UIScrollView的用法(不定期更新)

先從最基本的研究起，用一個例子來說明，如何建立一個UIScrollView。

在xcode建立一個基於視圖的工程，然後開啟項目裡viewController的xib檔案，在view裡添加一個uiscrollview,然後安一定間距拖幾個button、textfield之類的到scrollview

裡，這樣ui基本的架構就完成了。

下面就是代碼部分了：

UIScrollViewDemoViewController.h

#import <UIKit/UIKit.h>@interface UIScrollViewDemoViewController : UIViewController<UITextFieldDelegate,UIScrollViewDelegate> {    IBOutlet UIScrollView * myScrollView;    UITextField * activeField;    CGFloat oldContentOffsetValue;    IBOutlet UITextField * textFieldOne;    IBOutlet UITextField * textFieldTwo;    IBOutlet UITextField * textFieldThree;    IBOutlet UITextField * textFieldFour;    BOOL keyboardShown;    BOOL isNeedSetOffset;    }@property (nonatomic,retain) UITextField * activeField;@end

上面代碼裡，我xib檔案建立了五個iboutlet變數，分別是四個textfield和一個scrollview,然後就可以到xib檔案裡，把它們和對應的ui相串連趕來。

其它的變數在實現檔案裡會用到。

UIScrollViewDemoViewController.m

#import "UIScrollViewDemoViewController.h"@implementation UIScrollViewDemoViewController@synthesize activeField;- (void)dealloc{    [myScrollView release];    [activeField release];    [textFieldOne release];    [textFieldTwo release];    [textFieldThree release];    [textFieldFour release];    [super dealloc];}- (void)didReceiveMemoryWarning{    // Releases the view if it doesn't have a superview.    [super didReceiveMemoryWarning];        // Release any cached data, images, etc that aren't in use.}#pragma mark - View lifecycle// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.- (void)viewDidLoad{    [super viewDidLoad];        textFieldOne.delegate = self;    textFieldTwo.delegate = self;    textFieldThree.delegate = self;    textFieldFour.delegate = self;            myScrollView.contentSize = CGSizeMake(myScrollView.frame.size.width, 1400.0f);    myScrollView.scrollEnabled = YES;    myScrollView.delegate = self;        keyboardShown = NO;    [self performSelector:@selector(registerForKeyboardNotifications)];    }- (void)viewDidUnload{    [super viewDidUnload];    // Release any retained subviews of the main view.    // e.g. self.myOutlet = nil;}- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation{    // Return YES for supported orientations    return (interfaceOrientation == UIInterfaceOrientationPortrait);}#pragma mark - UITextField Delegate-(void)textFieldDidBeginEditing:(UITextField *)textField{    activeField = textField;}-(void)textFieldDidEndEditing:(UITextField *)textField{    activeField = nil;}-(BOOL)textFieldShouldReturn:(UITextField *)textField{    [textField resignFirstResponder];    return YES;}#pragma mark -Keyboard Helper Method// Call this method somewhere in your view controller setup code.- (void)registerForKeyboardNotifications{    [[NSNotificationCenter defaultCenter] addObserver:self                                             selector:@selector(keyboardWasShown:)                                                 name:UIKeyboardDidShowNotification object:nil];        [[NSNotificationCenter defaultCenter] addObserver:self                                             selector:@selector(keyboardWasHidden:)                                                 name:UIKeyboardDidHideNotification object:nil];}// Called when the UIKeyboardDidShowNotification is sent.- (void)keyboardWasShown:(NSNotification*)aNotification{    NSLog(@"-------");    if (keyboardShown)        return;        NSDictionary* info = [aNotification userInfo];        // Get the size of the keyboard.    NSValue* aValue = [info objectForKey:UIKeyboardBoundsUserInfoKey];    CGSize keyboardSize = [aValue CGRectValue].size;        // Resize the scroll view (which is the root view of the window)    CGRect viewFrame = [myScrollView frame];    viewFrame.size.height -= keyboardSize.height;    myScrollView.frame = viewFrame;            // Scroll the active text field into view.    CGRect textFieldRect = [activeField frame];    [myScrollView scrollRectToVisible:textFieldRect animated:YES];        oldContentOffsetValue = [myScrollView contentOffset].y;            CGFloat value = (activeField.frame.origin.y+myScrollView.frame.origin.y+activeField.frame.size.height - self.view.frame.size.height + keyboardSize.height)+2.0f;    if (value > 0) {        [myScrollView setContentOffset:CGPointMake(0, value) animated:YES];        isNeedSetOffset = YES;    }    keyboardShown = YES;}// Called when the UIKeyboardDidHideNotification is sent- (void)keyboardWasHidden:(NSNotification*)aNotification{    NSDictionary* info = [aNotification userInfo];        // Get the size of the keyboard.    NSValue* aValue = [info objectForKey:UIKeyboardBoundsUserInfoKey];    CGSize keyboardSize = [aValue CGRectValue].size;        // Reset the height of the scroll view to its original value    CGRect viewFrame = [myScrollView frame];    viewFrame.size.height += keyboardSize.height;    myScrollView.frame = viewFrame;            if (isNeedSetOffset) {        [myScrollView setContentOffset:CGPointMake(0, oldContentOffsetValue) animated:YES];    }    isNeedSetOffset = NO;    keyboardShown = NO;}@end

