上述功能，利用的就是內部類可任意訪問外部類這一特性（這段說的就是我3段代碼的最後1段）。

好了，完了，就這麼多，希望對大家有幫助