Android自定义控件之仿汽车之家下拉刷新

关于下拉刷新的实现原理我在上篇文章Android自定义控件之仿美团下拉刷新中已经详细介绍过了，这篇文章主要介绍表盘的动画实现原理

汽车之家的下拉刷新分为三个状态：
第一个状态为下拉刷新状态(pull to refresh)，在这个状态下是一个表盘随着下拉的距离动态改变指针的角度
第二个状态为放开刷新状态(release to refresh)，在这个状态下是指针角度变化的一个动画

第一个状态的实现：

这个效果我们使用自定义View来实现，我们从汽车之家apk中拿到下拉刷新所用到的两张图片：


我们将第一张图片画在画布上作为背景，接着我们根据当前进度值来动态旋转画布，然后再将第二章图片画在画布上，我们看到表针的旋转实则是画布在旋转。

 @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
            //现将第一张图片画在画布上
            canvas.drawBitmap(finalBackGroundBitmap,0,0,null);
            //旋转画布
            canvas.rotate(mCurrentProgress*2.7f,x/2,y/2);
            //将第二张图片画在旋转后的画布上
            canvas.drawBitmap(finalPointerBitmap, 0, 0, null);
    }

自定义View的完整代码如下：

/**
 * Created by zhangqi on 15/10/17.
 */
public class AutoHome extends View{
    private Bitmap backGroundBitmap;
    public Bitmap pointerBitmap;
    private int x;
    private int y;
    private Bitmap finalBackGroundBitmap;
    private Bitmap finalPointerBitmap;
    private float mCurrentProgress;

    public AutoHome(Context context) {
        super(context);
        init(context);
    }


    public AutoHome(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

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


    private void init(Context context) {
        backGroundBitmap = Bitmap.createBitmap(BitmapFactory.decodeResource(context.getResources(), R.drawable.load_icon_dial2x));
        pointerBitmap = Bitmap.createBitmap(BitmapFactory.decodeResource(context.getResources(), R.drawable.load_icon_pointer2x));
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(measureWidth(widthMeasureSpec),measureWidth(heightMeasureSpec));
        x = getMeasuredWidth();
        y = getMeasuredHeight();
        finalBackGroundBitmap = Bitmap.createScaledBitmap(backGroundBitmap, x, y, false);
        finalPointerBitmap = Bitmap.createScaledBitmap(pointerBitmap, x, y, false);
    }
    private int measureWidth(int widMeasureSpec){
        int result = 0;
        int size = MeasureSpec.getSize(widMeasureSpec);
        int mode = MeasureSpec.getMode(widMeasureSpec);
        if (mode == MeasureSpec.EXACTLY){
            result = size;
        }else{
            result = backGroundBitmap.getWidth();
            if (mode == MeasureSpec.AT_MOST){
                result = Math.min(result,size);
            }
        }
        return result;

    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

            canvas.drawBitmap(finalBackGroundBitmap,0,0,null);
            canvas.rotate(mCurrentProgress*2.7f,x/2,y/2);
            canvas.drawBitmap(finalPointerBitmap, 0, 0, null);
    }


    public void setCurrentProgress(float progress){
        mCurrentProgress = progress*100;
    }
}

接着我们在Activity中用SeekBar来模拟一个进度值，从而传递给我们自定义View

public class MainActivity extends AppCompatActivity {
    private SeekBar mSeekBar;
    private AutoHome mAutoHome;
    private float mCurrentProgress;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mSeekBar = (SeekBar) findViewById(R.id.seekbar);
        mAutoHome = (AutoHome) findViewById(R.id.autohome);

        mSeekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
                mCurrentProgress = (float)seekBar.getProgress()/(float)seekBar.getMax();
                mAutoHome.setCurrentProgress(mCurrentProgress);
                mAutoHome.invalidate();
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        });
    }

