Android SwipeRefreshLayout详解

SwipeRefreshLayout是一个Google官方提供的下拉刷新控件，通过下拉刷新可以及时更新数据，提高用户体验。它主要有两个特点：

1. 支持多种样式的下拉刷新
2. 支持多种手势操作：下拉刷新、上拉加载更多、左滑、右滑

一、基本用法

1、首先在build.gradle中引入SwipeRefreshLayout库：

dependencies {
    implementation 'androidx.swiperefreshlayout:swiperefreshlayout:1.1.0'
}

2、在布局文件中添加SwipeRefreshLayout控件，注意SwipeRefreshLayout只能有一个子控件：

<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
    android:id="@+id/swipe_refresh_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    
    <RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
    
</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>

3、在Java代码中获取SwipeRefreshLayout控件，并设置刷新监听器：

SwipeRefreshLayout swipeRefreshLayout = findViewById(R.id.swipe_refresh_layout);
swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
    @Override
    public void onRefresh() {
        //下拉刷新操作
    }
});

4、在下拉刷新操作完成后，记得调用SwipeRefreshLayout的setRefreshing(false)方法，取消刷新状态：

swipeRefreshLayout.setRefreshing(false);

二、自定义样式

SwipeRefreshLayout提供了两种样式的刷新效果：传统样式和Material Design样式。我们可以通过setProgressBackgroundColorSchemeResource()和setColorSchemeResources()方法来改变刷新样式，也可以自定义实现更加炫酷的自己的刷新样式。

1、传统样式刷新：

swipeRefreshLayout.setProgressBackgroundColorSchemeResource(android.R.color.white);
swipeRefreshLayout.setColorSchemeResources(android.R.color.holo_blue_bright, 
    android.R.color.holo_green_light,
    android.R.color.holo_orange_light,
    android.R.color.holo_red_light);

2、Material Design样式刷新：

swipeRefreshLayout.setProgressBackgroundColorSchemeResource(android.R.color.white);
swipeRefreshLayout.setColorSchemeResources(R.color.colorAccent);

3、自定义样式刷新：

swipeRefreshLayout.setProgressBackgroundColorSchemeResource(R.color.colorPrimary);
swipeRefreshLayout.setColorSchemeResources(R.color.colorAccent);
swipeRefreshLayout.setProgressViewOffset(true, -100, 300);

//设置刷新视图
CustomRefreshView customRefreshView = new CustomRefreshView(context);
swipeRefreshLayout.addView(customRefreshView, ViewGroup.LayoutParams.MATCH_PARENT, 
    ViewGroup.LayoutParams.WRAP_CONTENT);

class CustomRefreshView extends View implements SwipeRefreshLayout.OnChildScrollUpCallback {
    Paint mPaint;
    int mOffsetTop = 0;

    public CustomRefreshView(Context context) {
        super(context);
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
        mPaint.setColor(Color.BLUE);
        mPaint.setStyle(Paint.Style.FILL);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawRect(0, 0 + mOffsetTop, getWidth(), getHeight() + mOffsetTop, mPaint);
    }

    //OnChildScrollUpCallback回调方法，返回值决定是否可以下拉刷新
    @Override
    public boolean canChildScrollUp(SwipeRefreshLayout parent, @Nullable View child) {
        return false;
    }

    public void setOffsetTop(int offsetTop) {
        mOffsetTop = offsetTop;
        invalidate();
    }
}

//刷新操作完成后调用，注意中间需要延时，确保CustomRefreshView滑动到顶部
ObjectAnimator animator = ObjectAnimator.ofInt(customRefreshView, "offsetTop", customRefreshView.mOffsetTop, 0);
animator.setDuration(300);
new Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
        swipeRefreshLayout.setRefreshing(false);
        animator.start();
    }
}, 1000);

三、手势操作

SwipeRefreshLayout除了支持下拉刷新外，还支持了上拉加载更多和左右滑动手势，我们可以通过setOnTouchListener()方法来监听触摸事件，并根据手势来进行逻辑处理。

1、上拉加载更多：

final LinearLayoutManager layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
recyclerView.setOnTouchListener(new OnSwipeTouchListener(this){
    @Override
    public void onBottom() {
        //上拉加载更多操作
    }
});

abstract class OnSwipeTouchListener implements OnTouchListener {
    private GestureDetector gestureDetector;

    public OnSwipeTouchListener(Context context) {
        gestureDetector = new GestureDetector(context, new GestureListener());
    }

    public void onLeftSwipe() {
    }

    public void onRightSwipe() {
    }

    public void onTop() {
    }

    public void onBottom() {
    }

    public boolean onTouch(View v, MotionEvent event) {
        return gestureDetector.onTouchEvent(event);
    }

    private final class GestureListener extends GestureDetector.SimpleOnGestureListener {
        private static final int SWIPE_THRESHOLD = 100;
        private static final int SWIPE_VELOCITY_THRESHOLD = 100;

        @Override
        public boolean onDown(MotionEvent e) {
            return true;
        }

        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            boolean result = false;
            try {
                float diffY = e2.getY() - e1.getY();
                float diffX = e2.getX() - e1.getX();
                if (Math.abs(diffX) > Math.abs(diffY)) {
                    if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                        if (diffX > 0) {
                            onRightSwipe();
                        } else {
                            onLeftSwipe();
                        }
                        result = true;
                    }
                } else {
                    if (Math.abs(diffY) > SWIPE_THRESHOLD && Math.abs(velocityY) > SWIPE_VELOCITY_THRESHOLD) {
                        if (diffY < 0) {
                            onTop();
                        } else {
                            onBottom();
                        }
                        result = true;
                    }
                }
            } catch (Exception exception) {
                exception.printStackTrace();
            }
            return result;
        }
    }
}

2、左右滑动：

recyclerView.setOnTouchListener(new OnSwipeTouchListener(this){
    @Override
    public void onLeftSwipe() {
        //左滑操作
    }

    @Override
    public void onRightSwipe() {
        //右滑操作
    }
});

四、小结

通过本文，我们详细了解了SwipeRefreshLayout的基本用法、颜色样式以及手势操作。SwipeRefreshLayout作为Android平台上常用的下拉刷新控件，具有良好的用户交互体验，对于提升应用质量具有重要意义。