Develop Reference

How to capture part of a ScrollView as its content is scrolling?

After extending the ScrollView class I was able to easily be notified of the scrolling in realtime.
Now I need to capture the content of this scrollview in a very specific part.
Let's say I want to capture the top of the screen (matching parent width and a defined height, like 100dp). But only the content of the ScrollView and not the rest, if there is anything else on the top but not as part of the ScrollView.
I tried using on the scrollview :
setDrawingCacheEnabled(true);
getDrawingCache(true);
setDrawingCacheEnabled(false);
Then I tried to crop so that I get the part I want :
Bitmap.createBitmap(complete, 0, 0, width, height);
Results are very far from what I want to achieve and performance are very very poor and at some point I would get either a SIGENV or getDrawingCache(true) tries to use a recycled bitmap...
So how can I easily capture the content in the desired area without too much performance hit ?
Note: this process must be done as I am scrolling the content, so inside ScrollView's onScrollChanged(final int x, final int y).
Thanks !

Since the problem was fun I implemented it, it seems to work fine. I guess that you are recreating a Bitmap each time that's why goes slow.
The idea is like this, you create an area in the ScrollView that you want to copy (see Rect cropRect and Bitmap screenshotBitmap), it's full width and you just need to set the height. The view automatically set a scroll listener on itself and on every scroll it will copy that area. Note that setDrawingCacheEanbled(true) is called just once when the view is instantiated, it basically tells the view that you will call getDrawingCache(), which will return the Bitmap on which the view is drawing itself. It then copy the area of interest on screenshotBitmap and that's the Bitmap that you might want to use.
ScreenshottableScrollView.java
package com.example.lelloman.screenshottablescrollview;
import android.annotation.TargetApi;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.Rect;
import android.os.Build;
import android.util.AttributeSet;
import android.view.ViewTreeObserver;
import android.widget.ScrollView;
/**
* Created by lelloman on 16-2-16.
*/
public class ScreenshottableScrollView extends ScrollView implements ViewTreeObserver.OnScrollChangedListener {
public interface OnNewScreenshotListener {
void onNewScreenshot(Bitmap bitmap);
}
private Bitmap screenshotBitmap = null;
private Canvas screenshotCanvas = null;
private int screenshotHeightPx = 0;
private OnNewScreenshotListener listener = null;
private Rect cropRect;
private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
public ScreenshottableScrollView(Context context) {
super(context);
init();
}
public ScreenshottableScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public ScreenshottableScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
#TargetApi(Build.VERSION_CODES.LOLLIPOP)
public ScreenshottableScrollView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
init();
}
private void init(){
setDrawingCacheEnabled(true);
getViewTreeObserver().addOnScrollChangedListener(this);
}
public void setOnNewScreenshotListener(OnNewScreenshotListener listener){
this.listener = listener;
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
if(screenshotHeightPx != 0)
makeScrenshotBitmap(w,h);
}
public void setScreenshotHeightPx(int q){
screenshotHeightPx = q;
makeScrenshotBitmap(getWidth(), getHeight());
}
private void makeScrenshotBitmap(int width, int height){
if(screenshotBitmap != null) screenshotBitmap.recycle();
if(width == 0 || height == 0) return;
screenshotBitmap = Bitmap.createBitmap(width, screenshotHeightPx, Bitmap.Config.ARGB_8888);
screenshotCanvas = new Canvas(screenshotBitmap);
cropRect = new Rect(0,0,width,screenshotHeightPx);
}
#Override
public void onScrollChanged() {
if(listener == null) return;
Bitmap bitmap = getDrawingCache();
screenshotCanvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
screenshotCanvas.drawBitmap(bitmap,cropRect, cropRect,paint);
listener.onNewScreenshot(screenshotBitmap);
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.lelloman.screenshottablescrollview.MainActivity">
<com.example.lelloman.screenshottablescrollview.ScreenshottableScrollView
android:id="#+id/scrollView"
android:layout_weight="1"
android:layout_width="match_parent"
android:layout_height="0dp">
<TextView
android:id="#+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</com.example.lelloman.screenshottablescrollview.ScreenshottableScrollView>
<View
android:layout_width="match_parent"
android:layout_height="20dp"
android:background="#ff000000"/>
<ImageView
android:id="#+id/imageView"
android:layout_width="match_parent"
android:layout_height="100dp" />
</LinearLayout>
MainActivity.java
package com.example.lelloman.screenshottablescrollview;
import android.graphics.Bitmap;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.Random;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
StringBuilder builder = new StringBuilder();
Random random = new Random();
String AB = "abcdefghijklmnopqrstuvwxyz ";
for(int i=0;i<100;i++){
builder.append("\n\n"+Integer.toString(i)+"\n\n");
for(int j =0;j<1000;j++){
builder.append(AB.charAt(random.nextInt(AB.length())));
}
}
((TextView) findViewById(R.id.textView)).setText(builder.toString());
final ImageView imageView = (ImageView) findViewById(R.id.imageView);
ScreenshottableScrollView scrollView = (ScreenshottableScrollView) findViewById(R.id.scrollView);
scrollView.setScreenshotHeightPx((int) (getResources().getDisplayMetrics().density * 100));
scrollView.setOnNewScreenshotListener(new ScreenshottableScrollView.OnNewScreenshotListener() {
#Override
public void onNewScreenshot(Bitmap bitmap) {
Log.d("MainActivity","onNewScreenshot");
imageView.setImageBitmap(bitmap);
}
});
}
}

