Problem description
TextField to enter the ID number, mobile phone number, bank card number every few Spaces need to be added. Delete from the end or middle of the textField if you make a typo, and then keep the contents of the current TextField in the format of a space every few bits. This article is mainly aimed at solving this problem
To solve the above problems, we should mainly solve two points:
- Cursor position
- Position of space
The above two cases can be divided into:
- Delete from last bit
- Remove from the middle
- Delete one and more at a time
- Add from the last bit
- Add from the middle
- Add one and a few bits at a time
In each case, cursor position and space position are taken into account, and each addition and deletion is recalculated.
Implementation:
Let’s start with a more detailed description of 👇’s proxy method:
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
Copy the coderange
ShouldChangeCharactersInRange: there are the location and length of two parameters, the location is about to be replaced the position of the length the length of the content is about to be replaced
string
The string used to replace the content in the range position
Suppose: TextField has content 1234
There are three ways to interpret string and range arguments:
- Deletes the last bit of the cursor: So the string is empty and the location of the range is the subscript of the content in front of the cursor is 3 and the length is 1 and the length of the deleted content is 1, and the result is that the string takes up the location of the range which is 123 and the 4 after 3 is taken up by the empty string which is deleted
- Cursor in the last bit delete two: operation, long press textField select 23, click delete. You can see that string is still empty, range is location=1, length=2 that is, position at subscript 1 is replaced by an empty string of length 2, 1 is left, and the so-called 23 is removed
- Add one: cursor in last bit. Enter a 2, range: location is 1, length is 0, the substituted content is at subscript 1 and length is empty. String is 2, so the result is a string with a subscript of 1 and a length of 0 is replaced by a string, that is, a 2 is added to the contents of the TextField, and the same applies to the contents of the range and string copied into the TextField
The point of this detail is to prepare for the next step.
Several properties and methods in the UITextInput protocol
Setting the cursor position requires the following two methods
// Get the cursor position offset from fromPosition. - (nullable UITextPosition *)positionFromPosition:(UITextPosition *)position offset:(NSInteger)offset; // create a UITextRange - (nullable UITextRange *)textRangeFromPosition:(UITextPosition *)fromPosition toPosition:(UITextPosition *)toPosition;Copy the codeMethod to set the cursor position
According to the UITextInput protocol two methods can be obtained to set the cursor position method
+ (void)setCursorLocation:(UITextField *)textField withOffset:(NSInteger) offset{// offset is the position where the cursor is to be located // generates a new postion UITextPosition *newPostion = [textField positionFromPosition:textField.beginningOfDocument offset:offset] ; / / set the cursor From one point to another point if the two points Then the point the cursor in the textField. SelectedTextRange = [textField textRangeFromPosition: newPostion toPosition:newPostion]; }Copy the codeNote: In textField, there is an attribute called selectedTextRange, which is of UITextRange type and contains two values [start,end]. Through experiments, it can be found that when no text is selected, the values of start and end represent the current cursor position. When a region is selected, start and end are the selected head and tail cursor positions, respectively
You can see that an important parameter in the setCursorLocation method is the offset
Method to add whitespace
InsertString :(NSString*)string withBlankLocations:(NSArray<NSNumber *>*)locations {if(! string) {return nil;
}
NSMutableString* mutableString = [NSMutableString stringWithString:[string stringByReplacingOccurrencesOfString:@"" withString:@""]].for (NSNumber *location in locations) {
if (mutableString.length > location.integerValue) {
[mutableString insertString:@""atIndex:location.integerValue]; }}return mutableString;
}
Copy the codeThe above method iterates through the string based on the position of the space passed in, adding a space to the string at the specified position. This method is called when the text in the textField changes, such as deleting or adding strings
So here’s how to calculate the offset set the cursor and add Spaces, depending on the situation
Delete string
How to determine is to click the keyboard delete
As mentioned above
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
Copy the codeDelete when string is empty in this proxy method. Range is a position that represents the position of the string. If the string is empty, range.length represents the length to delete
- Delete one bit if range.length == 1 if string is empty and range location is the length of the current textField.text subtracted by one location is the last character of textField.text
(1) If you delete the last bit, you do not need to set the cursor position and add a space
â‘¡ If it is not the last bit to delete a bit, it is necessary to determine whether the deletion is a space. If it is a space, it will be deleted twice
// Not the last bit NSInteger locationOffset = range.location;if (range.location < text.length && [text characterAtIndex:range.location] == ' '&& [textField.selectedTextRange isEmpty]) { [textField deleteBackward]; // Delete space locationOffset --; } [textField deleteBackward]; // Remove the character before the spaceCopy the codeThe above code calls [textField deleteBackward] twice and deletes twice
In this case, you need to change the position of the space and the position of the indicator. The offset is the value of range.location
- Range. Length > 1 indicates that the number of bits is deleted at one time
(1) Whether to start the deletion at the last digit. If the deletion is started at the last digit, the cursor position still does not need to be set, but the space position should be set
â‘¡ If it is not the last digit to start the deletion, the cursor position needs to be calculated, and the offset is still the current range.location
Add string
How do YOU determine add?
As mentioned above
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
Copy the codeThis proxy method adds when string is not empty. Range is a position that represents the position of the string if string is not empty. Range. length represents the length of the string to be added
If the entered string length does not exceed the limit, add it directly to the textField and then add Spaces in the desired location
TextField insertText:string [textField insertText:string]; / / the string in the textField change needs to be set Spaces textField. Text = [self insertString: textField. Text withBlankLocations: blankLocation];Copy the codeIn this case, the offset is calculated, and the cursor position is range.location + string.length, but if there is a space at the cursor position, the offset needs to be +1 as follows
NSInteger offset = range.location + string.length;
for (NSNumber *location in blankLocation) {
if (range.location == location.integerValue) {
offset ++;
}
}
[self setCursorLocation:textField withOffset:offset];
Copy the codeThrough the above several situations can solve the problem described at the beginning of the article.
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