自定义view之继承控件

前面两篇文章已经把组合控件和自绘控件介绍了，咱们这一次就来看看继承控件的关键点！

继承控件就是继承已有的控件，创建新控件，保留继承的父控件的特性，并且还可以引入新特性。下面就以支持横向滑动删除列表项的自定义ListView的实现来介绍。

1、创建删除按钮布局delete_btn.xml，这个布局是在横向滑动列表项后显示的页面效果：

<?xml version="1.0" encoding="utf-8"?><Button xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:background="#ff00"    android:padding="5px"    android:text="删除"    android:textColor="#f7f5f5"    android:textSize="16px"    android:textStyle="bold"></Button>

2、创建CustomListView类，继承自ListView，并实现了OnTouchListener和OnGestureListener接口：

public class CustomListView extends ListView implements View.OnTouchListener,        GestureDetector.OnGestureListener {    //手势动作探测器    private GestureDetector mGestureDetector;    // 删除事件监听器    public interface OnDeleteListener {        void onDelete(int index);    }    private OnDeleteListener mOnDeleteListener;    //删除的按钮    private View mDeleteBtn;    //列表项布局    private ViewGroup mItemLayout;    // 选择的列表项    private int mSelectedItem;    // 当前删除按钮是否显示出来了    private boolean isDeleteShown;    public CustomListView(Context context, AttributeSet attrs) {        super(context, attrs);        initialization();    }    //初始化操作    private void initialization() {        //创建手势监听器对象        mGestureDetector = new GestureDetector(getContext(), this);        //监听onTouch事件        setOnTouchListener(this);    }    // 设置删除监听事件    public void setOnDeleteListener(OnDeleteListener listener) {        mOnDeleteListener = listener;    }    @Override    public boolean onDown(MotionEvent e) {        if (!isDeleteShown) {            mSelectedItem = pointToPosition((int) e.getX(), (int) e.getY());        }        return false;    }    @Override    public void onShowPress(MotionEvent e) {    }    @Override    public boolean onSingleTapUp(MotionEvent e) {        return false;    }    @Override    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {        return false;    }    @Override    public void onLongPress(MotionEvent e) {    }    @Override    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {        // 如果当前删除按钮没有显示出来，并且x方向滑动的速度大于y方向的滑动速度        if (!isDeleteShown && Math.abs(velocityX) > Math.abs(velocityY)) {            mDeleteBtn = LayoutInflater.from(getContext()).inflate(                    R.layout.delete_btn, null);            mDeleteBtn.setOnClickListener(new OnClickListener() {                @Override                public void onClick(View v) {                    mItemLayout.removeView(mDeleteBtn);                    mDeleteBtn = null;                    isDeleteShown = false;                    mOnDeleteListener.onDelete(mSelectedItem);                }            });            mItemLayout = (ViewGroup) getChildAt(mSelectedItem                    - getFirstVisiblePosition());            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(                    LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);            params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);            params.addRule(RelativeLayout.CENTER_VERTICAL);            mItemLayout.addView(mDeleteBtn, params);            isDeleteShown = true;        }        return false;    }    //触摸删除监听事件    @Override    public boolean onTouch(View v, MotionEvent event) {        if (isDeleteShown) {            hideDelete();            return false;        } else {            return mGestureDetector.onTouchEvent(event);        }    }    // 隐藏删除按钮    public void hideDelete() {        mItemLayout.removeView(mDeleteBtn);        mDeleteBtn = null;        isDeleteShown = false;    }    public boolean isDeleteShown() {        return isDeleteShown;    }}

3、定义列表项布局custom_listview_item.xml，它的结构很简单，只包含了一个TextView：

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical">    <TextView        android:id="@+id/content_tv"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_centerVertical="true"        android:layout_margin="30px"        android:gravity="center_vertical|left" /></RelativeLayout>

4、定义适配器类CustomListViewAdapter，继承自ArrayAdapter<String>：

package com.example.administrator.myapplication;import android.content.Context;import android.support.annotation.NonNull;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ArrayAdapter;import android.widget.TextView;import java.util.List;/** * Created by Administrator on 2017/1/4 0004. */public class CustomListViewAdapter extends ArrayAdapter<String> {    public CustomListViewAdapter(Context context, int resource, List<String> objects) {        super(context, resource, objects);    }    @NonNull    @Override    public View getView(int position, View convertView, ViewGroup parent) {        View view;        if (convertView == null) {            view = LayoutInflater.from(getContext()).inflate(                    R.layout.custom_listview_item, null);        } else {            view = convertView;        }        TextView contentTv = (TextView) view.findViewById(R.id.content_tv);        contentTv.setText(getItem(position));        return view;    }}

5、在activity_main.xml中引入自定义的ListView：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:id="@+id/activity_main"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.example.administrator.myapplication.MainActivity">    <com.example.administrator.myapplication.CustomListView            android:id="@+id/custom_lv"            android:layout_width="match_parent"             android:layout_height="wrap_content" /></LinearLayout>

6、在MainActivity中对列表做初始化、设置列表项删除按钮点击事件等处理：

package com.example.administrator.myapplication;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Toast;import java.util.ArrayList;import java.util.List;/*    Android自定义View的三种实现方式*       1、组合控件*       2、自绘控件*       3、继承控件**** */public class MainActivity extends AppCompatActivity {    // 自定义Lv    private CustomListView mCustomLv;    // 自定义适配器    private CustomListViewAdapter mAdapter;    // 内容列表    private List<String> contentList = new ArrayList<String>();    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initContentList();        initview();    }    private void initContentList() {        for (int i = 0; i < 20; i++) {            contentList.add("内容项" + i);        }    }    private void initview() {        mCustomLv = (CustomListView) findViewById(R.id.custom_lv);        mCustomLv.setOnDeleteListener(new CustomListView.OnDeleteListener() {            @Override            public void onDelete(int index) {                contentList.remove(index);                mAdapter.notifyDataSetChanged();            }        });        mAdapter = new CustomListViewAdapter(MainActivity.this, 0, contentList);        mCustomLv.setAdapter(mAdapter);    }    @Override    public void onBackPressed() {        if (mCustomLv.isDeleteShown()) {            mCustomLv.hideDelete();            return;        }        super.onBackPressed();    }}

7、运行效果如下：