Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); //设置线程优先级为后台

int THREAD_PRIORITY_AUDIO //标准音乐播放使用的线程优先级

int THREAD_PRIORITY_BACKGROUND //标准后台程序

int THREAD_PRIORITY_DEFAULT // 默认应用的优先级

int THREAD_PRIORITY_DISPLAY //标准显示系统优先级，主要是改善UI的刷新

int THREAD_PRIORITY_FOREGROUND //标准前台线程优先级

int THREAD_PRIORITY_LESS_FAVORABLE //低于favorable

int THREAD_PRIORITY_LOWEST //有效的线程最低的优先级

int THREAD_PRIORITY_MORE_FAVORABLE //高于favorable

int THREAD_PRIORITY_URGENT_AUDIO //标准较重要音频播放优先级

int THREAD_PRIORITY_URGENT_DISPLAY //标准较重要显示优先级，对于输入事件同样适用。

- (void)addKeyboardObserver
{
    // This could be in an init method.
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardDidShow:) name:UIKeyboardDidShowNotification object:nil];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardDidHide:) name:UIKeyboardDidHideNotification object:nil];
}

- (void)keyboardDidShow:(NSNotification*)notification
{
    NSDictionary* keyboardInfo = [notification userInfo];
    NSValue* keyboardFrameBegin = [keyboardInfo valueForKey:UIKeyboardFrameBeginUserInfoKey];
    _keyboardFrameBeginRect = [keyboardFrameBegin CGRectValue];
    UIScrollView *_scrollView = (UIScrollView*)self.view;
    _scrollView.frame = CGRectMake(_scrollView.frame.origin.x,
                                   _scrollView.frame.origin.y,
                                   _scrollView.frame.size.width,
                                   _scrollView.frame.size.height - _keyboardFrameBeginRect.size.height);
}

- (void)keyboardDidHide:(NSNotification*)notification
{
    UIScrollView *_scrollView = (UIScrollView*)self.view;
    _scrollView.frame = CGRectMake(_scrollView.frame.origin.x,
                                   _scrollView.frame.origin.y,
                                   _scrollView.frame.size.width,
                                   _scrollView.frame.size.height +
                               _keyboardFrameBeginRect.size.height);
}

 (void)textViewDidChange:(UITextView *)textView
{
    UIScrollView *_scrollView = (UIScrollView*)self.view;
    _textView.frame = CGRectMake(_textView.frame.origin.x,
                                 _textView.frame.origin.y,
                                 _textView.contentSize.width,
                                 _textView.contentSize.height);
    _scrollView.contentSize = _textView.frame.size;

    if (_scrollView.frame.size.height < _textView.frame.size.height) {
        CGPoint bottomOffset = CGPointMake(0,_textView.frame.size.height-_keyboardFrameBeginRect.size.height);
        [_scrollView setContentOffset:bottomOffset animated:NO];
    }
}