直接在UI線程中開啓子線程來更新TextView顯示的內容，運行程序我們會發現，如下錯 誤：android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.翻譯過來就是：只有創建這個控件的線程才能去更新該控件的內容。
所有的UI線程要去負責View的創建並且維護它，例如更新冒個TextView的顯示，都必須在主線程中去做，我們不能直接在UI線程中去創建子線程，要利用消息機制：handler，如下就是handler的簡單工作原理圖：
既然android給我們提供了Handler機制來解決這樣的問題，請看如下代碼：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
|
public
class
HandlerTestActivity extends
Activity { private
TextView tv; private
static
final
int
UPDATE = 0; private
Handler handler = new
Handler() { @Override public
void
handleMessage(Message msg) { //
TODO 接收消息並且去更新UI線程上的控件內容 if
(msg.what == UPDATE) { //
Bundle b = msg.getData(); //
tv.setText(b.getString("num")); tv.setText(String.valueOf(msg.obj)); } super.handleMessage(msg); } }; /**
Called when the activity is first created. */ @Override public
void
onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); tv
= (TextView) findViewById(R.id.tv); new
Thread() { @Override public
void
run() { //
TODO 子線程中通過handler發送消息給handler接收，由handler去更新TextView的值 try
{ for
(int
i = 0;
i < 100;
i++) { Thread.sleep(500); Message
msg = new
Message(); msg.what
= UPDATE; //
Bundle b = new Bundle(); //
b.putString("num", "更新後的值：" + i); //
msg.setData(b); msg.obj
= "更新後的值："
+ i; handler.sendMessage(msg); } } catch
(InterruptedException e) { e.printStackTrace(); } } }.start(); }} |