flexDirection

Used to determine the item flow direction

flex=1
// This properties indicates the layout occupation percentage. 
// The occupation of layout is depends on {value}/{num of item in the same level}

// Given
<View style={{flex:1}}></View> // occupy 1/4
<View style={{flex:2}}></View> // occupy 2/4
<View style={{flex:1}}></View> // occupy 1/4

// This property means that 
// “please expand this component to fill the entire area content of the device”