Develop Reference

(Kind of solved but still appreciate better answers) Android Studio: How to identify certain special pages in a PDF file?

I am writing an app that generates Maths worksheets for school students. It will, for example, generate 2 to 5 pages of simple Maths questions and 1 to 2 pages of answers. The PDF can be saved to file and loaded again later. Then it has a print function that can print all the pages. I want to make it skip printing the answer pages.
Is it possible to automatically identify which pages are the answer pages? I can only think of a workaround by making those answer pages have special height or width but not even sure if this works. Are there any better ways to do this?

Ok, I continued the project and used the following method: when constructing the PDF, I put the word "Answer on the top left corner with a gray rectangle surrounding it drawn with drawRect(). Then before the actual printing, I used the following code inside the PrintDocumentAdapter() class to check whether the color of the pixel 0,0 is gray or not.
#Override
public void onStart() {
if (parcelFileDescriptor != null) {
try {
pdfRenderer = new PdfRenderer(parcelFileDescriptor);
} catch (IOException e) {
e.printStackTrace();
}
}
int tempTotal = pdfRenderer.getPageCount();
Bitmap[] tempBitmap = new Bitmap[tempTotal];
finalTotal = tempTotal;
for (int pageNum = 0; pageNum < tempTotal; pageNum++) {
PdfRenderer.Page tempPage = pdfRenderer.openPage(pageNum);
tempBitmap[pageNum] = Bitmap.createBitmap(WS_WIDTH, WS_HEIGHT, Bitmap.Config.ARGB_8888);
tempPage.render(tempBitmap[pageNum], null, null, PdfRenderer.Page.RENDER_MODE_FOR_PRINT);
if (tempBitmap[pageNum].getPixel(0, 0) == Color.GRAY) {
finalTotal--;
}
tempPage.close();
}
}
It works fine. At least should cause no problem if the users only attempt to print PDF files constructed with my app. :P
Please tell me if you know a better way to do this. Thanks!

GWT infinite scroll with discarding start-of-list results

Looking for a GWT DataGrid component which implements infinite scroll, BUT also makes sure to discard the results no longer visible on the screen : such as the previously loaded results that are not shown anymore.
This is to avoid a memory hog.
I've been trying to find this on Google, but no luck so far.
Please note : I could take a JS library and adapt it to what I need, but I don't think it would work good with GWT's DataGrid component.
Edit: I am interested specifically in an infinite scroll which ALSO discards/releases the topmost results that are not visible (and loads them up as appropriate).
Any ideas ?

As a matter of fact the showcase example has an infinite scrolling CellList. (you can find the code there).
Although this was done with a CellList the same principles should also apply to a DataGrid.
Check out the ShowMorePagerPanel.java file.
Update:
The onScroll function of ShowMorePagerPanel.java will add the new records at the bottom. However you can easily change the behavior:
Something along the lines (not tested tough):
HasRows display = getDisplay();
if (display == null) {
return;
}
boolean loadData = false;
// If scrolling up, change newStart
int oldScrollPos = lastScrollPos;
lastScrollPos = scrollable.getVerticalScrollPosition();
// get the current visible Range
Range currentRange = display.getVisibleRange();
if (oldScrollPos >= lastScrollPos) {
int newStart = Math.max(
currentRange.getStart() - incrementSize,0);
loadData = true;
}
int maxScrollTop = scrollable.getWidget().getOffsetHeight()
- scrollable.getOffsetHeight();
if (lastScrollPos >= maxScrollTop) {
// We are near the end, so increase the page size.
int newPageSize = Math.min(
display.getVisibleRange().getLength() + incrementSize,
display.getRowCount());
loadData = true;
}
if (loadData) {
display.setVisibleRange(newStart, newPageSize);
}

java - (slick2D) Move Sprite Set Distance at Set Speed on Keypress

So I've been trying to write a simple game where a character is moving using the statement
character1.x+=0.1f*delta
where delta is the time (in milliseconds) between frames. This works well when I want to move it every frame, but I want to be able to move it a set distance (50 pixels, or a single tile in my game) at that speed. Using for() loops makes it move the sprite at maximum speed, so I can't do that. It has to work on a single keypress, so they don't have to hold the key down.
Of course, I've barely done anything ever in Java, so there's probably a really stupidly simple solution that I'm missing. For now, I can just change it to instantaneous movement, but it looks really jerky. Can someone help?

