ScrollTextView - scrolling TextView for Android
找了很就终于在国外一网站上找到一个Scroller的例子,为了日后方便查阅,在博客上记录以下。
Here are the source codes.
The key points are:
- setHorizontallyScrolling() and use android.widget.Scroller to make the text scroll;
- Use the attached TextPaint of the TextView to measure the length of the text in pixel;
- setSingleLine() and setEllipsize(null) to make the text not wrapped and ellipsized;
- Override computeScroll() to restart the scrolling when finished
Here are the source codes.
代码
/*************************************************************************/
package com.dirtybear.android;
import android.content.Context;
import android.graphics.Rect;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.view.animation.LinearInterpolator;
import android.widget.Scroller;
import android.widget.TextView;
public class ScrollTextView extends TextView {
// scrolling feature
private Scroller mSlr;
// milliseconds for a round of scrolling
private int mRndDuration = 250;
// the X offset when paused
private int mXPaused = 0;
// whether it's being paused
private boolean mPaused = true;
/*
* constructor
*/
public ScrollTextView(Context context) {
this(context, null);
}
/*
* constructor
*/
public ScrollTextView(Context context, AttributeSet attrs) {
this(context, attrs, android.R.attr.textViewStyle);
}
/*
* constructor
*/
public ScrollTextView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// customize the TextView
setSingleLine();
setEllipsize(null);
setVisibility(INVISIBLE);
}
/**
* begin to scroll the text from the original position
*/
public void startScroll() {
// begin from the very right side
mXPaused = -1 * getWidth();
// assume it's paused
mPaused = true;
resumeScroll();
}
/**
* resume the scroll from the pausing point
*/
public void resumeScroll() {
if (!mPaused)
return;
// Do not know why it would not scroll sometimes
// if setHorizontallyScrolling is called in constructor.
setHorizontallyScrolling(true);
// use LinearInterpolator for steady scrolling
mSlr = new Scroller(this.getContext(), new LinearInterpolator());
setScroller(mSlr);
int scrollingLen = calculateScrollingLen();
int distance = scrollingLen - (getWidth() + mXPaused);
int duration = (new Double(mRndDuration * distance * 1.00000
/ scrollingLen)).intValue();
setVisibility(VISIBLE);
mSlr.startScroll(mXPaused, 0, distance, 0, duration);
mPaused = false;
}
/**
* calculate the scrolling length of the text in pixel
*
* @return the scrolling length in pixels
*/
private int calculateScrollingLen() {
TextPaint tp = getPaint();
Rect rect = new Rect();
String strTxt = getText().toString();
tp.getTextBounds(strTxt, 0, strTxt.length(), rect);
int scrollingLen = rect.width() + getWidth();
rect = null;
return scrollingLen;
}
/**
* pause scrolling the text
*/
public void pauseScroll() {
if (null == mSlr)
return;
if (mPaused)
return;
mPaused = true;
// abortAnimation sets the current X to be the final X,
// and sets isFinished to be true
// so current position shall be saved
mXPaused = mSlr.getCurrX();
mSlr.abortAnimation();
}
@Override
/*
* override the computeScroll to restart scrolling when finished so as that
* the text is scrolled forever
*/
public void computeScroll() {
super.computeScroll();
if (null == mSlr) return;
if (mSlr.isFinished() && (!mPaused)) {
this.startScroll();
}
}
public int getRndDuration() {
return mRndDuration;
}
public void setRndDuration(int duration) {
this.mRndDuration = duration;
}
public boolean isPaused() {
return mPaused;
}
}
/*************************************************************************/
package com.dirtybear.android;
import android.content.Context;
import android.graphics.Rect;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.view.animation.LinearInterpolator;
import android.widget.Scroller;
import android.widget.TextView;
public class ScrollTextView extends TextView {
// scrolling feature
private Scroller mSlr;
// milliseconds for a round of scrolling
private int mRndDuration = 250;
// the X offset when paused
private int mXPaused = 0;
// whether it's being paused
private boolean mPaused = true;
/*
* constructor
*/
public ScrollTextView(Context context) {
this(context, null);
}
/*
* constructor
*/
public ScrollTextView(Context context, AttributeSet attrs) {
this(context, attrs, android.R.attr.textViewStyle);
}
/*
* constructor
*/
public ScrollTextView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// customize the TextView
setSingleLine();
setEllipsize(null);
setVisibility(INVISIBLE);
}
/**
* begin to scroll the text from the original position
*/
public void startScroll() {
// begin from the very right side
mXPaused = -1 * getWidth();
// assume it's paused
mPaused = true;
resumeScroll();
}
/**
* resume the scroll from the pausing point
*/
public void resumeScroll() {
if (!mPaused)
return;
// Do not know why it would not scroll sometimes
// if setHorizontallyScrolling is called in constructor.
setHorizontallyScrolling(true);
// use LinearInterpolator for steady scrolling
mSlr = new Scroller(this.getContext(), new LinearInterpolator());
setScroller(mSlr);
int scrollingLen = calculateScrollingLen();
int distance = scrollingLen - (getWidth() + mXPaused);
int duration = (new Double(mRndDuration * distance * 1.00000
/ scrollingLen)).intValue();
setVisibility(VISIBLE);
mSlr.startScroll(mXPaused, 0, distance, 0, duration);
mPaused = false;
}
/**
* calculate the scrolling length of the text in pixel
*
* @return the scrolling length in pixels
*/
private int calculateScrollingLen() {
TextPaint tp = getPaint();
Rect rect = new Rect();
String strTxt = getText().toString();
tp.getTextBounds(strTxt, 0, strTxt.length(), rect);
int scrollingLen = rect.width() + getWidth();
rect = null;
return scrollingLen;
}
/**
* pause scrolling the text
*/
public void pauseScroll() {
if (null == mSlr)
return;
if (mPaused)
return;
mPaused = true;
// abortAnimation sets the current X to be the final X,
// and sets isFinished to be true
// so current position shall be saved
mXPaused = mSlr.getCurrX();
mSlr.abortAnimation();
}
@Override
/*
* override the computeScroll to restart scrolling when finished so as that
* the text is scrolled forever
*/
public void computeScroll() {
super.computeScroll();
if (null == mSlr) return;
if (mSlr.isFinished() && (!mPaused)) {
this.startScroll();
}
}
public int getRndDuration() {
return mRndDuration;
}
public void setRndDuration(int duration) {
this.mRndDuration = duration;
}
public boolean isPaused() {
return mPaused;
}
}
/*************************************************************************/
Issues to be fixed:
- Do not know why it would not scroll sometimes if setHorizontallyScrolling is called in constructor;
- The scrolling is not smooth enough. Maybe it's because of the single thread model of Android UI;
Tested on:
Windows XP
Android SDK 1.0 rc2
Android Emulator 1.0
Android Debug Bridge version 1.0.20