直接在UI线程中开启子线程来更新TextView显示的内容,运行程序我们会发现,如下错 误:android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.翻译过来就是:只有创建这个控件的线程才能去更新该控件的内容。
所有的UI线程要去负责View的创建并且维护它,例如更新冒个TextView的显示,都必须在主线程中去做,我们不能直接在UI线程中去创建子线程,要利用消息机制:handler,如下就是handler的简单工作原理图:
既然android给我们提供了Handler机制来解决这样的问题,请看如下代码:
01
public
class
HandlerTestActivity
extends
Activity {
03
private
static
final
int
UPDATE =
0
;
04
private
Handler handler =
new
Handler() {
07
public
void
handleMessage(Message msg) {
09
if
(msg.what == UPDATE) {
12
tv.setText(String.valueOf(msg.obj));
14
super
.handleMessage(msg);
18
/** Called when the activity is first created. */
20
public
void
onCreate(Bundle savedInstanceState) {
21
super
.onCreate(savedInstanceState);
22
setContentView(R.layout.main);
23
tv = (TextView) findViewById(R.id.tv);
30
for
(
int
i =
0
; i <
100
; i++) {
32
Message msg =
new
Message();
38
handler.sendMessage(msg);
40
}
catch
(InterruptedException e) {
我们就通过Handler机制来处理了子线程去更新UI线程控件问题,Andrid开发中要经常用到这种机制。