//通过runtime，我们发现UITextField有一个叫做_placeholderLabel的私有变量，下面来看下：

unsignedintcount =0;

Ivar*ivars =class_copyIvarList([UITextFieldclass], &count);

NSLog(@"count%d",count);

for(inti =0; i < count; i++) {

Ivarivar = ivars[i];

constchar*name =ivar_getName(ivar);

NSString*objcName = [NSStringstringWithUTF8String:name];

NSLog(@"%d : %@",i,objcName);

}

通过上面的代码已经证实确实有_placeholderLabel，这个私有变量，现在我们可以通过KVC来访问是有变量，并设置placeholder的颜色、字体等属性

UITextField*textField = [[UITextFieldalloc]initWithFrame:CGRectMake(0,100, [UIScreenmainScreen].bounds.size.width,30)];

[textFieldsetBackgroundColor:[UIColorgrayColor]];

[self.viewaddSubview:textField];

//_placeholderLabel

UILabel*placeHolderLabel = [[UILabelalloc]init];

placeHolderLabel.text=@"请输入文字";

placeHolderLabel.numberOfLines=0;

placeHolderLabel.textColor= [UIColorredColor];

[placeHolderLabelsizeToFit];

[textFieldaddSubview:placeHolderLabel];

//  字体保持一致

textField.font= [UIFontsystemFontOfSize:13.f];

placeHolderLabel.font= [UIFontsystemFontOfSize:13.f];

[textFieldsetValue:placeHolderLabelforKey:@"_placeholderLabel"];

}