微信联系人右首字母滑动索引

实现思路：通过自定义View在频幕右侧循环写入a~z;复写onTouchEvent

 @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_MOVE:
                 break;
            case MotionEvent.ACTION_DOWN:
                 break;
            case MotionEvent.ACTION_UP:             
                 break;
        }

点击的时候获取点击的字母传给 listener.onItemSelect(index, array[index]);
使用观察者模式` //观察者模式
public interface OnItemSelect {
public void onItemSelect(int index, String indexString);
}

private OnItemSelect listener;

public void setOnItemSelectListener(OnItemSelect listener) {
    this.listener = listener;
}`

在MainActivity当中

mySlider.setOnItemSelectListener(new MySlider.OnItemSelect(){


            @Override
            public void onItemSelect(int index, String indexString) {
                textView.setText(indexString);
            }
        });

将字母赋给textView

通过自定义View实现，代码及注释如下

自定义View

public class MySlider extends View {
    private String[] array = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"};
    private int width;
    private int height;
    private Paint paint;
    private Paint paintTouch;
    private int index = -1;



    //观察者模式
    public interface OnItemSelect {
        public void onItemSelect(int index, String indexString);
    }

    private OnItemSelect listener;

    public void setOnItemSelectListener(OnItemSelect listener) {
        this.listener = listener;
    }


    public MySlider(Context context, AttributeSet attrs) {
        super(context, attrs);
        paint = new Paint();
        paint.setTextAlign(Paint.Align.CENTER);
        paint.setTextSize(30);

        paintTouch = new Paint();
        paintTouch.setColor(Color.GREEN);
        paintTouch.setTextSize(32);

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);
        height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        setMeasuredDimension(width, height);
    }

    private float x;
    private float y;

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_MOVE:
            case MotionEvent.ACTION_DOWN:
                x = event.getX();
                y = event.getY();
                if (x > width - paint.measureText("m") * 2) {
                    index = (int) y / (height / 26);
                    Log.d("", "点击的字母" + array[index]);

                    if (listener != null) {
                        listener.onItemSelect(index, array[index]);
                    }
                    invalidate();
                    return true;
                }
                break;
            case MotionEvent.ACTION_UP:
                index = -1;
                invalidate();

                break;
        }


        return super.onTouchEvent(event);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        for (int i = 0; i < 26; i++) {
            if (index == i) {
                canvas.drawText("" + array[i], width - paint.measureText("m"), height / 26 * (i + 1), paintTouch);
            } else {
                canvas.drawText("" + array[i], width - paint.measureText("m"), height / 26 * (i + 1), paint);
            }

        }

    }
}

Activity

public class MainActivityMySlider extends Activity {


    private MySlider mySlider;
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_mainmyslider);
        //mySlider既是一个控件又是类名
        mySlider= (MySlider) findViewById(R.id.myslider);
        textView= (TextView) findViewById(R.id.textview);
        mySlider.setOnItemSelectListener(new MySlider.OnItemSelect(){


            @Override
            public void onItemSelect(int index, String indexString) {
                textView.setText(indexString);
            }
        });

    }
}

XML布局

<?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">
    <com.example.administrator.canvas.widget.MySlider
        android:id="@+id/myslider"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>


    <TextView
        android:id="@+id/textview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="A"
        android:textSize="200dp"/>



</RelativeLayout>