Develop Reference

When scroll the ListView, why onLayout method not called in ListView?

Write a Custom ListView like:
public class MyListView extends ListView {
public MyListView(Context context) {
super(context);
}
public MyListView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyListView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
#Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
Log.d("onLayout","onLayout=====");
}
}
As I know, when the layout attribute of view has changed, in order to apply the change ( invalide() or requestLayout() )，its parent's onLayout method should be called and layout its children.
So when I scroll the ListView, the layout attribute of its child view has changed, but onLayout doesn't called at all. Why?

Finally I realized relayout a ViewGroup don't need always call onLayout()/layout() method.There are many ways to change views position in ViewGroup,but each way must call onDraw() to write the changed position in FrameBuffer in order to show it in Screen.(Please tell whether I'm wrong with this)
In ListView,I had debug the source code,and when scroll ListView, the stack trace is:
`
trackMotionScroll:5023, AbsListView (android.widget)
scrollIfNeeded:3424, AbsListView (android.widget)
startScrollIfNeeded:3352, AbsListView (android.widget)
onTouchMove:3793, AbsListView (android.widget)
onTouchEvent:3651, AbsListView (android.widget)
dispatchTouchEvent:9294, View (android.view)
in trackMotionScroll,it will call ViewGroup#offsetChildrenTopAndBottom(incrementalDeltaY)
public void offsetChildrenTopAndBottom(int offset) {
final int count = mChildrenCount;
final View[] children = mChildren;
boolean invalidate = false;
for (int i = 0; i < count; i++) {
final View v = children[i];
v.mTop += offset;
v.mBottom += offset;
if (v.mRenderNode != null) {
invalidate = true;
v.mRenderNode.offsetTopAndBottom(offset);
}
}
if (invalidate) {
invalidateViewProperty(false, false);
}
notifySubtreeAccessibilityStateChangedIfNeeded();
}
This will cause the reLayout of ListView.
So I got a conclusion,you don't need obey the framework's measure()–layout()–draw() procedure,but only change view's layout attribute and invalidate,it will also change view's layout.
And I guess ListView dispense with layout() when scroll will improve its efficiency

Android ListView full scroll to the top while using clipToPadding="false"

I have this litle custom ListView witch is actually a 'ListView' with some call backs. When i dynamically change padding when starting the Activity (Height of the Toolbar), Items dose not respond to padding, and i have to scroll to the top some how.
This is my ListWiew.
<somesustom.cutom.ObservableListView
android:id="#+id/listview"
android:clipToPadding="false"
android:theme="#style/ListView"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />
So the question is How to scroll fully to the top from code?
So i have found the solution
first i deleted android:clipToPadding="false" from xml.
then i configured my ObservableListView like this
public class ObservableListView extends ListView {
private boolean clipPadding = true;
public ObservableListView(Context context) {
this(context, null, 0);
setScrollListner();
}
public ObservableListView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
setScrollListner();
}
public ObservableListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setScrollListner();
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if(clipPadding) /// this is the trick, if clip to padding is true, then set selection 0
setSelection(0);
}
public void setScrollListner()
{
clipPadding = true;
super.setOnScrollListener(new OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if(clipPadding && scrollState == OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
setClipToPadding(false);
clipPadding = false; // if ii begin to scroll clipPadding
// turns to false and onMeasure set selection not being called.
}
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
}
});
}
}
Not sure if this method wouldn't work if i change padding on button click i guess. But in my case, where i set padding from ViewTreeObserver.OnGlobalLayoutListener this works quite well.

You can try one of two things or both:
listview.smoothScrollToPosition(0);
or
listview.setSelection(0):

How to add a custom view in another custom view in Android?

