Android自定义控件实现带文字提示的SeekBar

public class IndicatorSeekBar extends AppCompatSeekBar {

 // 画笔
 private Paint mPaint;
 // 进度文字位置信息
 private Rect mProgressTextRect = new Rect();
 // 滑块按钮宽度
 private int mThumbWidth = dp2px(50);
 // 进度指示器宽度
 private int mIndicatorWidth = dp2px(50);
 // 进度监听
 private OnIndicatorSeekBarChangeListener mIndicatorSeekBarChangeListener;

 public IndicatorSeekBar(Context context) {
 this(context, null);
 }

 public IndicatorSeekBar(Context context, AttributeSet attrs) {
 this(context, attrs, R.attr.seekBarStyle);
 }

 public IndicatorSeekBar(Context context, AttributeSet attrs, int defStyleAttr) {
 super(context, attrs, defStyleAttr);
 init();
 }

 private void init() {
 mPaint = new TextPaint();
 mPaint.setAntiAlias(true);
 mPaint.setColor(Color.parseColor("#00574B"));
 mPaint.setTextSize(sp2px(16));

 // 如果不设置padding，当滑动到最左边或最右边时，滑块会显示不全
 setPadding(mThumbWidth / 2, 0, mThumbWidth / 2, 0);

 // 设置滑动监听
 this.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
 @Override
 public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
 // NO OP
 }

 @Override
 public void onStartTrackingTouch(SeekBar seekBar) {
 if (mIndicatorSeekBarChangeListener != null) {
  mIndicatorSeekBarChangeListener.onStartTrackingTouch(seekBar);
 }
 }

 @Override
 public void onStopTrackingTouch(SeekBar seekBar) {
 if (mIndicatorSeekBarChangeListener != null) {
  mIndicatorSeekBarChangeListener.onStopTrackingTouch(seekBar);
 }
 }
 });
 }

 @Override
 protected synchronized void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 String progressText = getProgress() + "%";
 mPaint.getTextBounds(progressText, 0, progressText.length(), mProgressTextRect);

 // 进度百分比
 float progressRatio = (float) getProgress() / getMax();
 // thumb偏移量
 float thumbOffset = (mThumbWidth - mProgressTextRect.width()) / 2 - mThumbWidth * progressRatio;
 float thumbX = getWidth() * progressRatio + thumbOffset;
 float thumbY = getHeight() / 2f + mProgressTextRect.height() / 2f;
 canvas.drawText(progressText, thumbX, thumbY, mPaint);

 if (mIndicatorSeekBarChangeListener != null) {
 float indicatorOffset = getWidth() * progressRatio - (mIndicatorWidth - mThumbWidth) / 2 - mThumbWidth * progressRatio;
 mIndicatorSeekBarChangeListener.onProgressChanged(this, getProgress(), indicatorOffset);
 }
 }

 /**
 * 设置进度监听
 *
 * @param listener OnIndicatorSeekBarChangeListener
 */
 public void setOnSeekBarChangeListener(OnIndicatorSeekBarChangeListener listener) {
 this.mIndicatorSeekBarChangeListener = listener;
 }

 /**
 * 进度监听
 */
 public interface OnIndicatorSeekBarChangeListener {
 /**
 * 进度监听回调
 *
 * @param seekBar SeekBar
 * @param progress 进度
 * @param indicatorOffset 指示器偏移量
 */
 public void onProgressChanged(SeekBar seekBar, int progress, float indicatorOffset);

 /**
 * 开始拖动
 *
 * @param seekBar SeekBar
 */
 public void onStartTrackingTouch(SeekBar seekBar);

 /**
 * 停止拖动
 *
 * @param seekBar SeekBar
 */
 public void onStopTrackingTouch(SeekBar seekBar);
 }

 /**
 * dp转px
 *
 * @param dp dp值
 * @return px值
 */
 public int dp2px(float dp) {
 return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp,
 getResources().getDisplayMetrics());
 }

 /**
 * sp转px
 *
 * @param sp sp值
 * @return px值
 */
 private int sp2px(float sp) {
 return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, sp,
 getResources().getDisplayMetrics());
 }
}

@Override
protected synchronized void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 String progressText = getProgress() + "%";
 mPaint.getTextBounds(progressText, 0, progressText.length(), mProgressTextRect);

 // 进度百分比
 float progressRatio = (float) getProgress() / getMax();
 // thumb偏移量
 float thumbOffset = (mThumbWidth - mProgressTextRect.width()) / 2 - mThumbWidth * progressRatio;
 float thumbX = getWidth() * progressRatio + thumbOffset;
 float thumbY = getHeight() / 2f + mProgressTextRect.height() / 2f;
 canvas.drawText(progressText, thumbX, thumbY, mPaint);

 if (mIndicatorSeekBarChangeListener != null) {
 float indicatorOffset = getWidth() * progressRatio - (mIndicatorWidth - mThumbWidth) / 2 - mThumbWidth * progressRatio;
 mIndicatorSeekBarChangeListener.onProgressChanged(this, getProgress(), indicatorOffset);
 }
}

// 【总宽度 * 进度百分比 -（指示器宽度 - 滑块宽度）/ 2 - 滑块宽度 * 进度百分比】
float indicatorOffset = getWidth() * progressRatio - (mIndicatorWidth - mThumbWidth) / 2 - mThumbWidth * progressRatio;
mIndicatorSeekBarChangeListener.onProgressChanged(this, getProgress(), indicatorOffset);

public class MainActivity extends AppCompatActivity {

 private TextView tvIndicator;
 private IndicatorSeekBar indicatorSeekBar;
 private Paint mPaint = new Paint();

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 tvIndicator = findViewById(R.id.tv_indicator);
 indicatorSeekBar = findViewById(R.id.indicator_seek_bar);

 initData();
 }

 private void initData() {
 final LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) tvIndicator.getLayoutParams();
 indicatorSeekBar.setOnSeekBarChangeListener(new IndicatorSeekBar.OnIndicatorSeekBarChangeListener() {
  @Override
  public void onProgressChanged(SeekBar seekBar, int progress, float indicatorOffset) {
  String indicatorText = progress + "%";
  tvIndicator.setText(indicatorText);
  params.leftMargin = (int) indicatorOffset;
  tvIndicator.setLayoutParams(params);
  }

  @Override
  public void onStartTrackingTouch(SeekBar seekBar) {
  tvIndicator.setVisibility(View.VISIBLE);
  }

  @Override
  public void onStopTrackingTouch(SeekBar seekBar) {
  tvIndicator.setVisibility(View.INVISIBLE);
  }
 });
 }
}

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