分析:一条线段,在标题之间移动,移动到两个标题中间时长度最长,反之,移动到标题正下方时最短。也就是说,该线段在水平位移的同时,长度也随之变化,接近左边标题时,长度与位移成正相关,接近右边标题时,长度与位移成负相关。这本质上是两个二元一次方程,求系数和常数项的问题。起点终点都有值,可解。
import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.util.Log;
import android.util.SparseArray;
import android.util.SparseIntArray;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.LinearLayout;
import android.widget.TextView;
import androidx.viewpager.widget.ViewPager;
import com.sony.dtv.moocnavbar.R;
import java.util.List;
public class MoocNavBar extends LinearLayout {
private List<String> titles;
private Context context;
private View indictor;
private SparseIntArray toLeftMap = new SparseIntArray();//title到left的距离
private int defaultPos = 0; //默认pos
private int minW = 15; //指示器的最小width
public MoocNavBar(Context context) {
this(context, null);
}
public MoocNavBar(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public MoocNavBar(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
this.context = context;
setOrientation(VERTICAL);
}
public void setTitle(List<String> title) {
this.titles = title;
//titles
LinearLayout titleContainer = new LinearLayout(context);
titleContainer.setOrientation(HORIZONTAL);
LayoutParams titleLP = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
titleContainer.setLayoutParams(titleLP);
fillTitle(titleContainer, title);
addView(titleContainer);
//indictor
indictor = new View(context);
LinearLayout.LayoutParams indictorLP = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
indictorLP.bottomMargin = 10;
indictorLP.width = minW;
indictorLP.height = 6;
indictor.setLayoutParams(indictorLP);
indictor.setBackgroundResource(R.drawable.nav_indictor_bg);
addView(indictor);
}
private void fillTitle(final LinearLayout titleContainer, List<String> titles) {
for (int i = 0; i < titles.size(); i++) {
String s = titles.get(i);
final TextView titleItemView = new TextView(context);
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
titleItemView.setLayoutParams(params);
titleItemView.setText(s);
titleItemView.setTextColor(Color.BLACK);
titleItemView.setPadding(30, 10, 30, 10);
final int finalI = i;
titleItemView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
titleItemView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
int left = titleItemView.getWidth() / 2 + titleItemView.getLeft();
Log.e("TAG", finalI + " : " + left);
toLeftMap.append(finalI, left);
if (finalI == defaultPos) {
//
moveIndictor(finalI, 0);
}
}
});
titleContainer.addView(titleItemView);
}
}
public void setViewPager(ViewPager viewPager) {
viewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
moveIndictor(position, positionOffset);
}
});
}
//根据页面切换过程,改变指示器位置和大小
private void moveIndictor(int position, float positionOffset) {
//在某两个page之间滑动时,获取对应的两个title的中点位置
int l1 = toLeftMap.get(position);
int l2 = toLeftMap.get(position + 1);
//两点间距
int datL = l2 - l1;
//指示器中点应该在哪个位置
int middle = (int) (l1 + datL * positionOffset);
//指示器宽度最大值
int maxW = datL / 3 * 2;
//指示器最大最小值差距
int datW = maxW - minW;
//实际宽度
int realW;
if (positionOffset <= 0.5) {
realW = (int) (minW + 2 * positionOffset * datW);
} else {
realW = (int) (minW + (1 - positionOffset) * 2 * datW);
}
//设置左右位置
indictor.setLeft(middle - realW / 2);
indictor.setRight(middle + realW / 2);
}
}
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