I want to create a custom view which should be added in another custom view.
The second view will be a container, so it should be able to contain the first view as its child.
For creating this views I am extending ViewGroup & LinearLayout classes.
Child view class is NodeView
public class NodeView extends LinearLayout
{
private final static String TAG = "NodeView";
private ImageView ivTop;
private ImageView ivBottom;
private Context myContext;
public NodeView(Context context, AttributeSet attrs)
{
super(context, attrs);
this.myContext = context;
setOrientation(LinearLayout.VERTICAL);
setGravity(Gravity.CENTER);
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
inflater.inflate(R.layout.view_test_multi, this, true);
ivTop = (ImageView) getChildAt(0);
ivBottom = (ImageView) getChildAt(2);
ivTop.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View v)
{
Toast.makeText(myContext, "Top Clicked", Toast.LENGTH_SHORT).show();
}
});
ivBottom.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View v)
{
Toast.makeText(myContext, "Bottom Clicked", Toast.LENGTH_SHORT).show();
}
});
}
#Override
protected void onDraw(Canvas canvas)
{
super.onDraw(canvas);
}
public NodeView(Context context)
{
this(context, null);
}
}
& the container class is TreeViewGroup
public class TreeViewGroup extends ViewGroup
{
private static final String TAG = "CustomTreeNodeView";
NodeView nodeView;
public TreeViewGroup(Context context, AttributeSet attrs, int defStyleAttr)
{
super(context, attrs, defStyleAttr);
nodeView = new NodeView(getContext());
addView(nodeView);
}
public TreeViewGroup(Context context, AttributeSet attrs)
{
this(context, attrs, 0);
}
public TreeViewGroup(Context context)
{
this(context, null, 0);
}
#Override
protected void onDraw(Canvas canvas)
{
super.onDraw(canvas);
}
#Override
protected void onLayout(boolean changed, int l, int t, int r, int b)
{
}
}
& xml layout for node view is view_test_multi.xml
<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android" >
<ImageView
android:layout_width="15dp"
android:layout_height="15dp"
android:layout_centerVertical="true"
android:src="#drawable/point_grey" />
<ImageView
android:layout_width="35dp"
android:layout_height="35dp"
android:layout_centerVertical="true"
android:src="#drawable/point_red" />
<ImageView
android:layout_width="15dp"
android:layout_height="15dp"
android:layout_centerVertical="true"
android:src="#drawable/point_grey" />
</merge>
My activity's layout is activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:custom="http://schemas.android.com/apk/res/com.ab1209.testcustom"
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.ab1209.testcustom.view.TreeViewGroup
android:id="#+id/activity_main_custom_tree_node_view"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>
MainActivity class is
**public class MainActivity extends Activity
{
TreeViewGroup treeNodeView;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
treeNodeView = (TreeViewGroup) findViewById(R.id.activity_main_custom_tree_node_view);
}
}**
When I run the app I don't see the NodeView added in main View. Am I doing the right thing if not please tell me how can I make it working?

To create a custom ViewGroup, the only method you need to override is
onLayout. The onLayout is triggered after the ViewGroup itself has
finished laying itself out inside its own container ViewGroup and is
now responsible for laying out its children. It should call the layout
method on all of its children to now position and size them (the left
and top parameters will determine the child view’s x and y and the
right and bottom will determine its width (right – left) and height
(top-bottom).
So your TreeViewGroup code will look like :
#Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int count = getChildCount();
for (int i = 0; i < count; i++) {
View child = getChildAt(i);
if (child.getVisibility() != GONE) {
ViewGroup.LayoutParams lp = (ViewGroup.LayoutParams) child
.getLayoutParams();
int childLeft = 0;
int childTop = 0;
child.layout(childLeft, childTop,
childLeft + child.getMeasuredWidth(),
childTop + child.getMeasuredHeight());
}
}
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
measureChildren(widthMeasureSpec, heightMeasureSpec);
int measuredWidth = 200; // Calculate the height
int measuredHeight = 200; // Calculate the width
setMeasuredDimension(measuredWidth, measuredHeight);
}
Refer this link http://arpitonline.com/2012/07/01/creating-custom-layouts-for-android/

Android getting exact scroll position in ListView

I'd like to get the exact, pixel position of the ListView scroll.
And no, I am not referring to the first visible position.
Is there a way to achieve this?

Okay, I found a workaround, using the following code:
View c = listview.getChildAt(0);
int scrolly = -c.getTop() + listview.getFirstVisiblePosition() * c.getHeight();
The way it works is it takes the actual offset of the first visible list item and calculates how far it is from the top of the view to determine how much we are "scrolled into" the view, so now that we know that we can calculate the rest using the regular getFirstVisiblePosition method.

Saarraz1's answer will only work if all the rows in the listview are of the same height and there's no header (or it is also the same height as the rows).
Note that once the rows disappear at the top of the screen you don't have access to them, as in you won't be able to keep track of their height. This is why you need to save those heights (or accumulated heights of all). My solution requires keeping a Dictionary of heights per index (it is assumed that when the list is displayed the first time it is scrolled to the top).
private Dictionary<Integer, Integer> listViewItemHeights = new Hashtable<Integer, Integer>();
private int getScroll() {
View c = listView.getChildAt(0); //this is the first visible row
int scrollY = -c.getTop();
listViewItemHeights.put(listView.getFirstVisiblePosition(), c.getHeight());
for (int i = 0; i < listView.getFirstVisiblePosition(); ++i) {
if (listViewItemHeights.get(i) != null) // (this is a sanity check)
scrollY += listViewItemHeights.get(i); //add all heights of the views that are gone
}
return scrollY;
}

Simplest idea I could come up with was to extend ListView and expose the "computeVerticalScrollOffset" which is protected by default, then use "com.your.package.CustomListView" in your xml layouts.
public class CustomListView extends ListView {
public CustomListView(Context context) {
super(context);
}
public CustomListView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public CustomListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
#Override
public int computeVerticalScrollOffset() {
return super.computeVerticalScrollOffset();
}
}

First Declare your int variable for hold the position.
int position = 0;
then add scrollListener to your ListView,
listView.setOnScrollListener(new OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
position = firstVisibleItem;
}
});
Then after getting new data or any changes in your data that time you need to set the listview current position
listView.setSelection(position);
I have used after setup my adapter , works fine for me..

