TranslateAnimation works by "pulling" the View in one direction by a specified amount. You can set where to start this "pulling" and where to end.
TranslateAnimation(fromXDelta, toXDelta, fromYDelta, toYDelta);
fromXDelta set the offset of the starting position of the movement in the X axis.
fromXDelta = 0 //no offset.
fromXDelta = 300 //the movement starts at 300px to the right.
fromXDelta = -300 //the movement starts at 300px to the left
toXDelta defines the offset ending position of the movement in the X axis.
toXDelta = 0 //no offset.
toXDelta = 300 //the movement ends at 300px to the right.
toXDelta = -300 //the movement ends at 300px to the left.
If the width of your text is greater that the module of the difference between fromXDelta and toXDelta, the text won't be able to totaly and compeltely move within the screen.
Example
Let's assume our screen size is 320x240 pxs. We have a TextView with a text that has 700px width and we wish to create an animation that "pulls" the text so that we can see the end of the phrase.
(screen)
+---------------------------+
|<----------320px---------->|
| |
|+---------------------------<<<< X px >>>>
movement<-----|| some TextView with text that goes out...
|+---------------------------
| unconstrained size 700px |
| |
| |
+---------------------------+
+---------------------------+
| |
| |
<<<< X px >>>>---------------------------+|
movement<----- some TextView with text that goes out... ||
---------------------------+|
| |
| |
| |
+---------------------------+
First we set fromXDelta = 0 so that the movement doesn't have a starting offset. Now we need to figure the toXDelta value. To achieve the desired effect we need to "pull" the text the exact same px that it spans out of the screen. (in the scheme is represented by <<<< X px >>>>) Since our text has 700 width, and the visible area is 320px (screen width) we set:
tXDelta = 700 - 320 = 380
And how do we figure the Screen Width and the text Width?
Code
Taking the Zarah Snippet as a starting point:
/**
* @param view The Textview or any other view we wish to apply the movement
* @param margin A margin to take into the calculation (since the view
* might have any siblings in the same "row")
*
**/
public static Animation scrollingText(View view, float margin){
Context context = view.getContext(); //gets the context of the view
// measures the unconstrained size of the view
// before it is drawn in the layout
view.measure(View.MeasureSpec.UNSPECIFIED,
View.MeasureSpec.UNSPECIFIED);
// takes the unconstrained wisth of the view
float width = view.getMeasuredWidth();
// gets the screen width
float screenWidth = ((Activity) context).getWindowManager().getDefaultDisplay().getWidth();
// perfrms the calculation
float toXDelta = width - (screenWidth - margin);
// sets toXDelta to 0 if the text width is smaller that the screen size
if (toXDelta < 0) {toXDelta = 0; } else { toXDelta = 0 - toXDelta;}
// Animation parameters
Animation mAnimation = new TranslateAnimation(0, toXDelta, 0, 0);
mAnimation.setDuration(15000);
mAnimation.setRepeatMode(Animation.RESTART);
mAnimation.setRepeatCount(Animation.INFINITE);
return mAnimation;
}
There might be easier ways to perform this, but this works for every view you can think of and is reusable. It is specially usefull if you want to animate a TextView in a ListView without breaking the enabled/onFocus abilities of the textView. It also scrolls continuously even if the View is not focused.
