//MyCircleView類public class MyCircleView extends View{ //當前畫筆畫圓的顏色 private int CurrenCircleBoundColor; private Paint paint; ////從xml中獲取的顏色 private int circleBundColor; private float circleBoundWidth; private float pivotX; private float pivotY; private float radius=130; private float currentDegree=0; private int currentSpeed=1; private boolean isPause=false; public MyCircleView(Context context) {  super(context);  initView(context); } public MyCircleView(Context context, @Nullable AttributeSet attrs) {  super(context, attrs);  initView(context);  TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.MyCircleView);  for (int i = 0; i < typedArray.getIndexCount(); i++) {   //就是我們自定義的屬性的資源id   int attr = typedArray.getIndex(i);   switch (attr){    case R.styleable.MyCircleView_circlr_bound_color:     circleBundColor = typedArray.getColor(attr, Color.RED);     CurrenCircleBoundColor=circleBundColor;     break;    case R.styleable.MyCircleView_circlr_bound_width:     circleBoundWidth = typedArray.getDimension(attr, 3);     break;   }  } } public MyCircleView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {  super(context, attrs, defStyleAttr);  initView(context); } private void initView(Context context){  paint = new Paint(); } public void setColor(int color){  if (CurrenCircleBoundColor!=color){   CurrenCircleBoundColor=color;  }else {   CurrenCircleBoundColor=circleBundColor;  } } @Override protected void onDraw(Canvas canvas) {  super.onDraw(canvas);  paint.setAntiAlias(true);  paint.setColor(CurrenCircleBoundColor);  paint.setStrokeWidth(circleBoundWidth);  paint.setStyle(Paint.Style.STROKE);  pivotX = getWidth() / 2;  pivotY = getHeight() / 2;  canvas.drawCircle(pivotX,pivotY,radius,paint);  canvas.save();  //旋轉畫布 , 如果旋轉的的度數大的話,視覺上看著是旋轉快的  canvas.rotate(currentDegree,pivotX,pivotY);  //提供了一些api可以用來畫線(畫路徑)  Path path = new Path();  //從哪開始畫 從A開始畫  path.moveTo(pivotX+radius,pivotY);  //從A點畫一個直線到D點  path.lineTo(pivotX+radius-20,pivotY-20);  //從D點畫一個直線到B點  path.lineTo(pivotX+radius,pivotY+20);  //從B點畫一個直線到C點  path.lineTo(pivotX+radius+20,pivotY-20);  //閉合 -- 從C點畫一個直線到A點  path.close();  paint.setStyle(Paint.Style.FILL);  paint.setColor(Color.BLACK);  canvas.drawPath(path,paint);  canvas.restore();  //旋轉的度數一個一個度數增加, 如果乘以一個速度的話,按一個速度速度增加  currentDegree+=1*currentSpeed;  if (!isPause){   invalidate();  } } public void speed(){  ++currentSpeed;  if (currentSpeed>=10){   currentSpeed=10;   Toast.makeText(getContext(),"我比閃電還快",Toast.LENGTH_SHORT).show();  } } public void slowDown(){  --currentSpeed;  if (currentSpeed<=1){   currentSpeed=1;  } } public void pauseOrStart(){  //如果是開始狀態的話去重新繪制  if (isPause){   isPause=!isPause;   invalidate();  }else {   isPause=!isPause;  } }}//主頁面public class MainActivity extends AppCompatActivity { //全局變量 private MyCircleView my_view; @Override protected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.activity_main);  //找控件  my_view = (MyCircleView) findViewById(R.id.my_view); } public void onClick(View view){  my_view.setColor(Color.BLUE); } public void add(View view){  my_view.speed(); } public void slow(View view){  my_view.slowDown(); } public void pauseOrStart(View view){  my_view.pauseOrStart(); }}主頁面布局<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.example.lx_20170928.MainActivity"> <Button  android:id="@+id/set_color_btn"  android:layout_width="match_parent"  android:layout_height="wrap_content"  android:layout_centerHorizontal="true"  android:onClick="onClick"  android:text="設置顏色" /> <Button  android:id="@+id/add"  android:layout_width="match_parent"  android:layout_height="wrap_content"  android:layout_below="@id/set_color_btn"  android:layout_centerHorizontal="true"  android:onClick="add"  android:text="加速" /> <Button  android:id="@+id/slow"  android:layout_width="match_parent"  android:layout_height="wrap_content"  android:layout_below="@+id/add"  android:layout_centerHorizontal="true"  android:onClick="slow"  android:text="減速" /> <Button  android:id="@+id/pause_or_start"  android:layout_width="match_parent"  android:layout_height="wrap_content"  android:layout_below="@+id/slow"  android:layout_centerHorizontal="true"  android:onClick="pauseOrStart"  android:text="暫定/開始" />  <com.example.lx_20170928.MyCircleView   android:layout_width="wrap_content"   android:layout_height="wrap_content"   android:id="@+id/my_view"   android:layout_centerInParent="true"   app:circlr_bound_color="@color/colorAccent"   app:circlr_bound_width="3dp"   /></RelativeLayout>//在values建一個attrs.xml<resources> <declare-styleable name="MyCustomCircleArrowView">  <attr name="circlr_bound_width" format="dimension"></attr>  <attr name="circlr_bound_color" format="color"></attr> </declare-styleable></resources>