If anyone else found this in Google while looking for a way to track relative scroll offsets in an OnScrollListener - that is, change in Y since the last call to the listener - here's a Gist showing how to calculate that.

I know I'm late to the party but I felt like sharing my solution to this problem. I have a ListView and I was trying to find how much I have scrolled in order to scroll something else relative to it and cause a parallax effect. Here's my solution:
public abstract class OnScrollPositionChangedListener implements AbsListView.OnScrollListener {
int pos;
int prevIndex;
int prevViewPos;
int prevViewHeight;
#Override
public void onScroll(AbsListView v, int i, int vi, int n) {
try {
View currView = v.getChildAt(0);
int currViewPos = Math.round(currView.getTop());
int diffViewPos = prevViewPos - currViewPos;
int currViewHeight = currView.getHeight();
pos += diffViewPos;
if (i > prevIndex) {
pos += prevViewHeight;
} else if (i < prevIndex) {
pos -= currViewHeight;
}
prevIndex = i;
prevViewPos = currViewPos;
prevViewHeight = currViewHeight;
} catch (Exception e) {
e.printStackTrace();
} finally {
onScrollPositionChanged(pos);
}
}
#Override public void onScrollStateChanged(AbsListView absListView, int i) {}
public abstract void onScrollPositionChanged(int scrollYPosition);
}
I created my own OnScrollListener where the method onScrollPositionChanged will be called every time onScroll gets called. But this method will have access to the calculated value representing the amount that the ListView has been scrolled.
To use this class, you can setOnClickListener to a new OnScrollPositionChangedListener and override the onScrollPositionChanged method.
If you need to use the onScroll method for other stuff then you can override that too but you need to call super.onScroll to get onScrollPositionChanged working correctly.
myListView.setOnScrollListener(
new OnScrollPositionChangedListener() {
#Override
public void onScroll(AbsListView v, int i, int vi, int n) {
super.onScroll(v, i, vi, n);
//Do your onScroll stuff
}
#Override
public void onScrollPositionChanged(int scrollYPosition) {
//Enjoy having access to the amount the ListView has scrolled
}
}
);

in addition to #jaredpetker answer.
ListView is not holding all the items in its scroll, so u need to operate only "visible" part of list. When you scroll down top items are shifted out and pushed as new item views. Thats how convertedView is came from (it's not empty item to fill, it's shifted item that is out of "visible" part of list. So u need to know how many items was before visible part multiply them with ListItemHeight and add headerHeight, thes how you can get real absolute offset in scroll. If u got not header, position 0 will be listItem, so you can simplify absoluteY += pos*listItemHeight;
public class CustomListView extends ListView {
private int listItemHeight = 140;
private int headerHeight = 200;
public CustomListView(Context context) {
super(context);
}
public CustomListView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public CustomListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
#Override
public int computeVerticalScrollOffset() {
final int y = super.computeVerticalScrollOffset();
int absoluteY = y;
int pos = getFirstVisiblePosition();
if(pos > 0){
absoluteY += (pos-1)*listItemHeight+header‌​Height;
}
//use absoluteY
return y;
}

