Android基础——ListView

ListView是什么？

ListView以列表的形式展现数据，用户可通过对屏幕的上下滑动加载数据。

纯列表ListView——默认适配布局

在activity_main.xml中加入ListView：

修改MainActivity，用系统自带的ArrayAdapter，参数分别为Context、适配布局id和要适配的数据，这里适配布局采用内置布局android.R.layout.simple_list_item_1

public class MainActivity extends AppCompatActivity {

    private String[] data = {"A", "B", "C", "D", "E", "F", "G", "H"};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ArrayAdapter adapter = new ArrayAdapter<>(MainActivity.this, android.R.layout.simple_list_item_1, data);
        ListView listView = findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }
}

效果图：

适配ListView

适配数据

准备数据，创建名为Data的bean类

public class Data {
    private String name;
    private int imageId;

    public Data(String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getImageId() {
        return imageId;
    }

    public void setImageId(int imageId) {
        this.imageId = imageId;
    }
}

适配布局

准备ListView的适配布局，创建list_item.xml：

ArrayAdapter

创建数据适配器，重写构造器暂存数据、重写getView()方法加载布局并获取控件设置数据

public class DataAdapter extends ArrayAdapter {

    private int resourceId;

    public DataAdapter(@NonNull Context context, int resource, @NonNull List objects) {
        super(context, resource, objects);
        resourceId = resource;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        Data data = getItem(position);
        View view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
        ImageView dataIv = view.findViewById(R.id.list_iv);
        TextView dataTv = view.findViewById(R.id.list_tv);
        dataIv.setImageResource(data.getImageId());
        dataTv.setText(data.getName());
        return view;
    }
}

MainActivity找到ListView并为其添加适配器

public class MainActivity extends AppCompatActivity {
    
    private List dataList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initData();
        DataAdapter adapter = new DataAdapter(MainActivity.this, R.layout.list_item, dataList);
        ListView listView = findViewById(R.id.list_view);
        listView.setAdapter(adapter);

    }

    private void initData() {
        for (int i = 0; i < 15; i++) {
            Data data = new Data("data" + i, R.mipmap.ic_launcher);
            dataList.add(data);
        }
    }
}

上面的DataAdapter每次通过findViewById查找View，可通过引入ViewHolder提升效率

public class DataAdapter extends ArrayAdapter {

    private int resourceId;

    public DataAdapter(@NonNull Context context, int resource, @NonNull List objects) {
        super(context, resource, objects);
        resourceId = resource;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        Data data = getItem(position);
        View view;
        ViewHolder viewHolder;
        if (convertView == null) {
            view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
            viewHolder = new ViewHolder();
            viewHolder.dataIv = view.findViewById(R.id.list_iv);
            viewHolder.dataTv = view.findViewById(R.id.list_tv);
            view.setTag(viewHolder);
        } else {
            view = convertView;
            viewHolder = (ViewHolder) view.getTag();
        }

        viewHolder.dataIv.setImageResource(data.getImageId());
        viewHolder.dataTv.setText(data.getName());
        return view;
    }

    private class ViewHolder {
        ImageView dataIv;
        TextView dataTv;
    }
}

BaseAdapter

public class DataAdapter extends BaseAdapter {

    private List mData;
    private LayoutInflater mInflater;

    public DataAdapter(Context context, List data) {
        mData = data;
        mInflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return mData.size();
    }

    @Override
    public Object getItem(int position) {
        return mData.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        if (convertView == null) {
            holder = new ViewHolder();
            convertView = mInflater.inflate(R.layout.list_item, null);
            holder.dataIv = convertView.findViewById(R.id.list_iv);
            holder.dataTv = convertView.findViewById(R.id.list_tv);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        Data data = (Data) getItem(position);
        holder.dataIv.setImageResource(data.getImageId());
        holder.dataTv.setText(data.getName());
        return convertView;
    }


    private class ViewHolder {
        ImageView dataIv;
        TextView dataTv;
    }
}

Listener

点击事件

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView parent, View view, int position, long id) {
                Toast.makeText(MainActivity.this, dataList.get(position).getName(), Toast.LENGTH_SHORT).show();
            }
        });

点击时默认会改变背景颜色，可通过如下属性取消

android:listSelector="@android:color/transparent"
android:listSelector="#00000000"

触摸事件

listView.setOnTouchListener(new View.OnTouchListener() {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                break;
            case MotionEvent.ACTION_MOVE:
                break;
            case MotionEvent.ACTION_UP:
                break;
        }
        return false;
    }
});

滑动事件

有三种滑动类型，在滑动时还可以通过onScroll()判断当前位置、方向

private int lastVisibleItemPosition;

listView.setOnScrollListener(new AbsListView.OnScrollListener() {
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        switch (scrollState) {
            case SCROLL_STATE_IDLE: //滑动停止
                break;
            case SCROLL_STATE_TOUCH_SCROLL://正在滑动
                break;
            case SCROLL_STATE_FLING:    //手指抛甩，惯性滑动
                break;
        }
    }
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        //firstVisibleItem 当前可视的第一个item
        //visibleItemCount 当前可视的item总数，包括未显示完全的item
        if (totalItemCount > 0 && firstVisibleItem + visibleItemCount == totalItemCount) {
            //滑动到最后一行
        }
        if (firstVisibleItem > lastVisibleItemPosition) {
            //上滑
        } else if (firstVisibleItem < lastVisibleItemPosition) {
            //下滑
        }
        lastVisibleItemPosition = firstVisibleItem;
    }
});
listView.getFirstVisiblePosition();		//获取当前可视部分第一个Item ID
listView.getLastVisiblePosition();		//获取当前可视部分最后一个Item ID

