这篇文章将为大家详细讲解有关Android如何实现自定义字母选择侧边栏，小编觉得挺实用的，因此分享给大家做个参考，希望大家阅读完这篇文章后可以有所收获。
具体内容如下
LetterSideBar.java
package com.zb.customview.widgets;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.text.TextUtils;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import androidx.annotation.Nullable;
import com.zb.customview.R;
public class LetterSideBar extends View {
private Paint mPaint;
private int color, selectedColor;
private float textSize, spacing;
private String mChoosing = "Z";
private OnLetterSelectedListener listener;
private int width, height;
private String[] LETTERS = new String[] {"#", "A", "B", "C", "D", "E", "F",
"G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V",
"W", "X", "Y", "Z"};
public interface OnLetterSelectedListener {
//空表示取消选中
void onSelected(String letter);
}
public void setOnLetterSelectedListener(OnLetterSelectedListener listener) {
this.listener = listener;
}
public LetterSideBar(Context context) {
this(context, null);
}
public LetterSideBar(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
if(null != attrs) {
TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.LetterSideBar);
color = ta.getColor(R.styleable.LetterSideBar_LetterSideBar_textColor, Color.BLACK);
selectedColor = ta.getColor(R.styleable.LetterSideBar_LetterSideBar_textSelectedColor, Color.RED);
textSize = ta.getDimensionPixelSize(R.styleable.LetterSideBar_LetterSideBar_textSize, sp2px(12));
spacing = ta.getDimensionPixelSize(R.styleable.LetterSideBar_LetterSideBar_spacing, dp2px(5));
ta.recycle();
}
init();
}
private void init() {
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setColor(color);
mPaint.setTextSize(textSize);
}
@Override
protected void onDraw(Canvas canvas) {
drawText(canvas);
drawSelectedText(canvas, mChoosing);
}
private void drawText(Canvas canvas) {
mPaint.setColor(color);
for (int i=0; i<LETTERS.length; i++) {
drawLetterAt(canvas, i, LETTERS[i]);
}
}
private void drawSelectedText(Canvas canvas, String selected) {
if(TextUtils.isEmpty(selected))
return;
mPaint.setColor(selectedColor);
int position = -1;
for(int i=0; i<LETTERS.length; i++) {
if(selected.equals(LETTERS[i])) {
position = i;
break;
}
}
if(position < 0 || position >= LETTERS.length)
return;
drawLetterAt(canvas, position, selected);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_MOVE:
float x = event.getX();
float y = event.getY();
if(isTouchInsideView(x, y)) {
//触摸在控件内
int position = caculatePosition(y);
if(position >= 0 && position < LETTERS.length) {
//合规位置
String letter = LETTERS[position];
if(!letter.equals(mChoosing)) { //与选中的不符 去刷新控件
mChoosing = letter;
performListener(mChoosing);
invalidate();
}
} else {
//不合规位置
if(null != mChoosing) {
mChoosing = null;
performListener(mChoosing);
invalidate();
}
}
} else if(null != mChoosing) { //点击事件不在view内部
mChoosing = null;
performListener(mChoosing);
invalidate();//触摸在view之外 取消选中
}
return true;
default:
if(mChoosing != null) {
mChoosing = null;
performListener(mChoosing);
invalidate();
}
break;
}
return super.onTouchEvent(event);
}
private void performListener(String letter) {
if(null != listener)
listener.onSelected(letter);
}
private boolean isTouchInsideView(float x, float y) {
//左右可以适当判断在控件内
if(x >= 0 && x <= width && y >= getPaddingTop() && y < height)
return true;
return false;
}
/**
* 计算触摸的位置
* @param y
* @return
*/
private int caculatePosition(float y) {
float heightWithOutPadding = height - getPaddingTop() - getPaddingBottom();
float eachElementHeight = heightWithOutPadding / LETTERS.length;
y -= getPaddingTop();
int position = (int) (y / eachElementHeight);
return position;
}
private void drawLetterAt(Canvas canvas, int position, String letter) {
float heightForEach = ((height * 1f - getPaddingTop() - getPaddingBottom())
- (LETTERS.length - 1) * spacing) / LETTERS.length;
float spacingInUp = spacing * (position - 1);
if(spacingInUp < 0)
spacingInUp = 0;
float currentTop = getPaddingTop() + (heightForEach * position) + spacingInUp;
float currentBottom = currentTop + heightForEach;
Paint.FontMetrics fmi = mPaint.getFontMetrics();
float x = (width - getPaddingLeft() - getPaddingRight() - mPaint.measureText(letter)) / 2f + getPaddingLeft();
float baseLine = (fmi.descent + Math.abs(fmi.ascent)) / 2f - fmi.descent;
float y = (currentBottom + currentTop) / 2f + baseLine;
canvas.drawText(letter, 0, 1, x, y, mPaint);
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
if(changed) {
width = getWidth();
height = getHeight();
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int textWidth = (int) (getPaddingLeft() + getPaddingRight() + mPaint.measureText("A"));
Rect textBounds = new Rect();
mPaint.getTextBounds("A", 0, 1, textBounds);
int singleTextHeight = textBounds.height();
int totalHeight = (int) (27f * singleTextHeight + 26f * spacing) + getPaddingBottom() + getPaddingTop();//26个字母+1个#
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(widthMeasureSpec);
int specWidth = MeasureSpec.getSize(widthMeasureSpec);
int specHeight = MeasureSpec.getSize(widthMeasureSpec);
int realWidth, realHeight;
if(widthMode == MeasureSpec.EXACTLY) {
realWidth = specWidth;
} else {
realWidth = textWidth;
}
if(heightMode == MeasureSpec.EXACTLY) {
realHeight = specHeight;
} else {
realHeight = totalHeight;
}
setMeasuredDimension(realWidth, realHeight);
}
protected int dp2px(int dp) {
return (int) (getContext().getResources().getDisplayMetrics().density * dp + 0.5);
}
protected int sp2px(int sp) {
return (int) (getContext().getResources().getDisplayMetrics().scaledDensity * sp + 0.5);
}
}attrs.xml
<declare-styleable name="LetterSideBar"> <attr name="LetterSideBar_textColor" format="color"/> <attr name="LetterSideBar_textSelectedColor" format="color"/> <attr name="LetterSideBar_textSize" format="dimension"/> <attr name="LetterSideBar_spacing" format="dimension"/> </declare-styleable>
layout.xml
<com.zb.customview.widgets.LetterSideBar android:id="@+id/letterSideBar" android:layout_width="wrap_content" android:layout_height="wrap_content" app:LetterSideBar_textSize="14sp" app:LetterSideBar_textColor="#FFFFFF" android:padding="10dp" app:LetterSideBar_textSelectedColor="#FF0000" app:LetterSideBar_spacing="2dp" app:layout_constraintRight_toRightOf="parent" app:layout_constraintTop_toTopOf="parent" app:layout_constraintBottom_toBottomOf="parent" android:background="#A4A4A4"/>
代码中使用
sideBar.setOnLetterSelectedListener(new LetterSideBar.OnLetterSelectedListener() {
@Override
public void onSelected(String letter) {
if(TextUtils.isEmpty(letter)) {
P.p("取消选中");
letterTxt.setVisibility(View.GONE);
} else {
P.p("选中" + letter);
letterTxt.setText(letter);
letterTxt.setVisibility(View.VISIBLE);
}
}
});关于“Android如何实现自定义字母选择侧边栏”这篇文章就分享到这里了，希望以上内容可以对大家有一定的帮助，使各位可以学到更多知识，如果觉得文章不错，请把它分享出去让更多的人看到。
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