设备分为两种：字符设备和块设备。不同之处在于块设备对于请求有缓冲区，因此它们可以选择以什么顺序进行响应。对于存储设备而言这一点是很重要的,因为在读写连续的扇区时比远远的分离的扇区更快。另一个不同就是块设备只能以块为单位接受输入和返回输出（块的大小根据设备的不同而不同），而字符设备只能使用它们可能使用的或多或少的字节大小。大多数设备是字符设备，因为它们不需要这种缓冲而且不以固定块大小进行操作。你可以用ls -l区分一个设备文件是块设备还是字符设备.如果开头是“b”，那么它就是块设备；如果是“c”，那么就是字符设备。

package org.pskink;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Matrix;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.Transformation;
import android.widget.AdapterView;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.AdapterView.OnItemSelectedListener;

public class AnimatedSizingGallery extends Gallery implements OnItemSelectedListener {
	public static final String TAG = "AnimatedSizingGallery";
	private static final int MSG_ZOOM_IN = 1;
	private  static final long DELAY = 100;

	private View mPrev;
	private float mAnimationScale;
	private float mAnimationOffsetY;
	private int mAnimationDuration;
	
	public AnimatedSizingGallery(Context context, AttributeSet attrs) {
		super(context, attrs);
		TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.AnimatedSizingGallery);
		mAnimationScale = a.getFloat(R.styleable.AnimatedSizingGallery_animationScale, 2);
		mAnimationOffsetY = a.getFloat(R.styleable.AnimatedSizingGallery_animationOffsetY, 0);
		mAnimationDuration = a.getInteger(R.styleable.AnimatedSizingGallery_animationDuration, 500);
		a.recycle();
		setOnItemSelectedListener(this);
	}

	public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
		if (mPrev != null) {
			zoomOut();
		}
		mPrev = view;
		mGalleryHandler.removeCallbacksAndMessages(view);
		Message msg = Message.obtain(mGalleryHandler, MSG_ZOOM_IN, view);
		mGalleryHandler.sendMessageDelayed(msg, DELAY);
	}

	public void onNothingSelected(AdapterView<?> parent) {
		Log.d(TAG, "onNothingSelected called !!!");
		if (mPrev != null) {
			zoomOut();
			mPrev = null;
		}
	}
	
	private void zoomOut() {
		if (mGalleryHandler.hasMessages(MSG_ZOOM_IN, mPrev)) {
			mGalleryHandler.removeCallbacksAndMessages(mPrev);
		} else {
			ZoomAnimation a = (ZoomAnimation) mPrev.getAnimation();
			a.resetForZoomOut();
			mPrev.startAnimation(a);
		}
	}

	Handler mGalleryHandler = new Handler() {
		@Override
		public void dispatchMessage(Message msg) {
			if (msg.what == MSG_ZOOM_IN) {
				ImageView view = (ImageView) msg.obj;
				Animation a = new ZoomAnimation(view, 1, mAnimationScale, mAnimationOffsetY, mAnimationDuration);
				view.startAnimation(a);
			}
		}
	};

	class ZoomAnimation extends Animation {
		private float mFrom;
		private float mTo;
		private float mOffsetY;
		private int mPivotX;
		private int mPivotY;
		private float mInterpolatedTime;

		public ZoomAnimation(View v, float from, float to, float offsetY, int duration) {
			super();
			mFrom = from;
			mTo = to;
			mOffsetY = offsetY * v.getHeight();
			setDuration(duration);
			setFillAfter(true);
			mPivotX = v.getWidth() / 2;
			mPivotY = v.getHeight() / 2;
		}
		
		public void resetForZoomOut() {
			reset();
			mOffsetY = 0;
			mFrom = mFrom + (mTo - mFrom) * mInterpolatedTime;
			mTo = 1;
		}

