Placeholder

我们有时需要定制化UITextField对象的风格，可以添加许多不同的重写方法，来改变文本字段的显示行为。这些方法都会返回一个CGRect结构，制定了文本字段每个部件的边界范围，甚至修改placeHolder颜色，字体,有些方法对UITextView同样适用。

- (CGRect)textRectForBounds:(CGRect)bounds      //重写来重置文字区域
- (void)drawTextInRect:(CGRect)rect//改变绘文字属性.重写时调用super可以按默认图形属性绘制,若自己完全重写绘制函数，就不用调用super了.
- (CGRect)placeholderRectForBounds:(CGRect)bounds  　//重写来重置占位符区域
- (void)drawPlaceholderInRect:(CGRect)rect  　　              //重写改变绘制占位符属性.重写时调用super可以按默认图形属性绘制,若自己完全重写绘制函数，就不用调用super了
- (CGRect)borderRectForBounds:(CGRect)bounds　　        //重写来重置边缘区域
- (CGRect)editingRectForBounds:(CGRect)bounds　　        //重写来重置编辑区域
- (CGRect)clearButtonRectForBounds:(CGRect)bounds　  　//重写来重置clearButton位置,改变size可能导致button的图片失真
- (CGRect)leftViewRectForBounds:(CGRect)bounds
- (CGRect)rightViewRectForBounds:(CGRect)bounds

通过- (void)drawPlaceholderInRect:(CGRect)rect 方法可改变placeHolder颜色、字体，请看代码：
自定义一个类CustomTextField让它继承UITextField实现以下方法即可：

    //控制清除按钮的位置
-(CGRect)clearButtonRectForBounds:(CGRect)bounds
{
   return CGRectMake(bounds.origin.x + bounds.size.width - 50, bounds.origin.y + bounds.size.height -20, 16, 16);
}

//控制placeHolder的位置，左右缩20
-(CGRect)placeholderRectForBounds:(CGRect)bounds
{
    
    //return CGRectInset(bounds, 20, 0);
   CGRect inset = CGRectMake(bounds.origin.x+20, bounds.origin.y, bounds.size.width, bounds.size.height);//更好理解些
   return inset;
}
//控制显示文本的位置
-(CGRect)textRectForBounds:(CGRect)bounds
{
    //return CGRectInset(bounds, 50, 0);
    CGRect inset = CGRectMake(bounds.origin.x+190, bounds.origin.y, bounds.size.width -10, bounds.size.height);//更好理解些
    return inset;

}

//控制编辑文本的位置
-(CGRect)editingRectForBounds:(CGRect)bounds
{
    //return CGRectInset( bounds, 10 , 0 );
    
   CGRect inset = CGRectMake(bounds.origin.x +10, bounds.origin.y, bounds.size.width -10, bounds.size.height);
   return inset;
}

//控制左视图位置
- (CGRect)leftViewRectForBounds:(CGRect)bounds
{
   CGRect inset = CGRectMake(bounds.origin.x +10, bounds.origin.y, bounds.size.width-250, bounds.size.height);
   return inset;
    //return CGRectInset(bounds,50,0);
}

//控制placeHolder的颜色、字体
- (void)drawPlaceholderInRect:(CGRect)rect
{
    //CGContextRef context = UIGraphicsGetCurrentContext();
    //CGContextSetFillColorWithColor(context, [UIColor yellowColor].CGColor);
    [[UIColororangeColor] setFill];
    
    [[selfplaceholder] drawInRect:rectwithFont:[UIFontsystemFontOfSize:20]];
}

下面是使用CustomTextField的代码，可放在viewDidLoad等方法中

     _textField = [[CustomTextField alloc] initWithFrame:CGRectMake(20, 150, 280, 30)];
    _textField.placeholder = @"手机号";
    _textField.borderStyle = UITextBorderStyleRoundedRect;
    _textField.textAlignment = UITextAlignmentLeft;
    _textField.delegate = self;
    _textField.clearButtonMode = UITextFieldViewModeWhileEditing;
    //_textField.text = @"随便";
    UIImageView *imgv = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"anyImage.png"]];
    _textField.leftView = imgv;
    _textField.leftViewMode = UITextFieldViewModeAlways;
    [self.view addSubview:_textField];

还可以将placeholder的字体设置为倾斜，正常的情况下直接设置使用italicSystemFontOfSize：是只能显示英文的斜体，中文是不可以的，使用如下方法可以使中文倾斜

    - (void)drawPlaceholderInRect:(CGRect)rect
{
    CGAffineTransform matrix =  CGAffineTransformMake(1, 0, tanf(15 * (CGFloat)M_PI / 180), 1, 0, 0);
    CGFloat size=self.font.pointSize;
    UIFontDescriptor *desc = [ UIFontDescriptor fontDescriptorWithName :self.font.fontName matrix :matrix];
    UIFont *font = [ UIFont fontWithDescriptor :desc size :size];
    [[UIColor lightGrayColor] set]; //颜色会自动变成黑色,所以需要手动设置为灰色
    [self.placeholder drawInRect:rect withFont:font lineBreakMode:NSLineBreakByTruncatingTail];
    
}