IOS development -- what if ARGB/RGBA is used, ios -- argbrgba

IOS development -- what if ARGB/RGBA is used, ios -- argbrgba

I. Preface

During iOS development, we often use hexadecimal notation to represent the color value. In general, we use this notation: for example, #000000 represents the black color and # ffffff represents the white color, but what if we want transparency?

Next let's take a look at how to obtain the color values of argb/rgba.

2. First, let's take a look at the basic knowledge (it has nothing to do with iOS and is common)

1. hexadecimal color code

In short, a 6-digit hexadecimal value starting with # represents a color.

In rgb, red can be expressed as (255, 0, 0). Then 255/16 is converted to hexadecimal (is used for calculation here), that is, FF, 0, or 00, therefore, the red hexadecimal representation is # FF0000.

2. Shift left </shift right>

12 <2. What is the result of moving 12 to the left two places?

First, convert 12 to 2: 1100, and then move 1100 to the left, and then add 0 to the number of digits, that is, 0000, that is, 0.

12> 2, convert it to 1100, and then shift it to the right of 2 places. Fill in 0 for the remaining digits, that is, 0011, that is, 3.

3. Go to iOS and process argb

Put the following code directly:

+ (UIColor *) colorWithHextColorString :( NSString *) hexColorString {// here is alpha pass 1. In colorWithHextColorString alpha, alpha is modified to return [self colorWithHextColorString: hexColorString alpha: 1.0f];} // supports rgb, argb + (UIColor *) colorWithHextColorString :( NSString *) hexColorString alpha :( CGFloat) alphaValue {UIColor * result = nil; unsigned int colorCode = 0; unsigned char redByte, greenByte, blueByte; // exclude @ \ "I F ([hexColorString hasPrefix: @ "@ \" "]) {hexColorString = [hexColorString substringWithRange: NSMakeRange (2, hexColorString. length-3)];} // exclude # if ([hexColorString hasPrefix: @ "#"]) {hexColorString = [hexColorString substringFromIndex: 1];} if (nil! = HexColorString) {NSScanner * callback = [NSScanner scannerWithString: hexColorString]; (void) [Export scanHexInt: & colorCode]; // ignore error} redByte = (unsigned char) (colorCode> 16); greenByte = (unsigned char) (colorCode> 8); blueByte = (unsigned char) (colorCode ); // masks off high bits if ([hexColorString length] = 8) {// if it is 8 bits, then alpha alphaValue = (float) (unsigned char) (colorCode> 24)/0xff;} NSLog (@ "alpha: % f ---- r: % f ---- g: % f ---- B: % f", alphaValue, (float) redByte/0xff, (float) greenByte/0xff, (float) blueByte/0xff); result = [UIColor colorWithRed: (float) redByte/0xff green: (float) greenByte/0xff blue: (float) blueByte/0xff alpha: alphaValue]; return result ;}

For example, FF0000. The result is as follows:

AEFF0000 (AE: 10 stands for 174). The running result is as follows:

The argb parsing method is perfectly implemented.

Briefly introduces its implementation:

First, set the alpha value of the colorWithHextColorString: alpha: Method to 1, that is, opacity.

Then, in colorWithHextColorString: alpha:, first filter out other illegal characters of the passed hexColorString, such. Then, use NSScanner to scan the data and convert it into a 10-digit system.

Then, the values of red, green, and blue are obtained through the shift operation. If the value of hexColorString is 8 bits, it means that hexColorString contains the alpha value, and the value of alphaValue is obtained by 24 bits to the right.

Finally

+ (UIColor *)colorWithRed:(CGFloat)red green:(CGFloat)green blue:(CGFloat)blue alpha:(CGFloat)alpha;

Method to set its color.

What is hard to understand here is the shift operation. Let's give a brief introduction.

First, the hexColorString after @ \ "and # are excluded as AEFF0000, and then the colorCode of the scan result is: 2935947264. Then perform the shift operation (using the above method), set the result of colorCode> 16 to 44799 (in the console po colorCode> 16), and use the calculator to calculate the value. The output is as follows:

po (unsigned char)(colorCode>>16)

The result is \ xff, that is, the hexadecimal ff, that is, the red part of the hexColorString. Here, we only add an unsigned char, and it turns into a hexadecimal ff, which is a bit hard to understand (maybe Apple converted it internally) and then reused.

(float)(unsigned char)(colorCode>>16)/0xff

Get the float value and substitute it into the class method of UIColor for parsing. Finally, obtain the required color.

Note: For rgba, you can modify the shift slightly to implement rgba resolution.

Iv. Conclusion

That's simple. Contact us if you have any questions.