1. Status bar: Set whether the network activity indicator is visible. If the network operation that the application is performing will last for more than a few seconds, the network activity indicator should be displayed. If the network operation will be completed in a few seconds, there is no need to display the network activity indicator, because it is likely to disappear before the user realizes its existence.

Specifies the color of the status bar. You can choose gray (the default color), opaque black or translucent black (that is, black with an alpha value of 0.5). Set whether the color change of the status bar should be dynamic.

2. Navigation bar: There is a circle of boxes with corners around the buttons on the navigation bar. In iPhone OS, this style is called border style. All controls in the navigation bar should use the border style. In fact, even if you put an unformatted (borderless) control on the navigation bar, it will automatically convert to a borderless style. ?

Although you can specify fonts for all the text displayed in the navigation bar, it is recommended that you use system fonts for readability. When you create a navigation bar using the appropriate UIKit programming interface, its title will be automatically displayed in the system font. ?

3. Tab bar: Tab bar should not be used as a toolbar. The difference is that the buttons on the toolbar work on elements in the current mode. The tab bar uses tabs to display icons and text. These tabs have the same width and the background is black. When you select a label, its background lights up and the image in the label highlights. ?

Note: No matter how the orientation of the device changes, the tab bar will not change its opacity and height. ?

4.Tab: it is the tab key of the keyboard, which is a way to indent the first line of each paragraph quickly, evenly and uniformly. It means to push the cursor to the next anchor point with a tabulator or a tabulator.

The Tab key on the keyboard is above the uppercase lock. Its most basic use is to draw a borderless table. Generally equal to the length of 8 spaces. When the spacing between words is achieved by pressing the Tab key, when there is a word in front, the sum of the word length and the word length can be divisible by 8.

Extended data:

Tab bar-Tab bar (navigation view)? Uitabaritem: UIToolbar-Toolbar (container view) In the iPhone, the toolbar is located on the screen, and the number of buttons cannot exceed 5. If there are more than 5 buttons, the fifth button (the last one) is more buttons. ?

In iPad, the toolbar is located on the screen, and the number of buttons is not controlled. In the toolbar, in addition to placing UIBarButtonItem, you can also place its custom view, which is only used in other special situations.

In UIBarButtonItem, in addition to the buttons you see, there are fixed spaces and variable spaces, which are used to insert certain spaces between buttons. ? UIBarButtonItem is a button in the toolbar and navigation bar.