[ApiDemos] ExpandableListActivity

简介

今天我们来看看 APIdemo中的 ExpandableListActivity，从名字来看，它是 Activity的子类，而且还与 Listview有关，Expandable是可张开的意思，那么他就是一个可张开的Listview。

特点

谷歌文档是这么说的：

ExpandableListActivity hosts a ExpandableListView object that can be bound to different data sources that provide a two-levels of data (the top-level is group, and below each group are children).

大概意思是 ExpandableListActivity持有 ExpandableListView对象，可以绑定不同的数据源来提供了两级的数据（第一级是组，每一组的下面是子组），也即是说它每个列表项有两个组，一个是主组，一个是它的子组。

如何使用

上面提到 ExpandableListActivity持有 ExpandableListView，要使用 ExpandableListView，就要为他提供一个 Adpter，这与Listview很类似，但也有不同，使用的是 BaseExpandableListAdapter, CursorTreeAdapter, ResourceCursorTreeAdapter, SimpleCursorTreeAdapter, SimpleExpandableListAdapter，谷歌文档给出的Demo就是使用BaseExpandableListAdapter，下面来看看源码。

public class ExpandableList1 extends ExpandableListActivity {

ExpandableListAdapter mAdapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Set up our adapter
    mAdapter = new MyExpandableListAdapter();
    setListAdapter(mAdapter);
    registerForContextMenu(getExpandableListView());
}

@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {
    menu.setHeaderTitle("Sample menu");
    menu.add(0, 0, 0, R.string.expandable_list_sample_action);
}

@Override
public boolean onContextItemSelected(MenuItem item) {
    ExpandableListContextMenuInfo info = (ExpandableListContextMenuInfo) item.getMenuInfo();

    String title = ((TextView) info.targetView).getText().toString();

    int type = ExpandableListView.getPackedPositionType(info.packedPosition);
    if (type == ExpandableListView.PACKED_POSITION_TYPE_CHILD) {
        int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition); 
        int childPos = ExpandableListView.getPackedPositionChild(info.packedPosition); 
        Toast.makeText(this, title + ": Child " + childPos + " clicked in group " + groupPos,
                Toast.LENGTH_SHORT).show();
        return true;
    } else if (type == ExpandableListView.PACKED_POSITION_TYPE_GROUP) {
        int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition); 
        Toast.makeText(this, title + ": Group " + groupPos + " clicked", Toast.LENGTH_SHORT).show();
        return true;
    }

    return false;
}


public class MyExpandableListAdapter extends BaseExpandableListAdapter {


    //该数组是为列表项中的主组提供数据。     
    private String[] groups = { "People Names", "Dog Names", "Cat Names", "Fish Names" };

    //这个数组是为展开后的项，也就是子组提供数据的，请注意他是一个二维数组
    private String[][] children = {
            { "Arnold", "Barry", "Chuck", "David" },
            { "Ace", "Bandit", "Cha-Cha", "Deuce" },
            { "Fluffy", "Snuggles" },
            { "Goldy", "Bubbles" }
    };

    public Object getChild(int groupPosition, int childPosition) {
        return children[groupPosition][childPosition];
    }

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

    public int getChildrenCount(int groupPosition) {
        return children[groupPosition].length;
    }

    //该方法是为ExpandableListView设置布局
    public TextView getGenericView() {
        // Layout parameters for the ExpandableListView
        AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT, 64);

        TextView textView = new TextView(ExpandableList1.this);
        textView.setLayoutParams(lp);
        // Center the text vertically
        textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);
        // Set the text starting position
        textView.setPadding(36, 0, 0, 0);
        return textView;
    }

    //该方法控制子组的显示，也就是列表项中点击了某一项后，展开的项。
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild,
            View convertView, ViewGroup parent) {
        TextView textView = getGenericView();
        textView.setText(getChild(groupPosition, childPosition).toString());
        return textView;
    }

    public Object getGroup(int groupPosition) {
        return groups[groupPosition];
    }

    public int getGroupCount() {
        return groups.length;
    }

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

    //该方法控制主组的显示，也就是列表项中首先显示的列表
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView,
            ViewGroup parent) {
        TextView textView = getGenericView();
        textView.setText(getGroup(groupPosition).toString());
        return textView;
    }