第二个状态的实现：

第二个状态是表针在执行一个旋转的动画，我们可以将表针写成一个自定义View，然后表盘作为背景图片，然后表针View来执行rotate动画即可

/**
 * Created by zhangqi on 15/10/27.
 */
public class PointerView extends View {
    private int x;
    private int y;
    private Bitmap finalPointerBitmap;
    private Bitmap pointerBitmap;
    public PointerView(Context context) {
        super(context);
        init();
    }

    public PointerView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

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

    private void init() {
        pointerBitmap = Bitmap.createBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.load_icon_pointer2x));
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(measureWidth(widthMeasureSpec),measureWidth(heightMeasureSpec));
        x = getMeasuredWidth();
        y = getMeasuredHeight();
        finalPointerBitmap = Bitmap.createScaledBitmap(pointerBitmap, x, y, false);
    }
    private int measureWidth(int widMeasureSpec){
        int result = 0;
        int size = MeasureSpec.getSize(widMeasureSpec);
        int mode = MeasureSpec.getMode(widMeasureSpec);
        if (mode == MeasureSpec.EXACTLY){
            result = size;
        }else{
            result = pointerBitmap.getWidth();
            if (mode == MeasureSpec.AT_MOST){
                result = Math.min(result,size);
            }
        }
        return result;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //目的是让表针初始位置为270度！
        canvas.rotate(270,x/2,y/2);
        canvas.drawBitmap(finalPointerBitmap,0,0,null);
    }
}

然后我们在xml文件中这样写：

 <FrameLayout
    android:id="@+id/anim_container"
    android:layout_width="45dp"
    android:layout_height="45dp"
    android:layout_margin="15dp"
    android:visibility="gone" >

    <com.zhangqi.autohomerefreshlistview.PointerView
        android:id="@+id/anim_pointer"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center" />

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/load_icon_dial2x" />
    </FrameLayout>

这样就将表盘作为背景了，我们可以操作表针来执行rotate动画

<?xml version="1.0" encoding="utf-8"?>
<rotate xmlns:android="http://schemas.android.com/apk/res/android"
    android:fromDegrees="0"
    android:toDegrees="-150"
    android:pivotY="50%"
    android:pivotX="50%"
    android:duration="1000"
    android:repeatCount="infinite"
    android:repeatMode="reverse"

    >
</rotate>

mAutoHomeAnim = (PointerView) headerView.findViewById(R.id.anim_pointer);
animation = AnimationUtils.loadAnimation(context, R.anim.pointer_rotate);
//执行动画
mAutoHomeAnim.startAnimation(animation);

在listview中

由于下拉刷新核心代码和美团下拉刷新是一样的，这里我只截取不一样的部分

private void changeHeaderByState(int state){
        switch (state) {
        case DONE:
            headerView.setPadding(0, -headerViewHeight, 0, 0);
            //第一状态的view显示出来
            mAutoHome.setVisibility(View.VISIBLE);
            //先停止一下第二阶段view的动画
            mAutoHomeAnim.clearAnimation();
            //将第二阶段view隐藏起来
            mAnimContainer.setVisibility(View.GONE);
            break;
        case RELEASE_TO_REFRESH:
            tv_pull_to_refresh.setText("放开刷新");

            break;
        case PULL_TO_REFRESH:
            tv_pull_to_refresh.setText("下拉刷新");
            //第一状态view显示出来
            mAutoHome.setVisibility(View.VISIBLE);
            //停止第二阶段动画
            mAutoHomeAnim.clearAnimation();
            //将第二阶段view隐藏
            mAnimContainer.setVisibility(View.GONE);
            break;
        case REFRESHING:
            tv_pull_to_refresh.setText("正在刷新");
            //将第一阶段view隐藏
            mAutoHome.setVisibility(View.GONE);
            //将第二阶段view显示出来
            mAnimContainer.setVisibility(View.VISIBLE);
            //先停止第二阶段动画
            mAutoHomeAnim.clearAnimation();
            //启动第二阶段动画
            mAutoHomeAnim.startAnimation(animation);
            break;
        default:
            break;
        }
    }

完整代码：

大家可以到我的GitHub上下载