分割线和滚动条

可通过如下属性设置颜色和大小

android:divider="@color/colorPrimaryDark"
android:dividerHeight="5dp"

如下属性取消滚动条

android:scrollbars="none"

显示第几项

默认显示第一个Item，可通过如下方法设置显示，如显示第五项

listView.setSelection(5);

动态更新数据

每当数据变化时，可通过如下方式动态更新ListView

dataList.add(new Data("data100", R.mipmap.ic_launcher));
adapter.notifyDataSetChanged();

处理空ListView

当列表为空时，ListView不会显示任何提示，可通过如下方式设置无数据时的提示，其可以是任何View

listView.setEmptyView();

扩展

弹性效果

默认ListView滑到顶部或尾部只会出现一个半弧形提示，如下

并不会弹性继续滑动，可通过重写overScrollBy()设置maxOverScrollY实现弹性回滚

public class MyListView extends ListView {
    private int mMaxOverDistance = 100;

    public MyListView(Context context) {
        this(context, null);
        DisplayMetrics metrics = context.getResources().getDisplayMetrics();
        float density = metrics.density;
        mMaxOverDistance = (int) (density * mMaxOverDistance);
    }

    public MyListView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public MyListView(Context context, AttributeSet attrs, int defStyleAttr) {
        this(context, attrs, defStyleAttr, 0);
    }

    public MyListView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    protected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, int scrollRangeX, int scrollRangeY, int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {
        return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, mMaxOverDistance, isTouchEvent);
    }
}

效果如下图

自动显示、隐藏布局

（适配器、数据、适配布局同上），如下实现在滚动时隐藏标题栏，需要添加一个HeadView，避免第一个Item被Topbar遮挡

public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getSimpleName();
    private List dataList = new ArrayList<>();
    private float mFirstY;
    private float mCurrentY;
    private boolean isScrollDown;
    private boolean mShow = true;
    private Animator mAnimator;
    private int mTouchSlop;
    private Toolbar mToolbar;
    private ListView mListView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        initData();
        addAdapter();
        addHeaderView();
        addListener();
    }

    private void initView() {
        mListView = findViewById(R.id.list_view);
        mToolbar = findViewById(R.id.tb);
    }

    private void addListener() {
        mListView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        mFirstY = event.getY();
                        break;
                    case MotionEvent.ACTION_MOVE:
                        mCurrentY = event.getY();
                        if (mCurrentY - mFirstY > mTouchSlop) {
                            isScrollDown = true; //下滑，Y不断变大
                        } else {
                            isScrollDown = false; //上滑，Y不断变小
                        }
                        toolbarAnim(isScrollDown);
                        mShow = !mShow;
                        break;
                    case MotionEvent.ACTION_UP:
                        break;
                }
                return false;
            }
        });
    }

    private void addHeaderView() {
        View header = new View(this);
        /*TypedValue tv = new TypedValue();
        int actionBarHeight = 0;
        if (this.getTheme().resolveAttribute(android.R.attr.actionBarSize, tv, true)) {
            actionBarHeight = TypedValue.complexToDimensionPixelSize(tv.data, this.getResources().getDisplayMetrics());
        }
        Log.d(TAG, "onCreate: actionBarHeight = " + actionBarHeight);
        header.setLayoutParams(new AbsListView.LayoutParams(
                AbsListView.LayoutParams.MATCH_PARENT,
                actionBarHeight));*/
        header.setLayoutParams(new AbsListView.LayoutParams(AbsListView.LayoutParams.MATCH_PARENT,
                (int) getResources().getDimension(R.dimen.abc_action_bar_default_height_material)));//获取属性Actionbar的高度
        mListView.addHeaderView(header);
    }

    private void addAdapter() {
        DataAdapter adapter = new DataAdapter(MainActivity.this, dataList);
        mListView.setAdapter(adapter);
    }

    private void toolbarAnim(boolean isScrollDown) {
        if (mAnimator != null && mAnimator.isRunning()) {
            mAnimator.cancel();
        }
        Log.d(TAG, "toolbarAnim: isScrollDown = " + isScrollDown);
        Log.d(TAG, "toolbarAnim: mToolbar.getTranslationY() = " + mToolbar.getTranslationY());
        Log.d(TAG, "toolbarAnim: -mToolbar.getHeight() = " + -mToolbar.getHeight());
        if (isScrollDown) {    //下滑的时候，显示标题栏，即将滑动的Y递减为0
            mAnimator = ObjectAnimator.ofFloat(mToolbar,
                    "translationY", mToolbar.getTranslationY(), 0);
        } else {    //上滑，隐藏标题栏，即减去Toolbar高度
            /*mAnimator = ObjectAnimator.ofFloat(mToolbar,
                    "translationY", mToolbar.getTranslationY(), -mToolbar.getHeight()); */
            mAnimator = ObjectAnimator.ofFloat(mToolbar,
                    "translationY", 0, -mToolbar.getHeight());
        }
        mAnimator.start();
    }

    private void initData() {
        for (int i = 0; i < 30; i++) {
            Data data = new Data("data" + i, R.mipmap.ic_launcher);
            dataList.add(data);
        }
        mTouchSlop = ViewConfiguration.get(this).getScaledTouchSlop(); //获取系统最短滑动距离，根据此判断是否滑动
    }
}

