1.前言

在開發中，會有需求實現控制元件在螢幕隨意拖動，這就需要自定義View,然後在OnTouchEvent事件中，處理MotionEvent.ACTION_MOVE事件，然後通過座標點傳值給onlayout方法,來實現控制元件的任意拖動，具體程式碼如下：

import android.content.Context;
import android.util.AttributeSet;
import android.view.Display;
import android.view.MotionEvent;
import android.view.WindowManager;
import android.widget.LinearLayout;

public class DragLineLayout extends LinearLayout {

  private int mWidth;
  private int mHeight;
  private int mScreenWidth;
  private int mScreenHeight;
  private Context mContext;
  private onLocationListener mLocationListener;/*listen to the Rect */
  //是否拖動
  private boolean isDrag = false;

  public boolean isDrag() {
    return isDrag;
  }

  public DragView(Context context,AttributeSet attrs) {
    super(context,attrs);
    this.mContext = context;
  }

  @Override
  protected void onMeasure(int widthMeasureSpec,int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec,heightMeasureSpec);
    mWidth = getMeasuredWidth();
    mHeight = getMeasuredHeight();
    mScreenWidth = getScreenWidth(mContext);
    mScreenHeight = getScreenHeight(mContext) - getStatusBarHeight();
  }

  public int getStatusBarHeight() {
    int resourceId = mContext.getResources().getIdentifier("status_bar_height","dimen","android");
    return mContext.getResources().getDimensionPixelSize(resourceId);
  }

  public int getScreenWidth(Context context) {
    WindowManager manager = (WindowManager) context
        .getSystemService(Context.WINDOW_SERVICE);
    Display display = manager.getDefaultDisplay();
    return display.getWidth();
  }

  public int getScreenHeight(Context context) {
    WindowManager manager = (WindowManager) context
        .getSystemService(Context.WINDOW_SERVICE);
    Display display = manager.getDefaultDisplay();
    return display.getHeight();
  }

  private float mDownX;
  private float mDownY;


  @Override
  public boolean onTouchEvent(MotionEvent event) {
    super.onTouchEvent(event);
    if (this.isEnabled()) {
      switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
          isDrag = false;
          mDownX = event.getX();
          mDownY = event.getY();
          break;
        case MotionEvent.ACTION_MOVE:
          final float mXdistance = event.getX() - mDownX;
          final float mYdistance = event.getY() - mDownY;
          int l,r,t,b;
          //當水平或者垂直滑動距離大於10,才算是拖動事件
          if (Math.abs(mXdistance) > 10 || Math.abs(mYdistance) > 10) {
            isDrag = true;
            l = (int) (getLeft() + mXdistance);
            r = l + mWidth;
            t = (int) (getTop() + mYdistance);
            b = t + mHeight;
            //邊界判斷,不讓佈局滑出介面
            if (l < 0) {
              l = 0;
              r = l + mWidth;
            } else if (r > mScreenWidth) {
              r = mScreenWidth;
              l = r - mWidth;
            }
            if (t < 0) {
              t = 0;
              b = t + mHeight;
            } else if (b > mScreenHeight) {
              b = mScreenHeight;
              t = b - mHeight;
            }
            //回撥移動後的座標點
            if(mLocationListener!=null){
              mLocationListener.locationRect((l+r)/2,(t+b)/2);
            }
            this.layout(l,b);
          }
          break;
        case MotionEvent.ACTION_UP:
          setPressed(false);
          break;
        case MotionEvent.ACTION_CANCEL:
          setPressed(false);
          break;
      }
      return true;
    }
    return false;
  }
  public void setLocationListener(onLocationListener LocationListener) {
    this.mLocationListener = LocationListener;
  }
  public interface onLocationListener {
    void locationRect(float locationX,float locationY);
  }
}

2.在程式碼中的運用

<com.xinrui.guestservice.view.DragLineLayout 
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="@dimen/dp_200"
  android:layout_height="@dimen/dp_110"
  android:orientation="vertical">
  <RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="@dimen/dp_50">
  <EditText
    android:id="@+id/input_edt"
    android:layout_width="match_parent"
    android:layout_height="@dimen/dp_50"
    android:background="@drawable/edit_bg" />
  </RelativeLayout>
  <RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="@dimen/dp_55"
    android:layout_marginTop="@dimen/margin_5"
    android:background="@drawable/paint_bg">

    <TextView
      android:id="@+id/paint_typeface"
      android:layout_width="@dimen/dp_50"
      android:layout_height="@dimen/dp_50"
      android:layout_alignParentLeft="true"
      android:layout_alignParentTop="true"
      android:layout_marginTop="@dimen/margin_5"
      android:background="@drawable/main_selector_write"
      android:clickable="true" />

    <TextView
      android:id="@+id/paint_fontsize"
      android:layout_width="@dimen/dp_50"
      android:layout_height="@dimen/dp_50"
      android:layout_alignParentTop="true"
      android:layout_marginLeft="@dimen/dp_10"
      android:layout_marginTop="@dimen/margin_5"
      android:layout_toRightOf="@id/paint_typeface"
      android:background="@drawable/main_selector_write"
      android:clickable="true" />
  </RelativeLayout>
</com.xinrui.guestservice.view.DragLineLayout>

3.這樣就可以在Activity 載入這個xml 來實現任意拖動功能

總結

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