Kéo view đến một vị trí xác định

Ta đã có thể kéo view tự do trên màn hình. Bây giờ ta muốn kéo view đến vị trí nhất định, view sẽ dừng đúng vị trí đó, chưa đúng vị trí nó sẽ bật lại vị trí ban đầu.

Tạo một file keo.xml trong layout như sau.

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical"

android:padding="10dp"

android:paddingLeft="50dp"

android:paddingRight="50dp" >

<TextView

android:id="@+id/option_1"

android:layout_width="fill_parent"

android:layout_height="50dp"

android:layout_margin="5dp"

android:background="#00ffff"

android:gravity="center"

android:text="Apple"

android:textStyle="bold" />

<TextView

android:id="@+id/option_2"

android:layout_width="fill_parent"

android:layout_height="50dp"

android:layout_margin="5dp"

android:background="#0000ff"

android:gravity="center"

android:text="Orange"

android:textStyle="bold" />

<TextView

android:id="@+id/option_3"

android:layout_width="fill_parent"

android:layout_height="50dp"

android:layout_margin="5dp"

android:background="#008000"

android:gravity="center"

android:text="Ball"

android:textStyle="bold" />

<TextView

android:id="@+id/choice_1"

android:layout_width="fill_parent"

android:layout_height="50dp"

android:layout_margin="5dp"

android:background="#00ffff"

android:gravity="center"

android:text="A for " />

<TextView

android:id="@+id/choice_2"

android:layout_width="fill_parent"

android:layout_height="50dp"

android:layout_margin="5dp"

android:background="#00ffff"

android:gravity="center"

android:text="O for " />

<TextView

android:id="@+id/choice_3"

android:layout_width="fill_parent"

android:layout_height="50dp"

android:layout_margin="5dp"

android:background="#00ffff"

android:gravity="center"

android:text="B for " />

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_gravity="center"

android:text="Reset"

android:onClick="reset"/>

</LinearLayout>

Class điều khiển như sau.

public class keoview extends Activity {

private TextView option1, option2, option3, choice1, choice2, choice3;

public CharSequence dragData;

@TargetApi(Build.VERSION_CODES.HONEYCOMB)

@SuppressLint("NewApi")

@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.keo);

    //get both sets of text views

    //views to drag

    option1 = (TextView)findViewById(R.id.option_1);

    option2 = (TextView)findViewById(R.id.option_2);

    option3 = (TextView)findViewById(R.id.option_3);

    //views to drop onto

    choice1 = (TextView)findViewById(R.id.choice_1);

    choice2 = (TextView)findViewById(R.id.choice_2);

    choice3 = (TextView)findViewById(R.id.choice_3);

    //set touch listeners

    option1.setOnTouchListener(new ChoiceTouchListener());

    option2.setOnTouchListener(new ChoiceTouchListener());

    option3.setOnTouchListener(new ChoiceTouchListener());

    //set drag listeners

    choice1.setOnDragListener(new ChoiceDragListener());

    choice2.setOnDragListener(new ChoiceDragListener());

    choice3.setOnDragListener(new ChoiceDragListener());

}

private final class ChoiceTouchListener implements OnTouchListener {

    @SuppressLint("NewApi")

    @Override

    public boolean onTouch(View view, MotionEvent motionEvent) {

        if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {

            ClipData data = ClipData.newPlainText("", "");

            DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);

            //start dragging the item touched

            view.startDrag(data, shadowBuilder, view, 0);

            return true;

        } else {

            return false;

        }

    }

}

@SuppressLint("NewApi")

private class ChoiceDragListener implements OnDragListener {

    @Override

    public boolean onDrag(View v, DragEvent event) {

        switch (event.getAction()) {

        case DragEvent.ACTION_DRAG_STARTED:

            //no action necessary

            break;

        case DragEvent.ACTION_DRAG_ENTERED:

            //no action necessary

            break;

        case DragEvent.ACTION_DRAG_EXITED:       

            //no action necessary

            break;

        case DragEvent.ACTION_DROP:

            View view = (View) event.getLocalState();

            //view dragged item is being dropped on

            TextView dropTarget = (TextView) v;

            //view being dragged and dropped

            TextView dropped = (TextView) view;

            //checking whether first character of dropTarget equals first character of dropped

            if(dropTarget.getText().toString().charAt(0) == dropped.getText().toString().charAt(0))

            {

                //stop displaying the view where it was before it was dragged

                view.setVisibility(View.INVISIBLE);

                //update the text in the target view to reflect the data being dropped

                dropTarget.setText(dropTarget.getText().toString() + dropped.getText().toString());

                //make it bold to highlight the fact that an item has been dropped

                dropTarget.setTypeface(Typeface.DEFAULT_BOLD);

                //if an item has already been dropped here, there will be a tag

                Object tag = dropTarget.getTag();

                //if there is already an item here, set it back visible in its original place

                if(tag!=null)

                {

             //the tag is the view id already dropped here

                    int existingID = (Integer)tag;

                    //set the original view visible again

                    findViewById(existingID).setVisibility(View.VISIBLE);

                }

                //set the tag in the target view being dropped on - to the ID of the view being dropped

                dropTarget.setTag(dropped.getId());

                //remove setOnDragListener by setting OnDragListener to null, so that no further drag & dropping on this TextView can be done

                dropTarget.setOnDragListener(null);

            }

            else

                //displays message if first character of dropTarget is not equal to first character of dropped

                Toast.makeText(keo3.this, dropTarget.getText().toString() + "is not " + dropped.getText().toString(), Toast.LENGTH_LONG).show();

            break;

        case DragEvent.ACTION_DRAG_ENDED:

            break;

        default:

            break;

        }

        return true;

    }

}

public void reset(View view)

{

    option1.setVisibility(TextView.VISIBLE);

    option2.setVisibility(TextView.VISIBLE);

    option3.setVisibility(TextView.VISIBLE);

    choice1.setText("A for ");

    choice2.setText("O for ");

    choice3.setText("B for ");

    choice1.setTag(null);

    choice2.setTag(null);

    choice3.setTag(null);

    choice1.setTypeface(Typeface.DEFAULT);

    choice2.setTypeface(Typeface.DEFAULT);

    choice3.setTypeface(Typeface.DEFAULT);

    choice1.setOnDragListener(new ChoiceDragListener());

    choice2.setOnDragListener(new ChoiceDragListener());

    choice3.setOnDragListener(new ChoiceDragListener());

}

}

Tôi giữ lại một số dòng giải thích gốc để bạn tự đọc.

Cách này có thể vận dụng mở rộng để làm game.