話不多少亥贸，先上效果圖過(guò)一下癮。

演示動(dòng)畫(huà)

經(jīng)我網(wǎng)上一搜捞高，沒(méi)有很好的實(shí)例來(lái)單獨(dú)實(shí)現(xiàn)以上效果氯材，所以只能老司機(jī)自己出馬了。為了實(shí)現(xiàn)以上效果硝岗，當(dāng)然離不開(kāi)我們對(duì)onTouchEvent事件的處理了氢哮，老司機(jī)們應(yīng)該都懂的，開(kāi)始開(kāi)車型檀，嘟嘟~

開(kāi)車

下面來(lái)說(shuō)一下思路冗尤，首先上一張圖，讓我更方便地來(lái)為乘客們講解胀溺。

旋轉(zhuǎn)解析圖

好了裂七，重要的都已經(jīng)在圖中說(shuō)了，下面只需要一個(gè)回調(diào)便可在外部獲取到旋轉(zhuǎn)的角度仓坞，獻(xiàn)上相關(guān)重要代碼背零，相信根據(jù)我的注釋，大家也都應(yīng)該明白了无埃。

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.ImageView;

/**
 * <pre>
 *     author: Blankj
 *     blog  : http://blankj.com
 *     time  : 2016/11/8
 *     desc  :
 * </pre>
 */
public class RotateImageView extends ImageView {

    // 點(diǎn)擊在view中所在坐標(biāo)
    private float x, y;
    // view的中心點(diǎn)坐標(biāo)
    private float ox, oy;
    // view的寬徙瓶、高
    private int w, h;
    private Matrix matrix;
    // ImageView的資源圖片
    Bitmap mBitmap;
    // 旋轉(zhuǎn)過(guò)的角度
    public  float   totalDegree = 0;
    // 是否初始化過(guò)
    private boolean isInit      = false;

    // 旋轉(zhuǎn)角度改變的監(jiān)聽(tīng)器
    private OnRotationChangeListener mListener;

    public void setOnRotationChangeListener(OnRotationChangeListener listener) {
        mListener = listener;
    }

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

    public RotateImageView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

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

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        // 已初始化完畢的話那就直接滾回老家去吧
        if (isInit) return;
        int measureWidth = getWidth();
        int measureHeight = getHeight();
        Log.d("blankj", "onMeasure: w: " + measureWidth + ", h: " + measureHeight);
        // 如果沒(méi)有初始化過(guò)，就初始化
        if (measureWidth != 0 && measureHeight != 0 && !isInit) {
            isInit = true;
            mBitmap = ((BitmapDrawable) this.getDrawable()).getBitmap();
            w = measureWidth;
            h = measureHeight;
            ox = w >> 1;
            oy = h >> 1;
            matrix = new Matrix();
            // 獲取適配于ImageView的bitmap
            mBitmap = Bitmap.createScaledBitmap(mBitmap, w, h, true);
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        Log.d("blankj", "onDraw");
        // 判空以防崩潰
        if (mBitmap == null) return;
        canvas.save();
        canvas.drawBitmap(mBitmap, matrix, null);
        canvas.restore();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                x = event.getX();
                y = event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                float nowX = event.getX();
                float nowY = event.getY();

                // 計(jì)算三邊的平方
                float ab2 = (x - nowX) * (x - nowX) + (y - nowY) * (y - nowY);
                float oa2 = (x - ox) * (x - ox) + (y - oy) * (y - oy);
                float ob2 = (nowX - ox) * (nowX - ox) + (nowY - oy) * (nowY - oy);

                // 根據(jù)兩向量的叉乘來(lái)判斷順逆時(shí)針
                boolean isClockwise = ((x - ox) * (nowY - oy) - (y - oy) * (nowX - ox)) > 0;

                // 根據(jù)余弦定理計(jì)算旋轉(zhuǎn)角的余弦值
                double cosDegree = (oa2 + ob2 - ab2) / (2 * Math.sqrt(oa2) * Math.sqrt(ob2));

                // 異常處理录语，因?yàn)樗愠鰜?lái)會(huì)有誤差絕對(duì)值可能會(huì)超過(guò)一倍啥，所以需要處理一下
                if (cosDegree > 1) {
                    cosDegree = 1;
                } else if (cosDegree < -1) {
                    cosDegree = -1;
                }

                // 計(jì)算弧度
                double radian = Math.acos(cosDegree);

                // 計(jì)算旋轉(zhuǎn)過(guò)的角度禾乘，順時(shí)針為正澎埠，逆時(shí)針為負(fù)
                float degree = (float) (isClockwise ? Math.toDegrees(radian) : -Math.toDegrees(radian));

                // 累加角度
                totalDegree += degree;
                matrix.setRotate(totalDegree, ox, oy);

                // 更新觸摸點(diǎn)
                x = nowX;
                y = nowY;

                // 回調(diào)把角度拋出
                if (mListener != null) {
                    mListener.getRotation((int) totalDegree);
                }

                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                // 如果圖片需要復(fù)原原來(lái)角度，調(diào)用下方代碼
//                matrix.setRotate(totalDegree, ox, oy);
//                invalidate();
                break;
        }
        return true;
    }

    public void reset() {
        totalDegree = 0;
        matrix.setRotate(totalDegree, ox, oy);
        invalidate();
    }

    public interface OnRotationChangeListener {
        void getRotation(int degree);
    }
}

好了始藕，乘客們蒲稳，終點(diǎn)站已到，謝謝你們旅途中的陪伴伍派，老司機(jī)馬上要下班了江耀，啊哈哈哈，還是那句話：“你不買東西也是沒(méi)錢诉植，買了東西也是沒(méi)錢祥国，那就說(shuō)明買東西它不要錢啊”，祝大家雙十一購(gòu)物愉快晾腔。

最后獻(xiàn)上源碼地址：GetRotateDegree舌稀，歡迎大家star和fork。