Android自定义ListView实现上拉加载与下拉刷新

本文将详细介绍如何在Android应用中通过自定义控件实现ListView的上拉加载更多和下拉刷新功能。我们将使用一个名为LoadLayout的自定义控件来处理上拉加载，并结合android.support.v4.widget.SwipeRefreshLayout来实现下拉刷新。

自定义控件LoadLayout

LoadLayout是一个自定义的FrameLayout，专门用于实现ListView的上拉加载功能。该控件通过监听ListView的滚动事件来判断用户是否已经滚动到列表底部，并在此基础上触发上拉加载的操作。

import android.content.Context;
import android.graphics.drawable.Animatable;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.widget.AbsListView;
import android.widget.FrameLayout;
import android.widget.ListView;
import android.widget.TextView;

import com.xh.boke.R;

public class LoadLayout extends FrameLayout implements AbsListView.OnScrollListener {

    private enum Operation {START, STOP}

    private int mTouchSlop;
    private ListView mListView;
    private TextView mFootText;
    private OnLoadListener mOnLoadListener;
    private View mListViewFooter;
    private int mYDown;
    private int mLastY;
    private boolean isLoading = false;

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

    public LoadLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
        mListViewFooter = LayoutInflater.from(context).inflate(R.layout.view_lv_footer, null, false);
        mFootText = (TextView) mListViewFooter.findViewById(R.id.pull_to_refresh_loadmore_text);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        if (mListView == null) {
            getListView();
        }
    }

    private void getListView() {
        int childs = getChildCount();
        if (childs > 0) {
            for (int i = 0; i                 View childView = getChildAt(i);
                if (childView instanceof ListView) {
                    mListView = (ListView) childView;
                    mListView.setOnScrollListener(this);
                }
            }
        }
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        final int action = event.getAction();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mYDown = (int) event.getRawY();
                break;
            case MotionEvent.ACTION_UP:
                mLastY = (int) event.getRawY();
                if (canLoad()) {
                    loadData();
                }
                break;
            default:
                break;
        }
        return super.dispatchTouchEvent(event);
    }

    private boolean canLoad() {
        return isBottom() && !isLoading && isPullUp();
    }

    private boolean isBottom() {
        if (mListView != null && mListView.getAdapter() != null) {
            return mListView.getLastVisiblePosition() == (mListView.getAdapter().getCount() - 1);
        }
        return false;
    }

    private boolean isPullUp() {
        return (mYDown - mLastY) >= mTouchSlop;
    }

    private void loadData() {
        if (mOnLoadListener != null) {
            setLoading(true);
            mOnLoadListener.onLoad();
        }
    }

    public void setLoading(boolean loading) {
        isLoading = loading;
        if (isLoading) {
            changeAnimation(Operation.START);
            mListView.addFooterView(mListViewFooter, null, false);
        } else {
            changeAnimation(Operation.STOP);
            mListView.removeFooterView(mListViewFooter);
            mYDown = 0;
            mLastY = 0;
        }
    }

    public void setOnLoadListener(OnLoadListener loadListener) {
        mOnLoadListener= loadListener;
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {}

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        if (canLoad()) {
            loadData();
        }
    }

    public static interface OnLoadListener {
        void onLoad();
    }

    private void changeAnimation(Operation operation) {
        Drawable[] drawables = mFootText.getCompoundDrawables();
        for (Drawable drawable : drawables) {
            if (drawable != null && drawable instanceof Animatable) {
                Animatable animatable = ((Animatable) drawable);
                switch (operation) {
                    case START:
                        animatable.start();
                        break;
                    case STOP:
                        animatable.stop();
                        break;
                }
            }
        }
    }
}

布局文件

为了使LoadLayout能够正常工作，我们需要定义两个XML布局文件：view_lv_footer.xml 和 rotating_loading.xml。

    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:background="#ffffff"
    android:gravity="center"
    android:paddingBottom="8dip"
    android:paddingTop="5dip">

            android:id="@+id/pull_to_refresh_loadmore_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:gravity="center"
        android:paddingTop="5dip"
        android:drawableLeft="@anim/rotating_loading"
        android:drawablePadding="8dp"
        android:text="加载中..."
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:textColor="@android:color/black"
        android:textSize="@dimen/activity_horizontal_margin"
        android:textStyle="bold" />

  xmlns:android="http://schemas.android.com/apk/res/android"
  android:pivotX="50%"
  android:pivotY="50%"
  android:drawable="@mipmap/ic_ref"
  android:duration="10" />

在Activity中使用

要在Activity中使用LoadLayout，首先需要在布局文件中引入LoadLayout，并设置其包含一个ListView。然后在Activity中找到LoadLayout实例，并为其设置上拉加载的监听器。

setContentView(R.layout.activity_main);
LoadLayout load = (LoadLayout) findViewById(R.id.load);
load.setOnLoadListener(this);

当数据加载完成后，可以通过调用setLoading(false)方法来关闭加载指示器。

load.setLoading(false);

主布局文件

最后，我们来看一下主布局文件activity_main.xml的定义：

    android:id="@+id/load"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

            android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />