Android实战简易教程-第五十三枪（通过实现OnScrollListener接口实现上拉加载更多功能）-CFANZ编程社区

支持上拉加载更多的控件有很多，但是你知道背后的原理吗？有一些面试官可能会问到这方便的知识，他们认为会用不是目的，懂背后的原理才是真人才。下面我们通过实现OnScrollListener接口实现上拉加载更多的效果，这里用到了回调接口，你需要对回调进行比较好的理解，回调机制是Android中很重要的机制，下面我们看一下代码：

1.定义一个footer.xml，用于下拉提示的效果：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <LinearLayout
        android:id="@+id/ll_footer"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical" >

        <ProgressBar
            android:id="@+id/progress"
            style="?android:attr/progressBarStyleSmall"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center" />

        <TextView
            android:id="@+id/tv_wait"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="正在加载..."
            android:textSize="10sp" />
    </LinearLayout>

</LinearLayout>

2.activity_main.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <com.example.listviewscrolldemo.LoadListView
        android:id="@+id/lv_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>

3.自定义LoadListView:

package com.example.listviewscrolldemo;

import android.content.Context;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ListView;

public class LoadListView extends ListView implements OnScrollListener {
  private int lastVisibleItem;// 最后一个可见项
  private int totalItems;// 所有项
  private View footer;// 底部布局
  private Boolean isLoading = false;
  private ILoadListener iListener;

  public LoadListView(Context context) {
    super(context);
    initView(context);
  }

  public LoadListView(Context context, AttributeSet attrs) {
    super(context, attrs);
    initView(context);
  }

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

  /**
   * 添加底部加载提示到布局Listview
   * 
   * @param context
   */
  private void initView(Context context) {
    LayoutInflater inflater = LayoutInflater.from(context);
    footer = inflater.inflate(R.layout.footer, null);
    footer.findViewById(R.id.ll_footer).setVisibility(View.GONE);// 首先设置加载提示不可见
    this.addFooterView(footer);
    this.setOnScrollListener(this);// 设置滚动监听

  }

  @Override
  public void onScrollStateChanged(AbsListView view, int scrollState) {
    if (lastVisibleItem == totalItems && scrollState == SCROLL_STATE_IDLE) {

      if (!isLoading) {// 判断不是正在加载！
        footer.findViewById(R.id.ll_footer).setVisibility(View.VISIBLE);// 首先设置加载提示可见
        iListener.onLoad();
        isLoading = true;
      }

    }

  }

  @Override
  public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
    this.lastVisibleItem = firstVisibleItem + visibleItemCount;
    this.totalItems = totalItemCount;
  }

  // 传递
  public void setInterface(ILoadListener iListener) {
    this.iListener = iListener;
  }

  /**
   * 加载更多数据的回调接口
   * 
   * @author Administrator
   *
   */
  public interface ILoadListener {
    public void onLoad();
  }

  // 加载完毕
  public void loadCompleted() {
    isLoading = false;
    footer.findViewById(R.id.ll_footer).setVisibility(View.GONE);
  }

}

4.MainActivity.java:

package com.example.listviewscrolldemo;

import java.util.ArrayList;
import java.util.List;

import com.example.listviewscrolldemo.LoadListView.ILoadListener;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.widget.ArrayAdapter;

public class MainActivity extends Activity implements ILoadListener {
  private LoadListView mListView;
  private ArrayAdapter<String> adapter;
  private List<String> datas;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initViews();
    initDatas();
  }

  private void initDatas() {
    for (int i = 1; i < 21; i++) {
      datas.add("数据" + i + "");
    }

  }

  private void initMoreDatas() {
    for (int i = 1; i < 3; i++) {
      datas.add("新数据" + i + "");
    }

  }

  private void initViews() {
    mListView = (LoadListView) findViewById(R.id.lv_main);
    mListView.setInterface(this);
    datas = new ArrayList<String>();
    adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, datas);
    // adapter=new
    // ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_list_item_1);
    mListView.setAdapter(adapter);
  }

  @Override
  public void onLoad() {
    // 添加延时效果
    Handler handler = new Handler();
    handler.postDelayed(new Runnable() {
      public void run() {

        initMoreDatas();// 获取更多数据
        adapter.notifyDataSetChanged();// 刷新ListView
        mListView.loadCompleted();// 隐藏加载提示
      }
    }, 2000);

  }
}