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Control a JScrollpane  with keyboards

RobCSP
RobCSP asked
on
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Last Modified: 2008-02-01
Hi experts,

I have a JTextarea,inside a JscrollPane, the content exceeds the size of the area, for what I want that the user could see the whole content without need to use the mouse, that is to say, that could move the scroll by means of the keyboard.


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Mayank SPrincipal Technologist
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Commented:
Shall we assume that the JTextArea is ineditable? Because otherwise, you can use the Pg Down or the down-arrow buttons to go to the bottom of the text-area if the cursor is inside it.
Mayank SPrincipal Technologist
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Commented:
Top Expert 2004

Commented:
Hi RobCSP,

>> I have a JTextarea,inside a JscrollPane
Why do you need to put the JTextArea inside a JScrollPane ? JTextArea already have scrollbars.

Mayank SPrincipal Technologist
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Commented:
The java.awt.TextArea internally handles scrolling. JTextArea is different in that it doesn't manage scrolling, but implements the swing Scrollable interface. This allows it to be placed inside a JScrollPane if scrolling behavior is desired, and used directly if scrolling is not desired.
Mayank SPrincipal Technologist
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Commented:
You just need to set teh focus to the JScrollPane for doing that.

JScrollPane jsp = new JScrollPane ( t ) ; // t is an ineditable JTextArea
getContentPane ().add ( jsp ) ;
show () ;
jsp.requestFocus () ; // sets the focus to the JScrollPane

- then, you can try scrolling up and down with the Up/ Down arrow keys

Author

Commented:
Shall we assume that the JTextArea is ineditable? Yes

JTextArea already have scrollbars.
Are you sure???  

Keystroke-mappings are available for JScrollPane: I know that,but in this way you move the cursor, ok when you move the cursor,the scroll moves, but it produces strange jumps, that´s the reason why my boss(not me) want that the user control the scroll with the key arrows.

Can i add a keyListener to the JScrollPane and control the area displayed by it????

i come back in 2 hours thnx for the help


 

Mayank SPrincipal Technologist
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Commented:
You don't need to add any key-listener. Try out the requestFocus () example that I posted. Should work (works for me). JTextArea does not manage scrolling on its own, unlike TextArea. That's why it implements Scrollable, so that you can add it to a JScrollPane if scrolling is desired.

Author

Commented:
I try it, ok the  scroll works but this is not what i want because the jumps still happening, i want to control directly the scroll.

Test with a text that exceed the text area horizontal and vertically and you will see my problem.

thnx
Mayank SPrincipal Technologist
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Commented:
Try setting the unit-increment with jsp.getVerticalScrollBar ().setUnitIncrement () before you display the Container.
Mayank SPrincipal Technologist
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Commented:
Is my understanding of 'jump' correct? Do you mean that when you press the down-key, it scrolls a long way down the JTextArea? Is that correct?
Mayank SPrincipal Technologist
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Commented:
By the way, there is a significant difference in the amount it scrolls down if you use the Down button and the Page-Down button.
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Commented:
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Author

Commented:
Hi, i try with setUnitIncrement but the problem persist, my text area display text obtained from a text file

/************text example*********/

\n\n\n--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\nOPERACION              CONT                   TIPO                   ANUL                   MONEDA                                        CAMBIO                 CANTIDAD               EUROS                  NOMBRE                 DNI                    RESIDENCIA                                    FECHA                  USUARIO                \n--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\n\n67                                            VENTA DE BILLETES      SI                                                                                                                                        wqrwe                  wqeqw                  qweqe qweqeqw eqeq                            2004_04_06  13:30:13   Rob                    \n                                                                                            DOLAR USA                                     768                    0,8046408296           954.46                 \n\n\n\n\n--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\nOPERACION              CONT                   TIPO                   ANUL                   MONEDA                                        CAMBIO                 CANTIDAD               EUROS                  NOMBRE                 DNI                    RESIDENCIA                                    FECHA                  USUARIO                \n--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\n\n68                                            VENTA DE BILLETES      SI                                                                                                                                        wqrwe                  wqeqw                  qweqe qweqeqw eqeq                            2004_04_06  13:30:13   Rob                    \n                                                                                            DOLAR USA                                     768                    0,8046408296           954.46                 \n\n\n\n\n\n--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\nOPERACION              CONT                   TIPO                   ANUL                   MONEDA                                        CAMBIO                 CANTIDAD               EUROS                  NOMBRE                 DNI                    RESIDENCIA                                    FECHA                  USUARIO                \n--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\n\n69                                            VENTA DE BILLETES      SI                                                                                                                                        wqrwe                  wqeqw                  qweqe qweqeqw eqeq                            2004_04_06  13:30:13   Rob                    \n                                                                                            DOLAR USA                                     768                    0,8046408296           954.46                 \n\n\n\n\n\n--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\nOPERACION              CONT                   TIPO                   ANUL                   MONEDA                                        CAMBIO                 CANTIDAD               EUROS                  NOMBRE                 DNI                    RESIDENCIA                                    FECHA                  USUARIO                \n--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\n\n70                                            VENTA DE BILLETES      SI                                                                                                                                        wqrwe                  wqeqw                  qweqe qweqeqw eqeq                            2004_04_06  13:30:13   Rob                    \n                                                                                            DOLAR USA                                     768                    0,8046408296           954.46                 \n





/************ end of text example************/


Because of the blank lines, if i move the cursor the "jumps" begin, that the reason why i want to know if i can control directly the displayed area of a JscrollPane.

i see the links, but i don´t find it useful.

Mayank SPrincipal Technologist
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Commented:
Well, the setUnitIncrement () method is perhaps meant for that purpose only. There is also one setBlockIncrement () but I don't know what it does - never tried it. Try printing the value of unit-increment by getUnitIncrement (). Does it give something close to 10? Try setting it to 1.
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