Android自定义组件系列【5】——进阶实践（2）

上一篇《Android自定义组件系列【5】——进阶实践（1）》中对任老师的《可下拉的PinnedHeaderExpandableListView的实现》前一部分进行了实现，这一篇我们来看看ExpandableListView的使用并实现剩下的部分。

原文出处：http://blog.csdn.net/singwhatiwanna/article/details/25546871

一、ExpandableListView的用法

ExpandableListView是ListView的子类，它在普通ListView的基础上进行了扩展，适配器为ExpandableListAdapter。



与Adapter类似的是，实现ExpandableListAdapter也有如下方式：

1、扩展BaseExpandableListAdapter实现ExpandableListAdapter

2、使用SimpleExpandableListAdapter将两个List集合包装成ExpandableListAdapter

3、使用SimpleCursorTreeAdapter将Cursor中的数据包装成SimpleCursorTreeAdapter

接下来用第一种方式来做个小例子，来看看ExpandableListView的使用

ExpandableListAdapter adapter = new BaseExpandableListAdapter() {

@Override
public boolean isChildSelectable(int arg0, int arg1) {
// TODO Auto-generated method stub
return false;
}

@Override
public boolean hasStableIds() {
// TODO Auto-generated method stub
return false;
}

@Override
public View getGroupView(int arg0, boolean arg1, View arg2, ViewGroup arg3) {
// TODO Auto-generated method stub
return null;
}

@Override
public long getGroupId(int arg0) {
// TODO Auto-generated method stub
return 0;
}

@Override
public int getGroupCount() {
// TODO Auto-generated method stub
return 0;
}

@Override
public Object getGroup(int arg0) {
// TODO Auto-generated method stub
return null;
}

@Override
public int getChildrenCount(int arg0) {
// TODO Auto-generated method stub
return 0;
}

@Override
public View getChildView(int arg0, int arg1, boolean arg2, View arg3,
ViewGroup arg4) {
// TODO Auto-generated method stub
return null;
}

@Override
public long getChildId(int arg0, int arg1) {
// TODO Auto-generated method stub
return 0;
}

@Override
public Object getChild(int arg0, int arg1) {
// TODO Auto-generated method stub
return null;
}
};

可以看到BaseExpandableListApdater中的方法很多，主要方法介绍如下：

getGroupCount():返回组列表数量

getGroupView():返回的View作为组列表项

getChildrenCount():返回子列表项的数量

getChildView():返回的View作为特定组、特定位置的子列表项

package com.example.expandablelistviewtest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.BaseExpandableListAdapter;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ExpandableListAdapter adapter = new BaseExpandableListAdapter() {

int[] logos = new int[] {
R.drawable.ic_launcher,
R.drawable.ic_launcher,
R.drawable.ic_launcher
};

private String[] groupTypes = new String[]{
"计算机语言", "人类语言", "动物语言"
};

private String[][] childTypes = new String[][] {
{"Java", "C++", "C", "PHP"},
{"汉语", "英语", "日语", "法语"},
{"咕咕", "汪汪", "喵喵"}
};

// 获取指定组位置、指定子列表项处的子列表项数据
@Override
public Object getChild(int groupPosition, int childPosition) {
return childTypes[groupPosition][childPosition];
}

@Override
public long getChildId(int groupPosition, int childPosition) {
return childPosition;
}

@Override
public int getChildrenCount(int groupPosition) {
return childTypes[groupPosition].length;
}

private TextView getTextView() {
AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
ViewGroup.LayoutParams.MATCH_PARENT, 64);
TextView textView = new TextView(MainActivity.this);
textView.setLayoutParams(lp);
textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);
textView.setPadding(36, 0, 0, 0);
textView.setTextSize(20);
return textView;
}

// 该方法决定每个子选项的外观
@Override
public View getChildView(int groupPosition, int childPosition,
boolean isLastChild, View convertView, ViewGroup parent) {
TextView textView = getTextView();
textView.setText(getChild(groupPosition, childPosition)
.toString());
return textView;
}

