1-1Did End On Exit 调用下面事件当点击键盘return得时候就会隐藏键盘
- (IBAction)textFieldShouldReturn:(UITextField *)textField {
    //[sender resignFirstResponder];
    if (textField == chi) {
        [chi resignFirstResponder];
        doublem=[chi.textdoubleValue]/3.003;
        double f=m *3.2808;
        meter.text=[[NSStringalloc]initWithFormat:@"%.4f",m];
        feet.text=[[NSStringalloc]initWithFormat:@"%.4f",f];
    }
    if (textField == meter) {
        [meter resignFirstResponder];
        
    }
    if (textField == feet) {
        [feet resignFirstResponder];
    }
}
1-2 点击屏幕得时候隐藏键盘
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent*)event{
    UITouch *touch=[[event allTouches] anyObject];
    if (touch.tapCount >=1) {
        [chi resignFirstResponder];
        [meter resignFirstResponder];
        [feet resignFirstResponder];
    }
}

1-2的方法相当于屏幕任何位置的点击事件（除了各组件的点击处）可以在这个方法里执行要隐藏或remove的view。

隐藏键盘的两种方法