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

    public boolean hasStableIds() {
        return true;
    }

}
}

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public class ExpandableList1 extends ExpandableListActivity {

ExpandableListAdapter mAdapter;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

// Set up our adapter

mAdapter = new MyExpandableListAdapter();

setListAdapter(mAdapter);

registerForContextMenu(getExpandableListView());

}

@Override

public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {

menu.setHeaderTitle("Sample menu");

menu.add(0, 0, 0, R.string.expandable_list_sample_action);

}

@Override

public boolean onContextItemSelected(MenuItem item) {

ExpandableListContextMenuInfo info = (ExpandableListContextMenuInfo) item.getMenuInfo();

String title = ((TextView) info.targetView).getText().toString();

int type = ExpandableListView.getPackedPositionType(info.packedPosition);

if (type == ExpandableListView.PACKED_POSITION_TYPE_CHILD) {

int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition);

int childPos = ExpandableListView.getPackedPositionChild(info.packedPosition);

Toast.makeText(this, title + ": Child " + childPos + " clicked in group " + groupPos,

Toast.LENGTH_SHORT).show();

return true;

} else if (type == ExpandableListView.PACKED_POSITION_TYPE_GROUP) {

int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition);

Toast.makeText(this, title + ": Group " + groupPos + " clicked", Toast.LENGTH_SHORT).show();

return true;

}

return false;

}

public class MyExpandableListAdapter extends BaseExpandableListAdapter {

//该数组是为列表项中的主组提供数据。

private String[] groups = { "People Names", "Dog Names", "Cat Names", "Fish Names" };

//这个数组是为展开后的项，也就是子组提供数据的，请注意他是一个二维数组

private String[][] children = {

{ "Arnold", "Barry", "Chuck", "David" },

{ "Ace", "Bandit", "Cha-Cha", "Deuce" },

{ "Fluffy", "Snuggles" },

{ "Goldy", "Bubbles" }

};

public Object getChild(int groupPosition, int childPosition) {

return children[groupPosition][childPosition];

}

public long getChildId(int groupPosition, int childPosition) {

return childPosition;

}

public int getChildrenCount(int groupPosition) {

return children[groupPosition].length;

}

//该方法是为ExpandableListView设置布局

public TextView getGenericView() {

// Layout parameters for the ExpandableListView

AbsListView.LayoutParams lp = new AbsListView.LayoutParams(

ViewGroup.LayoutParams.MATCH_PARENT, 64);

TextView textView = new TextView(ExpandableList1.this);

textView.setLayoutParams(lp);

// Center the text vertically

textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);

// Set the text starting position

textView.setPadding(36, 0, 0, 0);

return textView;

}

//该方法控制子组的显示，也就是列表项中点击了某一项后，展开的项。

public View getChildView(int groupPosition, int childPosition, boolean isLastChild,

View convertView, ViewGroup parent) {

TextView textView = getGenericView();

textView.setText(getChild(groupPosition, childPosition).toString());

return textView;

}

public Object getGroup(int groupPosition) {

return groups[groupPosition];

}

public int getGroupCount() {

return groups.length;

}

public long getGroupId(int groupPosition) {

return groupPosition;

}

//该方法控制主组的显示，也就是列表项中首先显示的列表

public View getGroupView(int groupPosition, boolean isExpanded, View convertView,

ViewGroup parent) {

TextView textView = getGenericView();

textView.setText(getGroup(groupPosition).toString());

return textView;

}

public boolean isChildSelectable(int groupPosition, int childPosition) {

return true;

}

public boolean hasStableIds() {

return true;

}

从上面可以看到，BaseExpandableListAdapter其实是一个抽象类，使用时需要实现其中的方法，
比较主要的方法有 getGroupView(XXX)方法和 getChildView（XX），这两个方法分别控制主组的显示视图和子组的显示视图，返回值都是View对象。我们可以用 java代码来写布局，也可以通过布局填充的方式来加载（LayoutInflater ），Demo中是用的java代码。我个人觉得用 LayoutInflater比较方便。
在 BaseExpandableListAdapter需要定义两个数组，一个是为主组提供显示数据的一维数组，另一个是为展开项的子组提供数据的二位数组。

简介

特点

如何使用

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