render(){
    return(
    //这里调用.length是成功执行的
        {alert(this.props.rightTitle.length)}}>
            
                {this.props.title}
                {this.renderRightView()}
            
        
    )
}

renderRightView=()=>{
    if(this.props.isSwitch){
        return (
            {this.setState({isOn:!this.state.isOn})}} style={{marginRight:8}}/>
        )
    }
    else{
        return(
            
                {this.rightTitleView()}
                
            
        )
    }
}

rightTitleView(){
//这里调用.length是会报错的
    if(this.props.rightTitle.length)
    {
        return(
            {this.props.rightTitle}
        )
    }
}

具体错误是：undefined is not an object (evaluating this.props.rightTitle.length)