将按钮保持在边界内

Question

我仍然是 android 编程的新手（比如 3 周大），但我正在慢慢掌握事情的窍门。我在不同的网站上寻找答案，但我还没有找到任何答案。

到目前为止我的 Java 代码（至少是相关的）：

view = (ImageView)findViewById(R.id.imageView3);
backgroundImageName = String.valueOf(view.getTag());

view.setOnTouchListener(new View.OnTouchListener() {
    public boolean onTouch(View v, MotionEvent event) {
        int myNewX = (int)event.getX(); //this line and the next get the X & Y coordinates of wherever the mouse clicked
        int myNewY = (int)event.getY();
        Button button = (Button)findViewById(R.id.add_text);

        // find a way to keep the button within the borders of the white square
        if (event.getAction() == MotionEvent.ACTION_UP) { //checks if the mouse click was released
            button.setVisibility(View.VISIBLE);
            button.setX(myNewX - 160); //this line and the next set the coordinates of the button (plus the adjustment)
            button.setY(myNewY + 70); //to make the button by above and in the middle of where the mouse clicked
        }
        else
        {
            button.setVisibility(View.INVISIBLE);
        }
        return true;
    }
});

到目前为止我的 XML 代码（至少是相关的）：

<ImageView
    android:id="@+id/imageView3"
    android:layout_width="450dp"
    android:layout_height="450dp"
    android:layout_marginBottom="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginRight="8dp"
    android:layout_marginTop="8dp"
    android:contentDescription="@string/white_background"
    android:tag="white"
    android:visibility="invisible"
    app:layout_constraintBottom_toBottomOf="@+id/button"
    app:layout_constraintLeft_toLeftOf="@+id/imageView2"
    app:layout_constraintRight_toRightOf="@+id/imageView2"
    app:layout_constraintTop_toTopOf="@+id/textView"
    app:srcCompat="@mipmap/white" />

<Button
    android:id="@+id/add_text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/add_text"
    android:visibility="invisible"
    tools:ignore="MissingConstraints"
    tools:layout_editor_absoluteY="71dp"
    tools:layout_editor_absoluteX="16dp" />

我想要做的是将按钮保持在图片所示的边界内，但我不知道如何做到这一点。我知道它应该如何工作是：

If mouseclick (the event) is outside the border { set the x coordinate of the button to the edge of the border and the same for the y coordinate }

我一直试图让它正常工作，但它只是拒绝。如果有人可以帮助我找出使其工作所需的代码，我将非常感谢您的帮助。

谢谢

Answer 1

首先创建边界检查，然后执行您的任务：

view.setOnTouchListener(new View.OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
    //obtain the boundaries of the view
    if(event.getAction() == MotionEvent.ACTION_DOWN){
    rect = new Rect(v.getLeft(), v.getTop(), v.getRight(), v.getBottom());

    }
    if (event.getAction() == MotionEvent.ACTION_UP){
       //Catches out of boundary user's movement.
       if(!rect.contains(v.getLeft() + (int) event.getX(), v.getTop() + 
        (int) event.getY())){

       button.setVisibility(View.VISIBLE);
       //perform your other calculations

    }

    return true;
}

});

注意：从 API 14 开始，您可以使用：Android MotionEvent 的 ACTION_HOVER_ENTER： https://developer.android.com/reference/android/view/MotionEvent.html#ACTION_HOVER_ENTER