Android觸控事件

觸控事件
MotionEvent類：

  //單擊觸摸按下動作
   public static final int ACTION_DOWN             = 0;

    /**
     * Constant for {@link #getActionMasked}: A pressed gesture has finished, the
     * motion contains the final release location as well as any intermediate
     * points since the last down or move event.
     * 單擊觸摸離開動作
     */
    public static final int ACTION_UP               = 1;

    /**
     * Constant for {@link #getActionMasked}: A change has happened during a
     * press gesture (between {@link #ACTION_DOWN} and {@link #ACTION_UP}).
     * The motion contains the most recent point, as well as any intermediate
     * points since the last down or move event.
     * 觸摸點移動動作
     */
    public static final int ACTION_MOVE             = 2;

    /**
     * Constant for {@link #getActionMasked}: The current gesture has been aborted.
     * You will not receive any more points in it.  You should treat this as
     * an up event, but not perform any action that you normally would.
     * 觸摸動作取消
     */
    public static final int ACTION_CANCEL           = 3;

    /**
     * Constant for {@link #getActionMasked}: A movement has happened outside of the
     * normal bounds of the UI element.  This does not provide a full gesture,
     * but only the initial location of the movement/touch.
     * 觸摸動作超出邊界
     */
    public static final int ACTION_OUTSIDE          = 4;

    /**
     * Constant for {@link #getActionMasked}: A non-primary pointer has gone down.
     * <p>
     * Use {@link #getActionIndex} to retrieve the index of the pointer that changed.
     * </p><p>
     * The index is encoded in the {@link #ACTION_POINTER_INDEX_MASK} bits of the
     * unmasked action returned by {@link #getAction}.
     * </p>
     * 多點觸摸按下動作
     */
    public static final int ACTION_POINTER_DOWN     = 5;

    /**
     * Constant for {@link #getActionMasked}: A non-primary pointer has gone up.
     * <p>
     * Use {@link #getActionIndex} to retrieve the index of the pointer that changed.
     * </p><p>
     * The index is encoded in the {@link #ACTION_POINTER_INDEX_MASK} bits of the
     * unmasked action returned by {@link #getAction}.
     * </p>
     * 多點離開動作
     */
    public static final int ACTION_POINTER_UP       = 6;

MotionEvent提供的方法：

getTop():獲取到的是View自身的頂邊到其父布局頂邊的距離。
getLeft():獲取到的是View自身的左邊到其父布局左邊的距離。
getRight():獲取到的是View自身的右邊到其父布局右邊的距離。
getBottom():獲取到的是View自身的底邊到其父布局底邊的距離。


getX():獲取點擊事件距離控件左邊的距離
getY():獲取點擊事件距離控件頂邊的距離
getRawX():獲取點擊事距離整個屏幕左邊的距離，即絕對坐標。
getRawY():獲取點擊事距離整個屏幕頂邊的距離，即絕對坐標。

**實現滑動的基本原理（核心思想）：
當觸摸View時候，系統記錄當前觸摸點的坐標，當手指移動時候，系統記錄下移動的觸摸點坐標，從而獲取到相對於前一次坐標點的偏移量，並且通過偏移量修改view的坐標，這樣不斷重復，從而實現滑動效果。**
實現滑動的常用方法：
layout方法：

package com.example.drawdemo;

import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class MyView5 extends View {
    private int lastX;
    private int lastY;

    public MyView5(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView();
    }

    public MyView5(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public MyView5(Context context) {
        super(context);
        initView();
    }

    private void initView() {
        setBackgroundColor(Color.BLUE);
    }

    // 視圖坐標方式
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            lastX = x;
            lastY = y;
            break;
        case MotionEvent.ACTION_MOVE:
            // 計算偏移量
            int offsetX = x - lastX;
            int offsetY = y - lastY;
            layout(getLeft() + offsetX, getTop() + offsetY, getRight() + offsetX, getBottom() + offsetY);
            break;

        default:
            break;
        }

        return true;

    }
}

通過LayoutParams進行滑動。
LayoutParams 保存了一個View的布局參數，因此在程序中，通過改變LayoutParams修改一個布局的位置參數，從而達到改變View位置的效果。

而且我們可以使用getLayoutparams()來獲取一個View的LayoutParams.計算偏移量的方法與在Layout方法中計算offset也是一樣的，當獲取偏移量後，就可以通過setLayoutParams來改變Layoutparams.

當然獲取父容易布局，會有不同的布局（如果父容易是LinearLatyou，那麼就要使用LinearLayout.LayoutParams.如果是RelativeLayout,那麼就要使用RelativeLayout.LayoutParams.），所以我們直接使用ViewGroup.MarginLayoutParams來實現這個功能。

                    ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) getLayoutParams();
// LinearLayout.LayoutParams layoutParams =(LinearLayout.LayoutParams) getLayoutParams();
                    layoutParams.leftMargin = getLeft() + offsetX;
                    layoutParams.topMargin = getTop() + offsetY;

這個使用更加方便，不用考錄父容器布局。

package com.example.drawdemo;

import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

public class MyView6 extends View {
    private int lastX;
    private int lastY;

    public MyView6(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        // TODO Auto-generated constructor stub
        ininView();
    }

    public MyView6(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
        // TODO Auto-generated constructor stub
    }

    public MyView6(Context context) {
        super(context);
        ininView();
        // TODO Auto-generated constructor stub
    }

    private void ininView() {
         setBackgroundColor(Color.GREEN);

    }
       @Override
        public boolean onTouchEvent(MotionEvent event) {
            int x = (int) event.getX();
            int y = (int) event.getY();
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    // 記錄觸摸點坐標
                    lastX = (int) event.getX();
                    lastY = (int) event.getY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    // 計算偏移量
                    int offsetX = x - lastX;
                    int offsetY = y - lastY;
                    ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) getLayoutParams();
//                  LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) getLayoutParams();
                    layoutParams.leftMargin = getLeft() + offsetX;
                    layoutParams.topMargin = getTop() + offsetY;
                    setLayoutParams(layoutParams);
                    break;
            }
            return true;
        }
}

通過scrollTo與scorllBy進行滑動。
android 系統提供這個兩個方式進行改變一個View的位置
與前面的方法相同，也是計算偏移量。

package com.example.drawdemo;

import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class MyView7 extends View{


    private int lastX;
    private int lastY;

    public MyView7(Context context) {
        super(context);
        ininView();
    }

    public MyView7(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
    }

    public MyView7(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        ininView();
    }

    private void ininView() {
        setBackgroundColor(Color.YELLOW);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastX = (int) event.getX();
                lastY = (int) event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                int offsetX = x - lastX;
                int offsetY = y - lastY;
                ((View) getParent()).scrollBy(-offsetX, -offsetY);
                break;
        }
        return true;
    }
}