2008年大学生就业形势

说到ProgressDialog和ProgressBar,相信大家不陌生吧，就是比如导入联系人的时候会出现一个进度条的控件，或者下载的时候的进度条。
首先说一下ProgressBar:
既然要更新UI，在android中，一般是不在主线程也就是Activity所在的那个线程来做些费时的操作的，因为这样会阻塞主线程，导致出现ANR错误。因此，一般是新开一个线程来做费时的操作，当然，做操作的时候又要通知前端的主线程来更新界面，这样能让用户知道在做操作啊，因此，就需要使用android中的线程通信Handler了。好了。下面是示例：
1，写好一个带progressbar的xml布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">

<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
<ProgressBar
android:id="@+id/rectangleProgressBar"
style="?android:attr/progressBarStyleHorizontal" mce_style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:visibility="gone"
/>
<ProgressBar
android:id="@+id/circleProgressBar"
style="?android:attr/progressBarStyleLarge" mce_style="?android:attr/progressBarStyleLarge"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:visibility="gone"
/>

<Button android:id="@+id/button"
android:text="Show ProgressBar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</LinearLayout>

2，Activity代码：

public class ProgressBarDemo extends Activity {

private ProgressBar rectangleProgressBar,circleProgressBar;
private Button mButton;

protected static final int STOP = 0x10000;
protected static final int NEXT = 0x10001;
private int iCount = 0;

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//findView By id
rectangleProgressBar = (ProgressBar)findViewById(R.id.rectangleProgressBar);
circleProgressBar = (ProgressBar)findViewById(R.id.circleProgressBar);
mButton = (Button)findViewById(R.id.button);

rectangleProgressBar.setIndeterminate(false);
circleProgressBar.setIndeterminate(false);

mButton.setOnClickListener(new Button.OnClickListener() {

public void onClick(View v) {

rectangleProgressBar.setVisibility(View.VISIBLE);
circleProgressBar.setVisibility(View.VISIBLE);

rectangleProgressBar.setMax(100);
rectangleProgressBar.setProgress(0);
circleProgressBar.setProgress(0);

//创建一个线程,每秒步长为5增加,到100%时停止
Thread mThread = new Thread(new Runnable() {

public void run() {

for(int i=0 ; i < 20; i++){
try{
iCount = (i + 1) * 5;
Thread.sleep(1000);
if(i == 19){
Message msg = new Message();
msg.what = STOP;
mHandler.sendMessage(msg);
break;
}else{
Message msg = new Message();
msg.what = NEXT;
mHandler.sendMessage(msg);
}
}catch (Exception e) {
e.printStackTrace();
}
}

}
});
mThread.start();
}
});
}

//定义一个Handler
private Handler mHandler = new Handler(){
public void handleMessage(Message msg){
switch (msg.what) {
case STOP:
rectangleProgressBar.setVisibility(View.GONE);
circleProgressBar.setVisibility(View.GONE);
Thread.currentThread().interrupt();
break;
case NEXT:
if(!Thread.currentThread().isInterrupted()){
rectangleProgressBar.setProgress(iCount);
circleProgressBar.setProgress(iCount);
}
break;
}
}
};
}

当然，这里涉及两种progressbar，一种是进度条的，一种是环形的，另外这里的线程停止方式，还可以有另外的方式，就是设置一个boolean变量来控制线程的停止。

再说一下ProgressDialog的用法；示例代码：
1，也是先看布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView android:id="@+id/status"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello"
/>
<Button android:id="@+id/beginBtn"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="begin"
/>
</LinearLayout>

2，再看Activity代码：

public class ProgressBarDemo extends Activity {

private TextView statusTextView;
private Button beginBtn;
private ProgressDialog progressDialog;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
statusTextView = (TextView)findViewById(R.id.status);
beginBtn = (Button)findViewById(R.id.beginBtn);
setListener();
}

/**
* 用Handler来更新UI
*/
private Handler handler = new Handler(){

@Override
public void handleMessage(Message msg) {

//关闭ProgressDialog
progressDialog.dismiss();

//更新UI
statusTextView.setText("Completed!");
}};

/**
* 点击按钮事件listener
*/
private void setListener(){
beginBtn.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {

//显示ProgressDialog
progressDialog = ProgressDialog.show(ProgressBarDemo.this, "Loading...", "Please wait...", true, false);

//新建线程
new Thread(){

@Override
public void run() {
//需要花时间计算的方法
Calculation.calculate(4);

//向handler发消息
handler.sendEmptyMessage(0);
}}.start();
}
});
}

class Calculation {

public static void calculate(int sleepSeconds){
try {
Thread.sleep(sleepSeconds * 1000);
} catch (Exception e) {
// TODO: handle exception
}
}

}

}

很简单吧，主要使用的android中线程之间的通信机制Handler。