iphone:保持表單輸入的可見性——自動滾動視圖

iPhone: Maintain visibility of form inputs – auto-scrolling views

當你開發圖標或者任何有輸入區域的界面，偶爾輸入框再鍵盤彈出時會被擋住。這樣用戶體驗不好，用戶在輸入時看不到他們所輸入的東西。一個解決方案，是滑動整個view讓編輯區域一直是可見的。

我提供的整個解決方案對UIView添加了一些方法（我知道，添加類別到cocoa的類是頑皮的）這將決定基于整個屏幕的輸入位置滑動視圖的多少，還有和鍵盤彈起一樣的速度滑動視圖。在編輯完成時滑動回到原來的位置。

做到這樣很簡單，這是我如何通過計算來滾動視圖：

- (void) maintainVisibityOfControl:(UIControl *)control offset:(float)offset {
	static const float deviceHeight = 480;
	static const float keyboardHeight = 216;
	static const float gap = 5; //gap between the top of keyboard and the control

	//Find the controls absolute position in the 320*480 window - it could be nested in other views
	CGPoint absolute = [control.superview convertPoint:control.frame.origin toView:nil];

	//If it would be hidden behind the keyboard....
	if (absolute.y > (keyboardHeight + gap)) {
		//Shift the view
		float shiftBy = (deviceHeight - absolute.y) - (deviceHeight - keyboardHeight - gap - offset);
		[UIView beginAnimations:nil context:nil];
		[UIView setAnimationDuration:0.3f]; //this is speed of keyboard
		CGAffineTransform slideTransform = CGAffineTransformMakeTranslation(0.0, shiftBy);
		self.transform = slideTransform;
		[UIView commitAnimations];
	}
}

..然后我重置了視圖通過使用：

- (void) resetViewToIdentityTransform {
	[UIView beginAnimations:nil context:nil];
	[UIView setAnimationDuration:0.3f]; //this is speed of keyboard
	CGAffineTransform slideTransform = CGAffineTransformIdentity;
	self.transform = slideTransform;
	[UIView commitAnimations];
}

你只需要對你的代碼做一些小的改動，并在UITextFieldDelegate調用這些方法（或其他控制代理）：

- (void) textFieldDidBeginEditing:(UITextField *)textField {
	[self.view maintainVisibityOfControl:textField offset:0.0f];
}

- (void)textFieldDidEndEditing:(UITextField *)textField {
	if (textField == currentControl) {
		//If the textfield is still the same one, we can reset the view animated
		[self.view resetViewToIdentityTransform];
	}else {
		//However, if the currentControl has changed - that indicates the user has
		//gone into another control - so don't reset view, otherwise animations jump around
	}
}

這里是工程拷貝(見附件)。