Android drawing just get a black view

I am following this tutorial: http://danielnadeau.blogspot.ca/2012/01/android-canvas-beginners-tutorial.html
When I look at things in the "Graphical Layout" tab in Eclipse, I see the expected result (a red square in the center of the display), but when I actually run the app, I just get a large black rectangle, and I can't seem to figure out why. I've searched some posts, but have not found an answer that seems to apply to my situation.
MainActivity.java
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
activity_mail.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<com.hintonworks.cantstop.CustomView
android:layout_width="match_parent"
android:layout_height="200dp"
android:id="#+id/my_view" />
</RelativeLayout>
CustomView.java
package com.hintonworks.cantstop;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class CustomView extends SurfaceView implements SurfaceHolder.Callback {
public CustomView (Context context) {
super(context);
}
public CustomView (Context context, AttributeSet attrs) {
super(context);
}
#Override
public void onDraw (Canvas canvas) {
int dCenter = 40; //Distance from center in px, NOT in dp
int centerX = (int)(getWidth()/2);
int centerY = (int)(getHeight()/2);
Paint paint = new Paint();
paint.setColor(Color.RED); //The square will draw in the color blue now
Rect rect = new Rect(centerX-dCenter, centerY-dCenter, centerX+dCenter, centerY+dCenter);
canvas.drawRect(rect, paint);
}
#Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {}
#Override
public void surfaceCreated(SurfaceHolder holder) {
setWillNotDraw(false); //Allows us to use invalidate() to call onDraw()
postInvalidate();
}
#Override
public void surfaceDestroyed(SurfaceHolder holder) {}
}
Thanks for any insight. This is my stab at using the canvas, until now I have been using drawable resources.

How to Draw line between two views in android?

I want to draw a line between two views how it could possible using canvas

Its simple Take one linearLayout for it between two views
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="1dp"
android:background="#285A8C" > //Give Color As u want
</LinearLayout>

Thanks every one i got the following solution for this I am using three layouts the middle layout i used for canvas and draw points in that canvas on button on click event
DrawView.java
package demo.example;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;
public class DrawView extends View {
Paint paint = new Paint();
float [][] points;
public DrawView(Context context, float[][] points2, int k) {
super(context);
paint.setColor(Color.BLUE);
paint.setStrokeWidth(5);
this.points=points2;
}
#Override
public void onDraw(Canvas canvas) {
for(int i=0;i<points.length;i++)
{
canvas.drawLine(points[i][0],points[i][1],points[i][2],points[i][3], paint);
}
}
}
get points using following click listener
public class listener implements OnClickListener
{
int i;
listener(int k)
{
this.i=k;
}
public void onClick(View v)
{
for(int k=0;k<match1.length;k++)
{
if(match1[k].isClickable()==false)
{
if(match1[k].getId()==match2[i].getId())
{
points[k][0]=match1[k].getLeft();
points[k]1]=match1[k].getTop()+30+linearLayout2.getTop(); points[k][2]=200;
points[k][3]=match2[i].getTop()+30+linearLayout2.getTop();
match1[k].setCompoundDrawablesWithIntrinsicBounds(null, null,null,null);
match2[i].setCompoundDrawablesWithIntrinsicBounds(getResources().getDrawable(R.drawable.bubble), null,null, null);
Toast.makeText(getBaseContext(),points[0]+"-"+points[1]+"-"+points[2]+"-"+points[3],Toast.LENGTH_SHORT).show();
ViewGroup.LayoutParams lp = new LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT);
drawView = new DrawView(getBaseContext(),points,k);
linearLayout2.addView(drawView);
}
}
}
}
}