In this case, you might want to add a keyListener yo your component.
yourComponent.addKeyListener(new KeyAdapter () { // Possibly your Frame
#Override // Overrides the keyPressed event
public void keyPressed(KeyEvent e) {
if ( e == YOUR_KEY_CODE ) {
for( int var = 0; var < yourDistance; var ++ ){
yourSpriteComponent.x += 1;
try{
Thread.sleep(yourTimeInMilliSec);
} catch( Exception e ){
// Your catch block here
}
}
}
}
});
Where YOUR_KEY_CODE is the key that the user needs to be pressed in order to execute the for() loop. Key Codes can be found in javadoc

Key Pressing partially working

I've been trying to do some kind of autoclicker and have the following code in java:
import java.awt.event.*;
import java.awt.*;
class keyStroke {
public void Execute() throws AWTException {
int n = 0;
while(n < 100){
Robot r = new Robot();
r.delay(1000);
r.keyPress(KeyEvent.VK_1);
r.keyRelease(KeyEvent.VK_1);
++n;
}
}
}
It works pretty fine clicking the key 1, but, it doesn't work in some games.
It looks to be working only on chatbox and accessing to it (enter key), but aside from that, nothing else works (like using a skill or moving).
Then, I decided to also try in C++, with the following code
#include <iostream>
#include <windows.h>
#include <cstdlib>
using namespace std;
void SendKey (char Vk){
char VkKey = VkKeyScan(Vk);
keybd_event(VkKey, 0, 0, 0);
keybd_event(VkKey, 0, KEYEVENTF_KEYUP, 0);
}
int main(){
while(true){
SendKey('1');
Sleep(1000);
}
}
And the same thing happens.
What am U doing wrong? If the keypress doesn't work for this case I have to find something else?

I know from experience that some game input doesn't use an event based structure. Some games only check once every frame if a key is pressed. This means that your chance of pressing the key at that exact moment are zero.
Scripting utilities such as the logitech keyboard scripting tool face a similar problem and there it helps to have a delay between press and release.
Aside: chat windows usually have to use an input event as typing would be almost impossible if key presses are only registered once per frame.

How do I set the position of the mouse in Java?

I'm doing some Swing GUI work with Java, and I think my question is fairly straightforward; How does one set the position of the mouse?

As others have said, this can be achieved using Robot.mouseMove(x,y). However this solution has a downfall when working in a multi-monitor situation, as the robot works with the coordinate system of the primary screen, unless you specify otherwise.
Here is a solution that allows you to pass any point based global screen coordinates:
public void moveMouse(Point p) {
GraphicsEnvironment ge =
GraphicsEnvironment.getLocalGraphicsEnvironment();
GraphicsDevice[] gs = ge.getScreenDevices();
// Search the devices for the one that draws the specified point.
for (GraphicsDevice device: gs) {
GraphicsConfiguration[] configurations =
device.getConfigurations();
for (GraphicsConfiguration config: configurations) {
Rectangle bounds = config.getBounds();
if(bounds.contains(p)) {
// Set point to screen coordinates.
Point b = bounds.getLocation();
Point s = new Point(p.x - b.x, p.y - b.y);
try {
Robot r = new Robot(device);
r.mouseMove(s.x, s.y);
} catch (AWTException e) {
e.printStackTrace();
}
return;
}
}
}
// Couldn't move to the point, it may be off screen.
return;
}

You need to use Robot
This class is used to generate native system input events for the purposes of test automation, self-running demos, and other applications where control of the mouse and keyboard is needed. The primary purpose of Robot is to facilitate automated testing of Java platform implementations.
Using the class to generate input events differs from posting events to the AWT event queue or AWT components in that the events are generated in the platform's native input queue. For example, Robot.mouseMove will actually move the mouse cursor instead of just generating mouse move events...

Robot.mouseMove(x,y)

Check out the Robot class.

The code itself is the following:
char escCode = 0x1B;
System.out.print(String.format("%c[%d;%df",escCode,row,column));
This code is incomplete by itself, so I recommend placing it in a method and calling it something like 'positionCursor(int row, int column)'.
Here is the code in full (method and code):
void positionCursor(int row, int column) {
char escCode = 0x1B;
System.out.print(String.format("%c[%d;%df",escCode,row,column));
}