1、全局异步执行耗时任务

dispatch_async(dispatch_get_global_queue(0, 0), ^{

});

2.主线程异步刷新UI

dispatch_async(dispatch_get_main_queue(), ^{

});

3.改变PlaceHolder的颜色

[username_text setValue:[UIColor colorWithRed:1 green:1

blue:1 alpha:0.5]

forKeyPath:@"_placeholderLabel.textColor"];

4.解决键盘弹起挡住文本框的问题

//键盘弹起时重置View大小

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent

*)event{

[username_text resignFirstResponder];

[password_text resignFirstResponder];

NSTimeInterval animationDuration = 0.30f;

[UIView beginAnimations:@"ResizeForKeyboard"context:nil];

[UIView setAnimationDuration:animationDuration];

CGRect rect = CGRectMake(0.0f, 0.0f,self.view.frame.size.width,self.view.frame.size.height);

self.view.frame = rect;

[UIView commitAnimations];

}

//退出编辑（键盘落下）重置View大小

- (BOOL)textFieldShouldReturn:(UITextField *)textField

{

NSTimeInterval animationDuration = 0.30f;

[UIView beginAnimations:@"ResizeForKeyboard"context:nil];

[UIView setAnimationDuration:animationDuration];

CGRect rect = CGRectMake(0.0f, 0.0f,self.view.frame.size.width,self.view.frame.size.height);

self.view.frame = rect;

[UIView commitAnimations];

[textField resignFirstResponder];

return YES;

}

5.开始编辑（键盘弹起）通过控件Y坐标计算View显示范围

- (void)textFieldDidBeginEditing:(UITextField *)textField

{

CGRect frame = password_text.frame;

int offset = frame.origin.y + 32 -

(self.view.frame.size.height - 216.0);

NSTimeInterval animationDuration = 0.30f;

[UIView beginAnimations:@"ResizeForKeyBoard"

context:nil];

[UIView setAnimationDuration:animationDuration];

floatwidth =self.view.frame.size.width;

floatheight =self.view.frame.size.height;

if(offset > 0)

{

CGRect rect = CGRectMake(0.0f, -

offset,width,height);

self.view.frame = rect;

}

[UIView commitAnimations];

}