當我們想找到一個視圖的子視圖相對于當前控制器中的坐標位置時，用坐標轉換就可以很方便的找到了，如下圖所示：

如圖所示：從下到上依次是 self.view --> redView -->yellowView

redView的坐標：{{20, 20}, {335, 627}}，加在控制器的view上

yellowView的坐標：{{20, 20}, {295, 587}}，加在redView上

CGSize size = self.view.frame.size;

UIView *redView = [[UIView alloc] initWithFrame:CGRectMake(20, 20, size.width - 40, size.height - 40)];

redView.backgroundColor = [UIColor redColor];

[self.view addSubview:redView];

UIImageView *yellowView = [[UIImageView alloc] initWithFrame:CGRectMake(20, 20, redView.frame.size.width - 40, redView.frame.size.height - 40)];

yellowView.backgroundColor = [UIColor yellowColor];

[redView addSubview:yellowView];

NSLog(@"%@ --- %@", NSStringFromCGRect(redView.frame), NSStringFromCGRect(yellowView.frame));

//? ? 輸出{{20, 20}, {335, 627}} --- {{20, 20}, {295, 587}}

//把 yellowView.frame 從 redView 的坐標系轉換到 self.view 的坐標系

// 如果傳入的是 yellowView.frame，則要用 yellowView 的父視圖來調用，toView：傳入的參數是最終要轉換到的那個視圖。

//? ? CGRect rect = [redView convertRect:yellowView.frame toView:self.view];? ? // 這個和下面一句一樣

// 如果傳入的是 yellowView.bounds，則要用 yellowView 本身來調用，toView：傳入的參數是最終要轉換到的那個視圖。

CGRect rect = [yellowView convertRect:yellowView.bounds toView:self.view]; // 這個和上面一句一樣

CGRect frame = [self.view convertRect:yellowView.frame fromView:redView];

NSLog(@"%@, %@", NSStringFromCGRect(rect), NSStringFromCGRect(frame));

//? ? 輸出{{40, 40}, {295, 587}}, {{40, 40}, {295, 587}}

//把 yellowView.frame.origin 從 redView 的坐標系轉換到 self.view 的坐標系

CGPoint point = [redView convertPoint:yellowView.frame.origin toView:self.view];

CGPoint point1 = [self.view convertPoint:yellowView.frame.origin fromView:redView];

NSLog(@"%@, %@", NSStringFromCGPoint(point), NSStringFromCGPoint(point1));

// 輸出{40, 40}, {40, 40}