I had faced the similar problem, That I wanted to place the Vertical Seekbar at current scrolled value of ListView. So I have my own solution like this.
First Create Class
public abstract class OnScrollPositionChangedListener implements AbsListView.OnScrollListener {
int pos;
public int viewHeight = 0;
public int listHeight = 0;
#Override
public void onScroll(AbsListView v, int i, int vi, int n) {
try {
if(viewHeight==0) {
viewHeight = v.getChildAt(0).getHeight();
listHeight = v.getHeight();
}
pos = viewHeight * i;
} catch (Exception e) {
e.printStackTrace();
} finally {
onScrollPositionChanged(pos);
}
}
#Override public void onScrollStateChanged(AbsListView absListView, int i) {}
public abstract void onScrollPositionChanged(int scrollYPosition);
}
Then use it in Main Activity like this.
public class MainActivity extends AppCompatActivity {
SeekBar seekBar;
ListView listView;
OnScrollPositionChangedListener onScrollPositionChangedListener = new OnScrollPositionChangedListener() {
#Override
public void onScroll(AbsListView v, int i, int vi, int n) {
super.onScroll(v, i, vi, n);
//Do your onScroll stuff
}
#Override
public void onScrollPositionChanged(int scrollYPosition) {
//Enjoy having access to the amount the ListView has scrolled
seekBar.setProgress(scrollYPosition);
}
};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
seekBar = (SeekBar) findViewById(R.id.mySeekBar);
listView = (ListView) findViewById(R.id.listView);
final String[] values = new String[]{"Android List View",
"Adapter implementation",
"Simple List View In Android",
"Create List View Android",
"Android Example",
};
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, android.R.id.text1, values);
listView.setAdapter(adapter);
listView.setOnScrollListener(onScrollPositionChangedListener);
seekBar.postDelayed(new Runnable() {
#Override
public void run() {
seekBar.setMax((onScrollPositionChangedListener.viewHeight * values.length) - onScrollPositionChangedListener.listHeight);
}
}, 1000);
seekBar.setEnabled(false);
}
}
in App Gradle
compile 'com.h6ah4i.android.widget.verticalseekbar:verticalseekbar:0.7.0'
In XML Layout
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="#+id/activity_main"
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="com.centsol.charexamples.MainActivity">
<ListView
android:id="#+id/listView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fadeScrollbars="false"
android:scrollbars="none"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true">
</ListView>
<!-- This library requires pair of the VerticalSeekBar and VerticalSeekBarWrapper classes -->
<com.h6ah4i.android.widget.verticalseekbar.VerticalSeekBarWrapper
android:layout_width="wrap_content"
android:layout_alignParentRight="true"
android:layout_height="match_parent">
<com.h6ah4i.android.widget.verticalseekbar.VerticalSeekBar
android:id="#+id/mySeekBar"
android:layout_width="0dp"
android:progressDrawable="#drawable/progress"
android:thumb="#drawable/thumb"
android:layout_height="0dp"
android:splitTrack="false"
app:seekBarRotation="CW90" /> <!-- Rotation: CW90 or CW270 -->
</com.h6ah4i.android.widget.verticalseekbar.VerticalSeekBarWrapper>
<View
android:layout_width="1dp"
android:visibility="visible"
android:layout_alignParentRight="true"
android:layout_marginTop="16dp"
android:layout_marginRight="2.5dp"
android:layout_marginBottom="16dp"
android:background="#android:color/black"
android:layout_height="match_parent" />
</RelativeLayout>
background xml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >
<solid android:color="#android:color/transparent"/>
</shape>
fill xml
<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >
<solid android:color="#android:color/transparent" />
</shape>
progress xml
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
<item
android:id="#android:id/background"
android:drawable="#drawable/background"/>
<item android:id="#android:id/progress">
<clip android:drawable="#drawable/fill" />
</item>
</layer-list>
thumb xml
<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="oval" >
<solid android:color="#android:color/holo_red_dark" />
<size
android:height="5dp"
android:width="5dp" />
</shape>

How can i view a video inside a videoview at some specific position?

I am currently trying to implement a videoview that will show a video on a specific position. I can show a fullscreen video with no problem. However whenever i try to show that video inside a frame( a little rectangle for example ) I can only show a part of video in that view. I couldn't fit the video into that view.
I already look for lots of links about scaling a video in android, however I couldnt find any way to do this. Any help about that issue will be helpful.
What i am using is i have 2 different classes. One of them is my video activity class and other one is a helper class:
public class VideoViewCustom extends VideoView {
private int mForceHeight = 0;
private int mForceWidth = 0;
public VideoViewCustom(Context context) {
super(context);
}
public VideoViewCustom(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public VideoViewCustom(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public void setDimensions(int w, int h) {
this.mForceHeight = h;
this.mForceWidth = w;
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
setMeasuredDimension(mForceWidth, mForceHeight);
}
}
That class help me to set dimensions of videoview correctly, however i couldnt make video fit into that region. I mean I couldn't scale the video to fit into that region. I dont know whether or not android is autoscaling into given dimensions but i couldnt do it.

May this will help you...
public void onMeasure(int width, int height)
{
getHolder().setFixedSize(width, height);
forceLayout();
setMeasuredDimension(width, height);
invalidate();
}
...and try a RelativeLayout
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<VideoView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentTop="true"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentLeft="true"/>
</RelativeLayout>

I think you have to create a ViewGroup where you can implements onLayout() method.
Here you can set the position of your views directly calling the layout() method for each one of them.
Example:
ViewGroup vg = new ViewGroup(this) {
#Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int x = getMeasuredWidth();
int y = getMeasuredHeight();
for (int i = 0; i < vg.getChildCount(); i++) {
if(vg.getChildAt(i) instanceof TextView){
vg.getChildAt(i).layout(...);//and so on...
}
}
}
};
Hope helping!!