Android中子线程更新主线程UI和ProgressBar的应用

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很多情况先都需要开启其他子线程，但子线程又不能直接更新主线的UI，利用handler可以实现这个需求

1、定义一个标识DOWN_FINISH和new 一个handler并重写handleMessage方法

2、在子线程中Message message=Message.obtain()；这样比直接new一个Message效率更高，应为进度条是一直刷新，会一直new，而obtain()方式的的解释是A Message object from the global pool.

直接看代码：

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() {@Overridepublic void handleMessage(Message msg) {switch (msg.what) {case DOWN_FINISH:pb.setVisibility(View.INVISIBLE);Toast.makeText(MainActivity.this, "下载完成", Toast.LENGTH_SHORT).show();break;default:break;}};};@Overrideprotected 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() {@Overridepublic 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;@Overridepublic void run() {while (flag) {current++;pb.setProgress(current);try {Thread.sleep(300);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}if (current >= max) {flag = false;Message msg = Message.obtain(handler);msg.what = DOWN_FINISH;// 这里是sendMessage方法，而不是自己重写的handleMessage方法handler.sendMessage(msg);}}}}).start();}@Overridepublic 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;}@Overridepublic void onClick(View v) {// TODO Auto-generated method stubif (v == pbBtn) {progressBar();}}}

效果：

红色区域是进度条，因为我这初始化时让其不可见，点击 PBTest 显示进度条及进度动画，进度达到最大值时让其不可见

调用的方法是

pb.setVisibility(View.INVISIBLE);

View.VISIBLE

View.INVISIBLE

View.GONE//如果使用这个，其他控件的位置和这个控件不要有联系，否则布局会会乱