Android 程式开发：（十二）最基本的UI控件 —— 12.3ProgressBar

当执行某些正在处理的任务时，ProgressBar提供了一个可视化的反馈。例如，你在从web服务器下载数据，然后需要更新下载的状态。在这种情况下，ProgressBar就是一个很好的选择。下面的例子，展示如何去使用ProgressBar。

1、创建一个工程，BasicViews2。

2、main.xml中的代码。

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

<ProgressBarandroid:id="@+id/progressbar"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>

LinearLayout>

3、Basic2Activity.java中的代码。

package net.learn2develop.BasicViews2;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.ProgressBar;

public class BasicViews2Activityextends Activity {
    static int progress;
    ProgressBar progressBar;
    int progressStatus = 0;
    Handler handler = new Handler();

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        progress = 0;
        progressBar = (ProgressBar) findViewById(R.id.progressbar);

        //---do some work in background thread---
        new Thread(new Runnable()
        {
            public  void run()
            {
                //?do some work here?
                while (progressStatus <10)
                {
                    progressStatus = doSomeWork();

                }

                //---hides the progress bar---
                handler.post(new Runnable()
                {
                    publicvoid run()
                    {
                        //---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE---
                        progressBar.setVisibility(View.GONE);
                    }
                });
            }

            //---do some long running work here---
            private int doSomeWork()
            {
                try {
                    //---simulate doing some work---
                    Thread.sleep(500);
                } catch (InterruptedException e)
                {
                    e.printStackTrace();
                }
                return ++progress;
            }
        }).start();
    }
}

package net.learn2develop.BasicViews2; import android.app.Activity; import android.os.Bundle; import android.os.Handler; import android.view.View; import android.widget.ProgressBar; public class BasicViews2Activity extends Activity { static int progress; ProgressBar progressBar; int progressStatus = 0; Handler handler = new Handler(); /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); progress = 0; progressBar = (ProgressBar) findViewById(R.id.progressbar); //---do some work in background thread--- new Thread(new Runnable() { public void run() { //?do some work here? while (progressStatus < 10) { progressStatus = doSomeWork(); } //---hides the progress bar--- handler.post(new Runnable() { public void run() { //---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE--- progressBar.setVisibility(View.GONE); } }); } //---do some long running work here--- private int doSomeWork() { try { //---simulate doing some work--- Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } return ++progress; } }).start(); } }4、F11调试，会看见ProgressBar的动画，5秒之后，动画消失。

接下来展示如何自定义ProgressBar的样式。

1、使用之前的例子，修改main.xml。

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

<ProgressBarandroid:id="@+id/progressbar"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    style="@android:style/Widget.ProgressBar.Horizontal"/>

LinearLayout>

2、Basic2Activity.java中的代码。

package net.learn2develop.BasicViews2;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.ProgressBar;

public class BasicViews2Activityextends Activity {
    static int progress;
    ProgressBar progressBar;
    int progressStatus = 0;
    Handler handler = new Handler();

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        progress = 0;
        progressBar = (ProgressBar) findViewById(R.id.progressbar);
        progressBar.setMax(200);

        //---do some work in background thread---
        new Thread(new Runnable()
        {
            public void run()
            {
                //?do some work here?
                while (progressStatus <100)
                {
                    progressStatus = doSomeWork();

                    //?Update the progress bar?
                    handler.post(new Runnable()
                    {
                        public  void run() {
                            progressBar.setProgress(progressStatus);
                        }
                    });
                }

                //---hides the progress bar---
                handler.post(new Runnable()
                {
                    publicvoid run()
                    {
                        //---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE---
                        progressBar.setVisibility(View.GONE);
                    }
                });
            }

            //---do some long running work here---
            private int doSomeWork()
            {
                try {
                    //---simulate doing some work---
                    Thread.sleep(50);
                } catch (InterruptedException e)
                {
                    e.printStackTrace();
                }
                return ++progress;
            }
        }).start();
    }
}

package net.learn2develop.BasicViews2; import android.app.Activity; import android.os.Bundle; import android.os.Handler; import android.view.View; import android.widget.ProgressBar; public class BasicViews2Activity extends Activity { static int progress; ProgressBar progressBar; int progressStatus = 0; Handler handler = new Handler(); /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); progress = 0; progressBar = (ProgressBar) findViewById(R.id.progressbar); progressBar.setMax(200); //---do some work in background thread--- new Thread(new Runnable() { public void run() { //?do some work here? while (progressStatus < 100) { progressStatus = doSomeWork(); //?Update the progress bar? handler.post(new Runnable() { public void run() { progressBar.setProgress(progressStatus); } }); } //---hides the progress bar--- handler.post(new Runnable() { public void run() { //---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE--- progressBar.setVisibility(View.GONE); } }); } //---do some long running work here--- private int doSomeWork() { try { //---simulate doing some work--- Thread.sleep(50); } catch (InterruptedException e) { e.printStackTrace(); } return ++progress; } }).start(); } }3、F11调试。

4、当ProgressBar的进度到达50%的时候，它就会消失。

附：

ProgressBar的样式列表。

• Widget.ProgressBar.Horizontal
• Widget.ProgressBar.Small
• Widget.ProgressBar.Large
• Widget.ProgressBar.Inverse
  
• Widget.ProgressBar.Small.Inverse
• Widget.ProgressBar.Large.Inverse