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Simple line indicator for ViewPager
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import android.content.Context; | |
import android.database.DataSetObserver; | |
import android.graphics.Canvas; | |
import android.graphics.Color; | |
import android.graphics.Paint; | |
import android.graphics.Rect; | |
import android.util.AttributeSet; | |
import android.view.View; | |
import androidx.annotation.NonNull; | |
import androidx.annotation.Nullable; | |
import androidx.viewpager.widget.PagerAdapter; | |
import androidx.viewpager.widget.ViewPager; | |
public class LinePagerIndicator extends View implements ViewPager.OnPageChangeListener, ViewPager.OnAdapterChangeListener { | |
private int barWidth; | |
private ViewPager pager; | |
private Paint paint; | |
private IndicatorObserver observer; | |
private int left; | |
public LinePagerIndicator(Context context) { | |
super(context); | |
init(); | |
} | |
public LinePagerIndicator(Context context, @Nullable AttributeSet attrs) { | |
super(context, attrs); | |
init(); | |
} | |
public LinePagerIndicator(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { | |
super(context, attrs, defStyleAttr); | |
init(); | |
} | |
public void setViewPager(ViewPager pager) { | |
if (this.pager != null && this.pager.getAdapter() != null) { | |
this.pager.getAdapter().unregisterDataSetObserver(observer); | |
this.pager.removeOnAdapterChangeListener(this); | |
this.pager.removeOnPageChangeListener(this); | |
} | |
this.pager = pager; | |
updatePagerInfo(true); | |
} | |
@Override | |
public void draw(Canvas canvas) { | |
super.draw(canvas); | |
Rect rect = new Rect(); | |
rect.left = left; | |
rect.top = 0; | |
rect.bottom = getMeasuredHeight(); | |
rect.right = left + barWidth; | |
canvas.drawRect(rect, paint); | |
} | |
@Override | |
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { | |
int desiredWidth = getSuggestedMinimumWidth() + getPaddingLeft() + getPaddingRight(); | |
int desiredHeight = getSuggestedMinimumHeight() + getPaddingTop() + getPaddingBottom(); | |
setMeasuredDimension(measureDimension(desiredWidth, widthMeasureSpec), measureDimension(desiredHeight, heightMeasureSpec)); | |
updatePagerInfo(false); | |
} | |
@Override | |
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { | |
left = Math.round(barWidth * positionOffset) + (barWidth * position); | |
invalidate(); | |
} | |
@Override | |
public void onPageSelected(int position) { | |
} | |
@Override | |
public void onPageScrollStateChanged(int state) { | |
} | |
@Override | |
public void onAdapterChanged(@NonNull ViewPager viewPager, @Nullable PagerAdapter oldAdapter, @Nullable PagerAdapter newAdapter) { | |
updatePagerInfo(false); | |
} | |
@Override | |
protected void onLayout(boolean changed, int left, int top, int right, int bottom) { | |
super.onLayout(changed, left, top, right, bottom); | |
updatePagerInfo(false); | |
} | |
private void init() { | |
paint = new Paint(); | |
paint.setColor(Color.WHITE); | |
paint.setStyle(Paint.Style.FILL); | |
this.observer = new IndicatorObserver(); | |
left = 0; | |
} | |
private void updatePagerInfo(boolean addListeners) { | |
if (pager != null && pager.getAdapter() != null) { | |
if (addListeners) { | |
pager.getAdapter().registerDataSetObserver(observer); | |
pager.addOnAdapterChangeListener(this); | |
pager.addOnPageChangeListener(this); | |
} | |
int itemCount = pager.getAdapter().getCount() == 0 ? 1 : pager.getAdapter().getCount(); | |
barWidth = getMeasuredWidth() / itemCount; | |
} else { | |
barWidth = getMeasuredWidth(); | |
} | |
invalidate(); | |
} | |
private int measureDimension(int desiredSize, int measureSpec) { | |
int result; | |
int specMode = MeasureSpec.getMode(measureSpec); | |
int specSize = MeasureSpec.getSize(measureSpec); | |
if (specMode == MeasureSpec.EXACTLY) { | |
result = specSize; | |
} else { | |
result = desiredSize; | |
if (specMode == MeasureSpec.AT_MOST) { | |
result = Math.min(result, specSize); | |
} | |
} | |
return result; | |
} | |
private class IndicatorObserver extends DataSetObserver { | |
@Override | |
public void onChanged() { | |
updatePagerInfo(false); | |
} | |
@Override | |
public void onInvalidated() { | |
updatePagerInfo(false); | |
} | |
} | |
} |
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