布局如下

manifest中将theme设置为NoActionBar

android:theme="@style/Theme.AppCompat.DayNight.NoActionBar"

效果如图，下滑时隐藏Topbar，上滑时显示

聊天布局

在上面的Data Bean类再加上type及其构造函数

private int type;

public int getType() {
    return type;
}
public void setType(int type) {
    this.type = type;
}

public Data(String name, int imageId, int type) {
        this.name = name;
        this.imageId = imageId;
        this.type = type;
    }

创建相反布局list_item2.xml

在适配器中重写getItemViewType和getViewTypeCount，在getView根据type初始化布局

@Override
public int getItemViewType(int position) {
    Data data = mData.get(position);
    return data.getType();
}

@Override
public int getViewTypeCount() {
    return 2;
}

@Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        if (convertView == null) {
            holder = new ViewHolder();
            if (getItemViewType(position) == 0) {
                convertView = mInflater.inflate(R.layout.list_item, null);
            } else {
                convertView = mInflater.inflate(R.layout.list_item2, null);
            }
            holder.dataIv = convertView.findViewById(R.id.list_iv);
            holder.dataTv = convertView.findViewById(R.id.list_tv);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        Data data = (Data) getItem(position);
        holder.dataIv.setImageResource(data.getImageId());
        holder.dataTv.setText(data.getName());
        return convertView;
    }

在创建数据时，加入type

private void initData() {
        boolean type = true;
        for (int i = 0; i < 30; i++) {
            Data data = new Data("data" + i, R.mipmap.ic_launcher, type ? 0 : 1);
            dataList.add(data);
            type = !type;
        }
        mTouchSlop = ViewConfiguration.get(this).getScaledTouchSlop(); //获取系统最短滑动距离，根据此判断是否滑动
    }

效果如下

动态改变布局

实现当Item被选中时，让其布局发生改变，如下为xml

Adapter的getView()方法根据当前Item选择布局

public class DataAdapter extends BaseAdapter {

    private Context mContext;
    private List mData;

    public void setCurrentItem(int currentItem) {
        mCurrentItem = currentItem;
    }

    private int mCurrentItem;

    public DataAdapter(Context context, List data) {
        mData = data;
        mContext = context;
    }

    @Override
    public int getCount() {
        return mData.size();
    }

    @Override
    public Object getItem(int position) {
        return mData.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LinearLayout layout = new LinearLayout(mContext);
        layout.setOrientation(LinearLayout.VERTICAL);
        if (mCurrentItem == position) {
            layout.addView(addFocusView());
        } else {
            layout.addView(addNormalView(position));
        }
        return layout;
    }

    private View addFocusView() {
        ImageView iv = new ImageView(mContext);
        iv.setImageResource(R.mipmap.ic_launcher);
        return iv;
    }

    private View addNormalView(int i) {
        LinearLayout layout = new LinearLayout(mContext);
        layout.setOrientation(LinearLayout.HORIZONTAL);
        ImageView iv = new ImageView(mContext);
        iv.setImageResource(mData.get(i).getImageId());
        layout.addView(iv, new LinearLayout.LayoutParams(
                ViewGroup.LayoutParams.WRAP_CONTENT,
                ViewGroup.LayoutParams.WRAP_CONTENT
        ));
        TextView tv = new TextView(mContext);
        tv.setText(mData.get(i).getName());
        layout.addView(tv, new LinearLayout.LayoutParams(
                ViewGroup.LayoutParams.WRAP_CONTENT,
                ViewGroup.LayoutParams.WRAP_CONTENT
        ));
        return layout;
    }
}

MainActivity中为ListView设置点击事件，点击时通知Adapter重写加载

public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getSimpleName();
    private List dataList = new ArrayList<>();
    private ListView mListView;
    private DataAdapter mAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        initData();
        addListener();
    }

    private void initView() {
        mListView = findViewById(R.id.list_view);
    }

    private void addListener() {
        mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView parent, View view, int position, long id) {
                mAdapter.setCurrentItem(position);
                mAdapter.notifyDataSetChanged();
            }
        });
    }

    private void initData() {
        for (int i = 0; i < 30; i++) {
            Data data = new Data("data" + i, R.mipmap.ic_launcher);
            dataList.add(data);
        }
        mAdapter = new DataAdapter(this, dataList);
        mListView.setAdapter(mAdapter);
    }
}

效果如图