How to draw lines over ImageView on Android?

I am trying to develop a simple map application, which will display a map in the screen.
When the user moves the cursor on screen, I want to display 2 perpendicular lines over my map. I had tried many examples to get an idea for that, but unfortunately, didn't succeed.
How can I make this?
And as one previous questionhere I had tried. but didn't get the answer. Can anyone guide me?
My main.xml is as following:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<LinearLayout android:layout_width="wrap_content"
android:layout_height="wrap_content">
<ImageView android:id="#+id/main_imagemap"
android:src="#drawable/worldmap"
android:clickable="true"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
</LinearLayout>
And my activity file(i had just started it..)
import android.app.Activity;
import android.os.Bundle;
import android.widget.ImageView;
public class LineMapActivity extends Activity
{
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ImageView map_image = (ImageView)findViewById(R.id.main_imagemap);
}
}
And as in that link, i had also added MyImageView.
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.widget.ImageView;
public class MyImageView extends ImageView
{
public MyImageView(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);
canvas.drawLine(0, 0, 20, 20, p);
super.onDraw(canvas);
}
}
Now how can i add this MyImageView to my app?

Finally I figured out a solution. It's a simple program which draws a line over an Image.
Here is my main.xml file (com.ImageDraw.MyImageView is my custom view, code below):
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<LinearLayout android:layout_width="wrap_content"
android:layout_height="wrap_content">
<com.ImageDraw.MyImageView android:id="#+id/main_imagemap"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
</LinearLayout>
And here is the main activity:
import android.app.Activity;
import android.os.Bundle;
public class MyActivity extends Activity
{
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
and this is my custom image view (MyImageView):
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class MyImageView extends SurfaceView implements SurfaceHolder.Callback
{
private CanvasThread canvasthread;
public MyImageView(Context context) {
super(context);
getHolder().addCallback(this);
canvasthread = new CanvasThread(getHolder(), this);
setFocusable(true);
}
public MyImageView(Context context, AttributeSet attrs)
{
super(context,attrs);
getHolder().addCallback(this);
canvasthread = new CanvasThread(getHolder(), this);
setFocusable(true);
}
protected void onDraw(Canvas canvas) {
Log.d("ondraw", "ondraw");
Paint p = new Paint();
Bitmap mapImg = BitmapFactory.decodeResource(getResources(), R.drawable.mybitmap);
canvas.drawColor(Color.BLACK);
canvas.drawBitmap(mapImg, 0, 0, null);
p.setColor(Color.RED);
canvas.drawLine(0, 0, 100, 100, p);
}
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
}
public void surfaceCreated(SurfaceHolder holder) {
canvasthread.setRunning(true);
canvasthread.start();
}
public void surfaceDestroyed(SurfaceHolder holder) {
boolean retry = true;
canvasthread.setRunning(false);
while (retry)
{
try
{
canvasthread.join();
retry = false;
}
catch (InterruptedException e) {
// TODO: handle exception
}
}
}
}
And finally here is my CanvasThread:
import android.graphics.Canvas;
import android.view.SurfaceHolder;
public class CanvasThread extends Thread
{
private SurfaceHolder surfaceHolder;
private MyImageView myImageView;
private boolean run = false;
public CanvasThread(SurfaceHolder s, MyImageView m)
{
surfaceHolder = s;
myImageView = m;
}
public void setRunning(boolean r)
{
run = r;
}
public void run()
{
Canvas c;
while(run)
{
c=null;
try
{
c= surfaceHolder.lockCanvas(null);
synchronized (surfaceHolder) {
myImageView.onDraw(c);
}
}
finally
{
if(c!=null)
{
surfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
}
You can find more details in this tutorial

Error you are getting because you are trying to casting ImageView object to MyImageView object.

