通过运行时，发现UITextView有一个叫做“_placeHolderLabel”的私有变量，
Ivar *ivars = class_copyIvarList([UITextView class], &count);
for (int i = 0; i < count; i++) {
Ivar ivar = ivars[i];
const char *name = ivar_getName(ivar);
NSString *objcName = [NSString stringWithUTF8String:name];
NSLog(@"%d : %@",i,objcName);
}
so
- (UITextView *)reasonTextView {
if (!_reasonTextView) {
_reasonTextView = [[UITextView alloc] initWithFrame:CGRectMake(10, self.addReason.bottom + 20, kScreenW - 20, 150)];
[_reasonTextView setBackgroundColor:RGBOF(0xF3F3F4)];
UILabel *placeHolderLabel = [[UILabel alloc] init];
placeHolderLabel.text = @"输入你想加入此家族的原因，最少5个字";
placeHolderLabel.numberOfLines = 0;
placeHolderLabel.textColor = [UIColor lightGrayColor];
[placeHolderLabel sizeToFit];
[_reasonTextView addSubview:placeHolderLabel];
// same font
_reasonTextView.font = [UIFont systemFontOfSize:16.f];
placeHolderLabel.font = [UIFont systemFontOfSize:16.f];
[_reasonTextView setValue:placeHolderLabel forKey:@"_placeholderLabel"];
_reasonTextView.delegate = self;
}
return _reasonTextView;
}
