OC, oc Language

OC, oc Language
 

Implementation

• To implement plotting, you usually need to define a subclass of UIView, override the parent class's-(void) drawRect :( CGRect) rect method, and implement plotting operations in this method

• To display the download progress, you only need to instantiate the object of the custom subclass (if it is a control in the storyboard, you only need to modify the class attribute of the control to the class Name of the custom subclass)
• The effect shown in the figure is to draw an arc, dynamically change the position of the endpoint, and finally reach a closed circle.

• The text in the middle is a UILabel control, which dynamically changes the text based on the progress.

Steps

• Customize a subclass of A UIView

  // Provide a member attribute to receive the download progress value @ property (nonatomic, assign) CGFloat progress;

• Override the setter of the member attribute progress

  // The setter-(void) setProgress (CGFloat) progress {_ progress = progress is called every time the value of the member property progress is changed; // when the download progress changes, manually call the redrawing method [self setNeedsDisplay];}

• Override-(void) drawRect :( CGRect) rect (Core)

  -(Void) drawRect :( CGRect) rect {// set the Arc radius CGFloat radius = rect. size. width * 0.5; // set the center of the arc CGPoint center = CGPointMake (radius, radius); // set the angle of the arc (in radians) CGFloat startAngle =-M_PI_2; // set the arc termination angle CGFloat endAngle =-M_PI_2 + 2 * M_PI * self. progress; // use the UIBezierPath class to draw an arc UIBezierPath * path = [UIBezierPath bezierPathWithArcCenter: center radius: radius-5 startAngle: startAngle endAngle: endAngle clockwise: YES]; // render the drawn arc to the layer (displayed) [path stroke];}