紅橙Darren視訊筆記 自定義RatingBar touch事件學習 dp轉px listener監聽

效果圖：

一 需求分析

我們需要實現評分的控制元件 那麼主要有幾步
1.繪製出評分控制元件
2.響應使用者的觸控改變星星數
3.控制元件發生星星變化時通知監聽者

二 自定義屬性

需要屬性：
星星總數
選中星星的圖片id
空白星星的圖片id
星星之間的間隔

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="CustomRatingBar">
        <attr name="pressedStar" format="reference" />
        <attr name="normalStar" format="reference" />
        <attr name="starNumber" format="integer" />
        <attr name="starGap" format="dimension" />
    </declare-styleable>
</resources>

三 建立自定義View檔案 獲取自定義屬性 初始化各種變數

    private static final String TAG = "CustomRatingBar";
    private Paint starPaint;
    private Bitmap starPressed, starNormal;
    private int starNumberSum = 0, starGap = 0, currentPressedStarIndex = -1;
    private TouchListener touchListener;


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

    public CustomRatingBar(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CustomRatingBar(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(attrs, context);

    }

    private void init(AttributeSet attrs, Context context) {
        TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.CustomRatingBar);
        int normalStarRes = array.getResourceId(R.styleable.CustomRatingBar_normalStar, -1);
        int pressedStarRes = array.getResourceId(R.styleable.CustomRatingBar_pressedStar, -1);
        starGap = (int) array.getDimension(R.styleable.CustomRatingBar_starGap, dp2px(10));
        if (normalStarRes == -1 || pressedStarRes == -1) {
            throw new RuntimeException("請指定資源id pressedStar normalStar！ ");
        }
        starPressed = BitmapFactory.decodeResource(getResources(), pressedStarRes);
        starNormal = BitmapFactory.decodeResource(getResources(), normalStarRes);
        starNumberSum = array.getInt(R.styleable.CustomRatingBar_starNumber, 2);
        starPaint = new Paint();
        starPaint.setAntiAlias(true);//抗鋸齒
        starPaint.setDither(true);//防抖動
        array.recycle();
    }

    private float dp2px(int dp) {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, getResources().getDisplayMetrics());
    }

四 測量控制元件

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int height = starPressed.getHeight() + getPaddingBottom() + getPaddingTop();
        int width = starPressed.getWidth() * starNumberSum + starGap * (starNumberSum - 1) + getPaddingStart() + getPaddingEnd();
        setMeasuredDimension(width, height);
    }

五 繪製自定義控制元件

    @Override
    protected void onDraw(Canvas canvas) {
        for (int i = 0; i < starNumberSum; i++) {
            int startX = getPaddingStart() + (starNormal.getWidth() + starGap) * i;
            int startY = getPaddingTop();
            if (i <= currentPressedStarIndex) {
                canvas.drawBitmap(starPressed, startX, startY, starPaint);
            } else {
                canvas.drawBitmap(starNormal, startX, startY, starPaint);
            }
        }
    }

六 觸控事件

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //Log.d(TAG, "onTouchEvent: " + event.getAction() + " event.getX() " + event.getX() + " event.getY() " + event.getY());
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
            case MotionEvent.ACTION_MOVE:
                //判斷Y座標落在有效區間
                if (event.getY() < getPaddingTop() || event.getY() > (starNormal.getHeight() + getPaddingTop())) {
                    return true;
                }
                //判斷X座標落在有效區間
                if (event.getX() < getPaddingStart() || event.getX() > (starNormal.getWidth() * starNumberSum + starGap * (starNumberSum - 1) + getPaddingStart())) {
                    return true;
                }
                //判斷落在第幾個星星
                int starNum = (int) ((event.getX() - getPaddingStart()) / (starNormal.getWidth() + starGap));
                if (currentPressedStarIndex != starNum) {
                    Log.d(TAG, "onTouchEvent: starNum" + starNum);
                    currentPressedStarIndex = starNum;
                    invalidate();
                }
                break;
            case MotionEvent.ACTION_UP:
                if (touchListener != null) {
                    touchListener.actionUp(currentPressedStarIndex);
                }
                break;
        }
        return true;//不消費事件
    }

七 補充 dp轉px listener增加

1.增加listener

    public void setTouchListener(TouchListener touchListener) {
        this.touchListener = touchListener;
    }

    interface TouchListener {
        void actionUp(int currentStarIndex);
    }

在主介面找到自定義view並且註冊監聽
2.記憶體優化 不要頻繁呼叫invalidate 必要時才呼叫
3.各種單位轉px：

    private float dp2px(int dp) {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, getResources().getDisplayMetrics());
    }

八 其他程式碼

佈局檔案

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.example.chj.customratingbar.CustomRatingBar
        android:id="@+id/customRatingBar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="10dp"
        app:normalStar="@drawable/star_normal"
        app:pressedStar="@drawable/star_pressed"
        app:starGap="20dp"
        app:starNumber="5" />

</RelativeLayout>

主介面

public class MainActivity extends AppCompatActivity implements CustomRatingBar.TouchListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        CustomRatingBar customRatingBar = findViewById(R.id.customRatingBar);
        customRatingBar.setTouchListener(this);
    }

    @Override
    public void actionUp(int currentStarIndex) {
        Toast.makeText(this, "按下了第" + (currentStarIndex + 1) + "個星星", Toast.LENGTH_SHORT).show();
    }
}

全程式碼
https://github.com/caihuijian/learn_darren_android.git