Hello All.
Iv'e been writing a simple drawing App as homework for university.
Drawing works fine, but the canvas should also be cleared when the App
is coming back from the background. When switching bach i get the
following:
IllegalThreadStateException: Thread already started.
at java.lang.Thread (Thread.java: 1284)
and directed to line 134 in my code:
class Panel extends SurfaceView implements SurfaceHolder.Callback {
//some code
@Override
public void surfaceCreated(SurfaceHolder holder) {
synchronized (_thread) {
if (!_thread.getRunning()) {
_thread.setRunning(true);
_thread.start(); /////←←←← LINE 134
!!!
}
}
}
Thanks for your helping !!
Amit from Berlin
**** HERE IS MY COMPLETE CODE : ******** (All is in one file)
package de.fu.amit;
import java.util.ArrayList;
import java.util.Random;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class SimpleDraw extends Activity {
private final int MAX_WIDTH = 20;
private DrawingThread _thread;
private Panel panel;
private int backgroundColor;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//second parameter defines the background color
backgroundColor = new Random().nextInt();
panel = new Panel(this, backgroundColor);
setContentView(panel);
}
@Override
protected void onStop() {
panel.clearPanel();
super.onStop();
}
@Override
protected void onRestart() {
super.onRestart();
}
class Panel extends SurfaceView implements SurfaceHolder.Callback {
private Line startedLine;
private Paint linePaint;
private int backgroundColor;
private ArrayList<Line> lines = new ArrayList<Line>();
public Panel(Context context, int backgroundColor) {
super(context);
getHolder().addCallback(this);
_thread = new DrawingThread(getHolder(), this);
setFocusable(true);
this.backgroundColor = backgroundColor;
}
protected void clearPanel(){
lines = new ArrayList<Line>();
}
private void pickColors() {
Random r = new Random();
linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
linePaint.setColor(r.nextInt());
linePaint.setStrokeWidth(Math.abs(r.nextInt()) %
MAX_WIDTH);
linePaint.setStyle(Style.STROKE);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.i("Simple-Draw:", event.toString() + " x:" +
event.getX()
+ " y:" + event.getY());
synchronized (_thread.getSurfaceHolder()) {
if (event.getAction() == MotionEvent.ACTION_UP)
{
return true;
} else if (event.getAction() ==
MotionEvent.ACTION_DOWN) {
/**
* on a finger-down even, new color
will be picked for the
* next line means, if a line has
already been started it
* will keep it's color and the new
color will be valid for
* the lines to come.
*/
pickColors();
}
if (startedLine == null ||
startedLine.isComplete()) {
/**
* creating a new line in case no line
has been started.
* with the created class attribute
linePaint
*/
startedLine = new Line(event.getX(),
event.getY(),
linePaint);
} else { // we have a non completed line, so we
complete it
startedLine.setEnd(event.getX(),
event.getY());
// and add to the list
lines.add(startedLine);
startedLine =
startedLine.getContinue(linePaint);
}
return true;
}
}
@Override
public void onDraw(Canvas canvas) {
canvas.drawColor(backgroundColor);
/*
* Bitmap bitmap; Coordinates coords;
*/
for (Line line : lines) {
canvas.drawLine(line.x_start, line.y_start,
line.x_end,
line.y_end, line.getPaint());
}
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int
width,
int height) {
// TODO Auto-generated method stub
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
synchronized (_thread) {
if (!_thread.getRunning()) {
_thread.setRunning(true);
_thread.start();
}
}
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// simply copied from sample application LunarLander:
// we have to tell thread to shut down & wait for it to
finish, or
// else
// it might touch the Surface after we return and
explode
boolean retry = true;
_thread.setRunning(false);
while (retry) {
try {
_thread.join();
retry = false;
} catch (InterruptedException e) {
Log.e("caught an exception:
surfaceDestroyed()",e.toString());
}
}
}
}
class DrawingThread extends Thread {
private SurfaceHolder _surfaceHolder;
private Panel _panel;
private boolean _run = false;
public DrawingThread(SurfaceHolder surfaceHolder, Panel panel) {
_surfaceHolder = surfaceHolder;
_panel = panel;
}
public SurfaceHolder getSurfaceHolder() {
return _surfaceHolder;
}
public boolean getRunning() {
return _run;
}
public void setRunning(boolean run) {
_run = run;
}
@Override
public void run() {
Canvas c;
while (_run) {
c = null;
try {
c = _surfaceHolder.lockCanvas(null);
synchronized (_surfaceHolder) {
_panel.onDraw(c);
}
} finally {
// do this in a finally so that if an
exception is thrown
// during the above, we don't leave the
Surface in an
// inconsistent state
if (c != null) {
_surfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
}
class Line {
private Float x_start;
private Float y_start;
private Float x_end;
private Float y_end;
private Paint paint;
protected Line(Float x, Float y, Paint paint) {
this.x_start = x;
this.y_start = y;
this.paint = paint;
}
public Paint getPaint() {
return paint;
}
protected Line(Float x_start, Float y_start, Float x_end, Float
y_end,
Paint paint) {
this.x_start = x_start;
this.y_start = y_start;
this.x_end = x_end;
this.y_end = y_end;
this.paint = paint;
}
protected void setEnd(Float x, Float y) {
this.x_end = x;
this.y_end = y;
}
protected Line getContinue(Paint paint) {
return new Line(x_end, y_end, paint);
}
protected boolean isComplete() {
return ((x_end != null) && (y_end != null) && (x_start
!= null) &&
(y_start != null));
}
@Override
public String toString() {
return "line: Start(" + x_start.toString() + ","
+ y_start.toString() + ") End: (" +
x_end.toString() + ","
+ y_end.toString() + ")";
}
}
}
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