// 获取指定组位置处的组数据
@Override
public Object getGroup(int groupPosition) {
return groupTypes[groupPosition];
}

@Override
public int getGroupCount() {
return groupTypes.length;
}

@Override
public long getGroupId(int groupPosition) {
return groupPosition;
}

// 该方法决定每个组选项的外观
@Override
public View getGroupView(int groupPosition, boolean isExpanded,
View convertView, ViewGroup parent) {
LinearLayout ll = new LinearLayout(MainActivity.this);
ll.setOrientation(0);
ImageView logo = new ImageView(MainActivity.this);
logo.setImageResource(logos[groupPosition]);
ll.addView(logo);
TextView textView = getTextView();
textView.setText(getGroup(groupPosition).toString());
ll.addView(textView);
return ll;
}

@Override
public boolean isChildSelectable(int groupPosition,
int childPosition) {
return true;
}

@Override
public boolean hasStableIds() {
return true;
}
};
ExpandableListView expandListView = (ExpandableListView) findViewById(R.id.list);
expandListView.setAdapter(adapter);
}

}

<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<ExpandableListView
android:id="@+id/list"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>

</RelativeLayout>

二、代码分析

首先看onCreate方法：

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
expandableListView = (PinnedHeaderExpandableListView) findViewById(R.id.expandablelist);
stickyLayout = (StickyLayout)findViewById(R.id.sticky_layout);
initData();

adapter = new MyexpandableListAdapter(this);
expandableListView.setAdapter(adapter);

// 展开所有group
for (int i = 0, count = expandableListView.getCount(); i < count; i++) {
expandableListView.expandGroup(i);
}

expandableListView.setOnHeaderUpdateListener(this);
expandableListView.setOnChildClickListener(this);
expandableListView.setOnGroupClickListener(this);
stickyLayout.setOnGiveUpTouchEventListener(this);

}

前面几行很容易，和上面的例子几乎一样，我们只需要再关注一下initData()方法和下面的几行监听函数。

initData()中是模拟的数据，如下：

void initData() {
groupList = new ArrayList<Group>();
Group group = null;
for (int i = 0; i < 3; i++) {
group = new Group();
group.setTitle("group-" + i);
groupList.add(group);
}

childList = new ArrayList<List<People>>();
for (int i = 0; i < groupList.size(); i++) {
ArrayList<People> childTemp;
if (i == 0) {
childTemp = new ArrayList<People>();
for (int j = 0; j < 13; j++) {
People people = new People();
people.setName("yy-" + j);
people.setAge(30);
people.setAddress("sh-" + j);

childTemp.add(people);
}
} else if (i == 1) {
childTemp = new ArrayList<People>();
for (int j = 0; j < 8; j++) {
People people = new People();
people.setName("ff-" + j);
people.setAge(40);
people.setAddress("sh-" + j);

childTemp.add(people);
}
} else {
childTemp = new ArrayList<People>();
for (int j = 0; j < 23; j++) {
People people = new People();
people.setName("hh-" + j);
people.setAge(20);
people.setAddress("sh-" + j);

childTemp.add(people);
}
}
childList.add(childTemp);
}

}

接下来我们看看监听这几个监听函数

public class MainActivity extends Activity implements
ExpandableListView.OnChildClickListener,
ExpandableListView.OnGroupClickListener,
OnHeaderUpdateListener, OnGiveUpTouchEventListener {

从Activity的继承关系上看，OnChildClickListener和OnGroupClickListener是ExpandableListView类的监听函数。