Just fix the xml to include your object instead of an imageview like so (note that com.your.package.MyImageView should be the full package name of the package containing your class and then the class name)
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<LinearLayout android:layout_width="wrap_content"
android:layout_height="wrap_content">
<com.your.package.MyImageView android:id="#+id/main_imagemap"
android:src="#drawable/worldmap"
android:clickable="true"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
</LinearLayout>

android - for loop drawing circles not working?

I am trying to draw multiple circles from an array and it is throwing a "force close" when I try to run the code. Any ideas here?
package com.adam.PlaySound;
import android.app.Activity;
import android.media.MediaPlayer;
import android.net.Uri;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;
public class ButtonPress extends Activity {
/** Called when the activity is first created. */
int numPlayers = 3;
boolean toggle = true;
LinearLayout parent;
Button button;
TextView text;
TextView text2;
DisplayMetrics dm = new DisplayMetrics();
MediaPlayer mediaPlayer[] = new MediaPlayer[numPlayers];
//this array is a placeholder for the loops in a cluster
//essentially this array will be populated through a database
//based on which cluster someone is within
//and the region arrays will be populated by the same database
String soundFiles[] = {"drums_1.mp3", "lead.mp3", "strings.mp3"};
public LoopRegion region[] = new LoopRegion[numPlayers];
float regionX[] = {20, 80, 150};
float regionY[] = {20, 200, 350};
int regionR[] = {50, 80, 100};
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//setContentView(R.id.view1);
parent = (LinearLayout) findViewById(R.id.parent);
button = (Button) findViewById(R.id.button1);
text = (TextView) findViewById(R.id.text);
text2 = (TextView) findViewById(R.id.text2);
parent.setOnTouchListener(Motion);
button.setOnClickListener(on_off);
for (int i = 0; i < numPlayers; i++){
String path = "http://soundclusters.adamlaskowitz.com/uploads/" + soundFiles[i];
mediaPlayer[i] = new MediaPlayer();
//mediaPlayer[i] = MediaPlayer.create(ButtonPress.this, R.raw.drums_2);
mediaPlayer[i] = MediaPlayer.create(ButtonPress.this, Uri.parse(path));
mediaPlayer[i].setLooping(true);
}
for (int i = 0; i < numPlayers; i++){
region[i] = new LoopRegion(this,regionX[i],regionY[i],regionR[i]);
parent.addView(region[i]);
}
getWindowManager().getDefaultDisplay().getMetrics(dm);
}
This is the LoopRegion class.
package com.adam.PlaySound;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.view.View;
/*This class will create a circle region for
*each loop within a cluster */
public class LoopRegion extends View {
private float x;
private float y;
private int r;
private final Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
public LoopRegion(Context context, float x, float y, int r) {
super(context);
mPaint.setColor(0xFFFF0000);
this.x = x;
this.y = y;
this.r = r;
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawCircle(x, y, r, mPaint);
}
public void setCoordinate(float mx, float my){
this.x = mx;
this.y = my;
//this.r = 300;
}
}
And this is the XML
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="#+id/parent"
>
<TextView android:id="#+id/text"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Not Playing"
/>
<TextView android:id="#+id/text2"
android:layout_height="wrap_content"
android:text="Location" android:layout_width="wrap_content"
/>
<Button android:text="Sound On/Off"
android:id="#+id/button1" android:layout_width="fill_parent" android:layout_height="wrap_content">
</Button>
<!-- <View android:id="#+id/view1"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
</View>-->
</LinearLayout>
Thanks in advance!

My guess is that your LoopRegion views have layout parameters set to FILL_PARENT and the first one pushes the others off the screen. It would help to see the code for how a LoopRegion is created, and perhaps the XML for the parent LinearLayout.