The use of android Rect class

Today, let's talk about the use of Android's Rect class.

public final class

Rect

extends Object
implements Parcelable

java.lang.Object
↳	android.graphics.Rect

Public Constructors
	Rect() Create a new empty Rect.
	Rect(int left, int top, int right, int bottom) Create a new rectangle with the specified coordinates.
	Rect(Rect r) Create a new rectangle, initialized with the values in the specified rectangle (which is left unmodified).

Public Methods
final int	centerX () gets the matrix center point (x, y)
final int	centerY()
boolean	contains (int x, int y) whether to contain the (x, y) point Returns true if (x,y) is inside the rectangle.
boolean	contains (int left, int top, int right, int bottom) whether to contain ( int left, int top, int right, int bottom ) matrix Returns true iff the 4 specified sides of a rectangle are inside or equal to this rectangle.
boolean	contains(Rect r) Returns true iff the specified rectangle r is inside or equal to this rectangle.
int	describeContents() Parcelable interface methods
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
final float	exactCenterX () This method is similar to CenterX(), but this method is more accurate (returns float type)
final float	exactCenterY()
String	flattenToString() Return a string representation of the rectangle in a well-defined format.
final int	height()
void	inset(int dx, int dy) Inset the rectangle by (dx,dy).
boolean	intersect(Rect r) If the specified rectangle intersects this rectangle, return true and set this rectangle to that intersection, otherwise return false and do not change this rectangle.
boolean	intersect(int left, int top, int right, int bottom) If the rectangle specified by left,top,right,bottom intersects this rectangle, return true and set this rectangle to that intersection, otherwise return false and do not change this rectangle.
boolean	intersects(int left, int top, int right, int bottom) Returns true if this rectangle intersects the specified rectangle.
static boolean	intersects(Rect a, Rect b) Returns true iff the two specified rectangles intersect.
final boolean	isEmpty() Returns true if the rectangle is empty (left >= right or top >= bottom)
void	offset (int dx, int dy) The offset of the matrix in the x-axis and y-axis respectively (very useful, you can move the matrix up and down) Offset the rectangle by adding dx to its left and right coordinates, and adding dy to its top and bottom coordinates.
void	offsetTo (int newLeft, int newTop) maintains the width and height of the matrix, and the upper left corner of the matrix is ​​offset to (newLeft, newTop) this point Offset the rectangle to a specific (left, top) position, keeping its width and height the same.
void	readFromParcel(Parcel in) Set the rectangle's coordinates from the data stored in the specified parcel.
void	set(int left, int top, int right, int bottom) Set the rectangle's coordinates to the specified values.
void	set(Rect src) Copy the coordinates from src into this rectangle.
void	setEmpty () Set the rectangle to (0,0,0,0)
boolean	setIntersect(Rect a, Rect b) If rectangles a and b intersect, return true and set this rectangle to that intersection, otherwise return false and do not change this rectangle.
void	sort() Swap top/bottom or left/right if there are flipped (i.e.
String	toShortString() Return a string representation of the rectangle in a compact form.
String	toString() Returns a string containing a concise, human-readable description of this object.
static Rect	unflattenFromString(String str) Returns a Rect from a string of the form returned by  flattenToString() , or null if the string is not of that form.
void	union(int left, int top, int right, int bottom) Update this Rect to enclose itself and the specified rectangle.
void	union(Rect r) Update this Rect to enclose itself and the specified rectangle.
void	union(int x, int y) Update this Rect to enclose itself and the [x,y] coordinate.
final int	width()
void	writeToParcel(Parcel out, int flags) Write this rectangle to the specified parcel.

1.   new Rect(150, 75, 260, 120)  

  This constructor requires four parameters. What do these four parameters indicate ? Let's explain how to draw this rectangle . The four parameters represent: left top right bottom   , up, down, left and right. Ah, not top left and bottom right . Let me explain left  : the X coordinate of the left side of the rectangle   150   top:     the Y coordinate of the top of the rectangle    75      right:   the X coordinate of the right side of the rectangle    260     bottom : the Y coordinate of the bottom of the rectangle  120         
          
 


 

To put it bluntly, the coordinates of the upper left corner are (150,75), and the coordinates of the lower right corner are (260,120), so it is easy to understand

2. What is the difference between the Rect class and the RectF class (android.graphics.RectF)??

Answer: The main difference is in the precision, they are: int, float type

这里需要注意一点，Rect类主要用于表示坐标系中的一块矩形区域，并可以对其做一些简单操作。这块矩形区域，需要用左上右下两个坐标点表示（left,top,right,bottom）,你也可以获取一个Rect实例的Width和Height。就在这里，奇葩的事情来了，作为一个有一点经验的做图像或者矩阵运算或者编程的程序员来说，大家的共识是，如果一个矩阵是MxN的，也就是M行N列，那么行号是[0,M-1],列号是[0,N-1]。可是奇葩的Rect类并不是这样的！如果你这么声明一个Rect类：

Rect rect= new Rect( 100 , 50 , 300 , 500 );

那么右下角(300,500)其实是不在这个矩形里面的，但是左上角(100,50)在，也就是说，这个矩形实际表示的区域是：(100,50,299,499)。另外，Rect计算出的Height和Width倒是对的。所以，在此告诫各位程序员，在涉及Rect运算的时候，尽量不要使用它的右下角左边，即right和bottom。因为他们是错的。当然，在你调用android自己的函数时，是可以使用的，因为Android里面一直保持这么奇葩的思维。

android Rect类的使用就讲完了。

就这么简单。