很多情況先都需要開啟其他子線程，但子線程又不能直接更新主線的UI，利用handler可以實作這個需求
1、定義一個辨別DOWN_FINISH和new 一個handler并重寫handleMessage方法
2、在子線程中Message message=Message.obtain()；這樣比直接new一個Message效率更高，應為進度條是一直重新整理，會一直new，而obtain()方式的的解釋是A Message object from the global pool.
直接看代碼：
public class MainActivity extends Activity implements OnClickListener {
private Button download;
private Button pbBtn;
private EditText et;
private ProgressBar pb;
private static final int DOWN_FINISH = 3;
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case DOWN_FINISH:
pb.setVisibility(View.INVISIBLE);
Toast.makeText(MainActivity.this, "下載下傳完成", Toast.LENGTH_SHORT)
.show();
break;
default:
break;
}
};
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pbBtn = (Button) findViewById(R.id.button2);
pb = (ProgressBar) findViewById(R.id.progressBar1);
pb.setVisibility(View.INVISIBLE);
pbBtn.setOnClickListener(this);
}
public void tryLoad() {
new Thread(new Runnable() {
@Override
public void run() {
String url = et.getText().toString().trim();
String newFileName = url.substring(url.lastIndexOf("/") + 1,
url.length());
if (!TextUtils.isEmpty(url)) {
DownloadUtils.download(url, newFileName, "/sdcard/", 10);
}
}
}).start();
}
public void progressBar() {
pb.setVisibility(View.VISIBLE);
final int max = 20;
pb.setMax(max);
new Thread(new Runnable() {
int current = 0;
boolean flag = true;
@Override
public void run() {
while (flag) {
current++;
pb.setProgress(current);
try {
Thread.sleep(300);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if (current >= max) {
flag = false;
Message msg = Message.obtain(handler);
msg.what = DOWN_FINISH;
// 這裡是sendMessage方法，而不是自己重寫的handleMessage方法
handler.sendMessage(msg);
}
}
}
}).start();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (v == pbBtn) {
progressBar();
}
}
}
效果：
紅色區域是 進度條，因為我這初始化時讓其不可見，點選 PBTest 顯示進度條及進度動畫，進度達到最大值時讓其不可見
調用的方法是
pb.setVisibility(View.INVISIBLE);
View.VISIBLE
View.INVISIBLE
View.GONE//如果使用這個，其他控件的位置和這個控件不要有聯系，否則布局會會亂
