记录一下开发中掉进去的小坑坑

1、 页面跳转，不能再ViewDidLoad中进行，例如下面代码：

- (void)viewDidLoad {
    [super viewDidLoad];
 
    self.view.backgroundColor = [UIColor blueColor];
    
    SViewController *sc = [[SViewController alloc] init];
    [self presentViewController:sc animated:YES completion:nil];
    
}

这段代码让人失望，不会跳转的。把跳转写到别的生命周期函数，或者其他事件方法中即可。

2、 第三方键盘高度的问题

项目中用到了UITextView输入栏，但是当键盘弹出来时会挡住UITextView，因此需要对键盘弹出进行处理，具体做法就是监听系统发出的关于键盘的通知。可以用同一个通知监听弹出和收起，也可以分别监听。根据通知中字典的key值可以取到键盘的高度，然后对frame做相应的调整或者对约束进行修改。

问题来了。

对于第三方输入法，比如我用的搜狗输入法，iOS9.3.5，iPhone5，系统会发出3个通知，给出3个高度，因此你会看到屏幕上方一块黑色区域一闪而过，影响体验。获取到通知内容如下：

2016-09-02 15:20:20.752 [2898:1049771] {
    UIKeyboardAnimationCurveUserInfoKey = 7;
    UIKeyboardAnimationDurationUserInfoKey = "0.25";
    UIKeyboardBoundsUserInfoKey = "NSRect: {{0, 0}, {320, 0}}";
    UIKeyboardCenterBeginUserInfoKey = "NSPoint: {160, 568}";
    UIKeyboardCenterEndUserInfoKey = "NSPoint: {160, 568}";
    UIKeyboardFrameBeginUserInfoKey = "NSRect: {{0, 568}, {320, 0}}";
    UIKeyboardFrameEndUserInfoKey = "NSRect: {{0, 568}, {320, 0}}";
    UIKeyboardIsLocalUserInfoKey = 1;
}
2016-09-02 15:20:21.005 [2898:1049771] {
    UIKeyboardAnimationCurveUserInfoKey = 7;
    UIKeyboardAnimationDurationUserInfoKey = 0;
    UIKeyboardBoundsUserInfoKey = "NSRect: {{0, 0}, {320, 216}}";
    UIKeyboardCenterBeginUserInfoKey = "NSPoint: {160, 568}";
    UIKeyboardCenterEndUserInfoKey = "NSPoint: {160, 460}";
    UIKeyboardFrameBeginUserInfoKey = "NSRect: {{0, 568}, {320, 0}}";
    UIKeyboardFrameEndUserInfoKey = "NSRect: {{0, 352}, {320, 216}}";
    UIKeyboardIsLocalUserInfoKey = 1;
}
2016-09-02 15:20:21.125 [2898:1049771] {
    UIKeyboardAnimationCurveUserInfoKey = 7;
    UIKeyboardAnimationDurationUserInfoKey = 0;
    UIKeyboardBoundsUserInfoKey = "NSRect: {{0, 0}, {320, 256}}";
    UIKeyboardCenterBeginUserInfoKey = "NSPoint: {160, 460}";
    UIKeyboardCenterEndUserInfoKey = "NSPoint: {160, 440}";
    UIKeyboardFrameBeginUserInfoKey = "NSRect: {{0, 352}, {320, 216}}";
    UIKeyboardFrameEndUserInfoKey = "NSRect: {{0, 312}, {320, 256}}";
    UIKeyboardIsLocalUserInfoKey = 1;
}

3次获取到的高度是0，216，256。
解决办法，只使用第三次获取的值。具体操作有很多，我采用UIKeyboardFrameEndUserInfoKey获取到的高度减去UIKeyboardFrameBeginUserInfoKey获取到的高度，差值小于100，并且高度大于0，就视为第三次获取到的值。