		@Override
		protected void applyTransformation(float interpolatedTime, Transformation t) {
			mInterpolatedTime = interpolatedTime;
	        float s = mFrom + (mTo - mFrom) * interpolatedTime;
	        Matrix matrix = t.getMatrix();
	        if (mOffsetY != 0) {
	        	matrix.preTranslate(0, mOffsetY * interpolatedTime);
	        }
	        if (mTo == 1) {
	        	matrix.preRotate(360 * interpolatedTime, mPivotX, mPivotY);
	        }
            matrix.preScale(s, s, mPivotX, mPivotY);
		}
	}
}

通过Window-based Application创建项目(二)

操作过程：

（1）创建Window-based Application项目；

（2）新建UIViewController类文件（带有XIB）；

（3）在新建的UIViewController类的XIB上添加一个按钮；

（4）修改主文件类文件（.h 和 .m）

（5）编辑主文件类的XIB文件（增加一个UIViewController控件，同时属性nib和Class指向上面新建的UIViewController类）；

第1步：创建Window-based Application项目；

这里示例项目取名为 WinBasedApp2

第2步：新建UIViewController类文件（带有XIB）；

鼠标选中项目  WinBasedApp2  下的 Classes 目录，然后点鼠标右键：

显示下图窗口：

注意：选中 With XIB for user interface

这里示例取名为  FirstViewController  

将在Classes目录中新出现的文件 FirstViewController.xib  拖到Resources目录下。 

第3步： FirstViewController.xib 添加一个按钮。

打开 FirstViewController.xib 文件并在界面上增加一个按钮，按钮标题为 first view.

第4步：修改主文件类文件

WinBasedApp2AppDelegate.h

#import <UIKit/UIKit.h>

@class FirstViewController;

@interface WinBasedApp2AppDelegate : NSObject <UIApplicationDelegate> {

    UIWindow *window;

FirstViewController *viewController;

}

@property (nonatomic, retain) IBOutlet UIWindow *window;

@property (nonatomic, retain) IBOutlet FirstViewController *viewController;

@end

WinBasedApp2AppDelegate.m

#import "WinBasedApp2AppDelegate.h"

#import "FirstViewController.h"

@implementation WinBasedApp2AppDelegate

@synthesize window;

@synthesize viewController;

#pragma mark -

#pragma mark Application lifecycle

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {   

    // Override point for customization after application launch.

    [self.window addSubview:viewController.view];

    [self.window makeKeyAndVisible];

    return YES;

}

- (void)applicationWillResignActive:(UIApplication *)application {

    /*

     Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.

     Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.

     */

}

- (void)applicationDidEnterBackground:(UIApplication *)application {

    /*

     Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.

     If your application supports background execution, called instead of applicationWillTerminate: when the user quits.

     */

}

- (void)applicationWillEnterForeground:(UIApplication *)application {

    /*

     Called as part of  transition from the background to the inactive state: here you can undo many of the changes made on entering the background.

     */

}

- (void)applicationDidBecomeActive:(UIApplication *)application {

    /*

     Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.

     */

}

- (void)applicationWillTerminate:(UIApplication *)application {

    /*

     Called when the application is about to terminate.

     See also applicationDidEnterBackground:.

     */

}

#pragma mark -

#pragma mark Memory management

- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application {

    /*

     Free up as much memory as possible by purging cached data objects that can be recreated (or reloaded from disk) later.

     */

}

- (void)dealloc {

[viewController release];

    [window release];

    [super dealloc];

}

@end

第5步：编辑主文件类的XIB文件（ MainWindow.xib ）。

增加一个UIViewController控件，同时属性nib和Class指向上面新建的UIViewController类。

打开 MainWindow.xib   ，在Interface Builder中的Library中找到控件ViewController，然后将该控件拖到MainWindow.xib  的界面窗口中。 

打开Inspector （Interface Builder > Tools > Inspector），选中刚加的ViewController控件，然后在Inspector的Identity窗口中，设置Class属性为 FirstViewController

切换到Inspector的Attributes窗口，设置NIB Name属性为 FirstViewController

备注：以上操作的时候，注意保存。

运行后，显示结果如下图：