@Override
public boolean onGroupClick(final ExpandableListView parent, final View v,
int groupPosition, final long id) {

return false;
}

@Override
public boolean onChildClick(ExpandableListView parent, View v,
int groupPosition, int childPosition, long id) {
Toast.makeText(MainActivity.this,
childList.get(groupPosition).get(childPosition).getName(), 1)
.show();

return false;
}

再来看看OnHeaderUpdateListener，这个监听函数实际上是在重写（自定义）的ExpandableListView中自定义的监听。

public void setOnHeaderUpdateListener(OnHeaderUpdateListener listener) {
mHeaderUpdateListener = listener;
if (listener == null) {
return;
}
mHeaderView = listener.getPinnedHeader();
int firstVisiblePos = getFirstVisiblePosition();
int firstVisibleGroupPos = getPackedPositionGroup(getExpandableListPosition(firstVisiblePos));
listener.updatePinnedHeader(firstVisibleGroupPos);
requestLayout();
postInvalidate();
}

getPinnedHeader()方法创建（得到）一个列表头，然后通过updatePinnedHeader方法设置当前可见的子列表元素的组名称。

requestLayout()方法的作用是当view确定自身已经不再适合现有的区域时，该view本身调用这个方法要求parent view重新调用他的onMeasure onLayout来对重新设置自己位置。特别的当view的layoutparameter发生改变，并且它的值还没能应用到view上，这时候适合调用这个方法。

postInvalidate()方法的作用是实现界面刷新。

public interface OnHeaderUpdateListener {
/**
* 采用单例模式返回同一个view对象即可
* 注意：view必须要有LayoutParams
*/
public View getPinnedHeader();

public void updatePinnedHeader(int firstVisibleGroupPos);
}

从OnHeaderUpdateListener监听函数的定义上看，当触发监听后会调用两个方法的实现如下：

@Override
public View getPinnedHeader() {
if (mHeaderView == null) {
mHeaderView = (ViewGroup) getLayoutInflater().inflate(R.layout.group, null);
mHeaderView.setLayoutParams(new LayoutParams(
LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
}
return mHeaderView;
}

@Override
public void updatePinnedHeader(int firstVisibleGroupPos) {
Group firstVisibleGroup = (Group) adapter.getGroup(firstVisibleGroupPos);
TextView textView = (TextView) getPinnedHeader().findViewById(R.id.group);
textView.setText(firstVisibleGroup.getTitle());
}

接下来我们需要知道什么情况下回触发这个监听函数。

protected void refreshHeader() {
if (mHeaderView == null) {
return;
}
int firstVisiblePos = getFirstVisiblePosition();
int pos = firstVisiblePos + 1;
int firstVisibleGroupPos = getPackedPositionGroup(getExpandableListPosition(firstVisiblePos));
int group = getPackedPositionGroup(getExpandableListPosition(pos));

if (group == firstVisibleGroupPos + 1) {
View view = getChildAt(1);
if (view.getTop() <= mHeaderHeight) {
int delta = mHeaderHeight - view.getTop();
mHeaderView.layout(0, -delta, mHeaderWidth, mHeaderHeight - delta);
}
} else {
mHeaderView.layout(0, 0, mHeaderWidth, mHeaderHeight);
}

if (mHeaderUpdateListener != null) {
mHeaderUpdateListener.updatePinnedHeader(firstVisibleGroupPos);
}
}

可以看到再调用refreshHeader()方法的时候会触发updatePinnerHeader方法。

@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if (totalItemCount > 0) {
refreshHeader();
}
if (mScrollListener != null) {
mScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
}
}

呵呵，这下终于恍然大悟了，在onScroll方法中调用了refreshHeader，这就是说在滑动屏幕的时候OnHeaderUpdateListener监听会触发，会不断的判断是否应该改变列名称。

快凌晨1点钟了，今天就分析到这吧，明天继续。

再次声明一下，本文是为了学习Android自定义组件，对任老师博客《可下拉的PinnedHeaderExpandableListView的实现》进行详细解读，如果有问题希望指出。

原文出处：http://blog.csdn.net/singwhatiwanna/article/details/25546871