代碼有點長，一步步解析吧。

首先是viewDidLoad方法裡進行一些初始化處理：

- (void)viewDidLoad{    [super viewDidLoad];        textFieldOne.delegate = self;//設定textField的delegate，主要是為了顯示和隱藏彈出的鍵盤用的    textFieldTwo.delegate = self;    textFieldThree.delegate = self;    textFieldFour.delegate = self;        //使用scrollView很關鍵的地方，設定contentSize，一般是安你的scrollView的size來設定，後面的height可以適當多個300～400    myScrollView.contentSize = CGSizeMake(myScrollView.frame.size.width, 1400.0f);    myScrollView.scrollEnabled = YES;//這個預設就是YES，這裡多餘了。    myScrollView.delegate = self;//設定scrollView的delegate，需要監聽滾動事件的可以實現它的delegate方法        keyboardShown = NO;//一個狀態標誌，主要用來標識鍵盤的顯隱狀態    [self performSelector:@selector(registerForKeyboardNotifications)];//這個方法用來處理當textField被自己彈出的鍵盤擋住時，把它滾動到適當位置    }

接著就是相應的

registerForKeyboardNotifications方法，用來把textField滾動到適當的位置。

- (void)registerForKeyboardNotifications{    //添加自己做為觀察者，以擷取鍵盤顯示時的通知    [[NSNotificationCenter defaultCenter] addObserver:self                                             selector:@selector(keyboardWasShown:)                                                 name:UIKeyboardDidShowNotification object:nil];    //添加自己做為觀察者，以擷取鍵盤隱藏時的通知    [[NSNotificationCenter defaultCenter] addObserver:self                                             selector:@selector(keyboardWasHidden:)                                                 name:UIKeyboardDidHideNotification object:nil];}// 鍵盤出現時調用此方法- (void)keyboardWasShown:(NSNotification*)aNotification{    //如果鍵盤是顯示狀態，不用做重複的操作    if (keyboardShown)        return;        //獲得鍵盤通知的使用者資訊字典    NSDictionary* info = [aNotification userInfo];        // 取得鍵盤尺寸.    NSValue* aValue = [info objectForKey:UIKeyboardBoundsUserInfoKey];    CGSize keyboardSize = [aValue CGRectValue].size;        // 重新設定scrollView的size    CGRect viewFrame = [myScrollView frame];    viewFrame.size.height -= keyboardSize.height;    myScrollView.frame = viewFrame;            // 把當前被擋住的text field滾動到view中適當的可見位置.    CGRect textFieldRect = [activeField frame];    [myScrollView scrollRectToVisible:textFieldRect animated:YES];            //記錄當前textField的位移量，方便隱藏鍵盤時，恢複textField到原來位置    oldContentOffsetValue = [myScrollView contentOffset].y;        //計算textField滾動到的適當位置    CGFloat value = (activeField.frame.origin.y+myScrollView.frame.origin.y+activeField.frame.size.height - self.view.frame.size.height + keyboardSize.height)+2.0f;        //value>0則表示需要滾動，小於0表示當前textField沒有被擋住，不需要滾動    if (value > 0) {        //使textField滾動到適當位置        [myScrollView setContentOffset:CGPointMake(0, value) animated:YES];        isNeedSetOffset = YES;//更改狀態標誌為需要滾動    }    //更改鍵盤狀態標誌為已顯示    keyboardShown = YES;}// 鍵盤隱藏時調用此方法- (void)keyboardWasHidden:(NSNotification*)aNotification{        NSDictionary* info = [aNotification userInfo];        // Get the size of the keyboard.    NSValue* aValue = [info objectForKey:UIKeyboardBoundsUserInfoKey];    CGSize keyboardSize = [aValue CGRectValue].size;        // Reset the height of the scroll view to its original value    CGRect viewFrame = [myScrollView frame];    viewFrame.size.height += keyboardSize.height;    myScrollView.frame = viewFrame;        //如果狀態標誌為需要滾動，則要執行textFiled複位操作    if (isNeedSetOffset) {        //oldContentOffsetValue記錄了textField原來的位置，複位即可        [myScrollView setContentOffset:CGPointMake(0, oldContentOffsetValue) animated:YES];    }    //複位狀態標誌    isNeedSetOffset = NO;    keyboardShown = NO;}

這樣一個簡單的scrollView就做好了，滾動被擋住的內容到適當位置也是很常用的功能。