android - 当拖动 Imageview 到屏幕外时

Question

我想在拖动时实现一个可移动的imageView。拖动工作正常。但是当我拖到最后时，imageView 会离开屏幕。 如何让 imageview 只在屏幕内移动？

这是我的 OnTouch 监听器:

public boolean onTouch(View view, MotionEvent event) {
    switch (event.getActionMasked()) {
      case MotionEvent.ACTION_DOWN:
        dX = view.getX() - event.getRawX();
        dY = view.getY() - event.getRawY();
        lastAction = MotionEvent.ACTION_DOWN;
        break;

      case MotionEvent.ACTION_MOVE:
        view.setY(event.getRawY() + dY);
        view.setX(event.getRawX() + dX);
        lastAction = MotionEvent.ACTION_MOVE;
        break;

      case MotionEvent.ACTION_UP:
        if (lastAction == MotionEvent.ACTION_DOWN)
          Toast.makeText(DraggableView.this, "Clicked!", Toast.LENGTH_SHORT).show();
        break;

      default:
        return false;
    }
    return true;
  }

这是我的布局。布局包含一个 ScrollView 及其 subview ，以及我要拖动的 ImageView 。

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clickable="true" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical" >

            <TextView
                android:layout_width="match_parent"
                android:layout_height="400dp"
                android:background="#ff0000"
                android:gravity="center"
                android:text="View 1"
                android:textColor="#000"
                android:textSize="100dp" />

            <TextView
                android:layout_width="match_parent"
                android:layout_height="400dp"
                android:background="#00ff00"
                android:text="View 2"
                android:textColor="#000"
                android:textSize="100dp" />  
        </LinearLayout>
    </ScrollView>

    <ImageView
        android:id="@+id/draggable_view"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_gravity="bottom|right"
        android:layout_marginBottom="20dp"
        android:layout_marginEnd="20dp"
        android:background="@drawable/icon" />

</FrameLayout>

Answer 1

花了更多的时间，终于找到了最好的解决方案。

将我的 OnTouch 监听器部分修改为:

 DisplayMetrics displaymetrics = new DisplayMetrics();
 getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
 screenHight = displaymetrics.heightPixels;
 screenWidth = displaymetrics.widthPixels;

  @SuppressLint("NewApi") @Override
  public boolean onTouch(View view, MotionEvent event) {


       float newX, newY;

    switch (event.getActionMasked()) {
      case MotionEvent.ACTION_DOWN:

        dX = view.getX() - event.getRawX();
        dY = view.getY() - event.getRawY();
        lastAction = MotionEvent.ACTION_DOWN;
        break;

      case MotionEvent.ACTION_MOVE:

          newX = event.getRawX() + dX;
          newY = event.getRawY() + dY;

      // check if the view out of screen
          if ((newX <= 0 || newX >= screenWidth-view.getWidth()) || (newY <= 0 || newY >= screenHight-view.getHeight()))
          {
              lastAction = MotionEvent.ACTION_MOVE;
              break;      
          }

        view.setX(newX);
        view.setY(newY);

        lastAction = MotionEvent.ACTION_MOVE;

        break;

      case MotionEvent.ACTION_UP:
        if (lastAction == MotionEvent.ACTION_DOWN)
          Toast.makeText(DraggableView.this, "Clicked!", Toast.LENGTH_SHORT).show();
        break;

      default:
        return false;
    }
    return true;
  }

它运行完美:)