如何在android studio中拖动imageview？ [复制]

Question

我正在使用本教程创建一个图像视图并将其拖到屏幕上

http://www.tutorialspoint.com/android/android_drag_and_drop.htm

但是当我在模拟器中拖动图像并放下它时，它消失了！我该如何解决？

这是我的布局文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Drag and Drop Example"
        android:id="@+id/textView"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:textSize="30dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Tutorials Point"
        android:id="@+id/textView2"
        android:layout_below="@+id/textView"
        android:layout_centerHorizontal="true"
        android:textSize="30dp"
        android:textColor="#ff14be3c" />>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView"
        android:src="@mipmap/ic_launcher"
        android:layout_below="@+id/textView2"
        android:layout_alignRight="@+id/textView2"
        android:layout_alignEnd="@+id/textView2"
        android:layout_alignLeft="@+id/textView2"
        android:layout_alignStart="@+id/textView2" />

</RelativeLayout>

这是我的 java 活动文件

import android.app.Activity;
import android.content.ClipData;
import android.content.ClipDescription;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.DragEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;
import android.widget.RelativeLayout;


public class MainActivity extends Activity {
    ImageView img;
    String msg;
    private android.widget.RelativeLayout.LayoutParams layoutParams;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        img=(ImageView)findViewById(R.id.imageView);

        img.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {
                ClipData.Item item = new ClipData.Item((CharSequence)v.getTag());
                String[] mimeTypes = {ClipDescription.MIMETYPE_TEXT_PLAIN};

                ClipData dragData = new ClipData(v.getTag().toString(),mimeTypes, item);
                View.DragShadowBuilder myShadow = new View.DragShadowBuilder(img);

                v.startDrag(dragData,myShadow,null,0);
                return true;
            }
        });

        img.setOnDragListener(new View.OnDragListener() {
            @Override
            public boolean onDrag(View v, DragEvent event) {
                switch(event.getAction())
                {
                    case DragEvent.ACTION_DRAG_STARTED:
                        layoutParams = (RelativeLayout.LayoutParams)v.getLayoutParams();
                        Log.d(msg, "Action is DragEvent.ACTION_DRAG_STARTED");

                        // Do nothing
                        break;

                    case DragEvent.ACTION_DRAG_ENTERED:
                        Log.d(msg, "Action is DragEvent.ACTION_DRAG_ENTERED");
                        int x_cord = (int) event.getX();
                        int y_cord = (int) event.getY();
                        break;

                    case DragEvent.ACTION_DRAG_EXITED :
                        Log.d(msg, "Action is DragEvent.ACTION_DRAG_EXITED");
                        x_cord = (int) event.getX();
                        y_cord = (int) event.getY();
                        layoutParams.leftMargin = x_cord;
                        layoutParams.topMargin = y_cord;
                        v.setLayoutParams(layoutParams);
                        break;

                    case DragEvent.ACTION_DRAG_LOCATION  :
                        Log.d(msg, "Action is DragEvent.ACTION_DRAG_LOCATION");
                        x_cord = (int) event.getX();
                        y_cord = (int) event.getY();
                        break;

                    case DragEvent.ACTION_DRAG_ENDED   :
                        Log.d(msg, "Action is DragEvent.ACTION_DRAG_ENDED");

                        // Do nothing
                        break;

                    case DragEvent.ACTION_DROP:
                        Log.d(msg, "ACTION_DROP event");

                        // Do nothing
                        break;
                    default: break;
                }
                return true;
            }
        });

        img.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                if (event.getAction() == MotionEvent.ACTION_DOWN) {
                    ClipData data = ClipData.newPlainText("", "");
                    View.DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(img);

                    img.startDrag(data, shadowBuilder, img, 0);
                    img.setVisibility(View.INVISIBLE);
                    return true;
                }
                else
                {
                    return false;
                }
            }
        });
    }

}

提前致谢！

Answer 1

我认为这是因为您设置了img.setVisibility(View.INVISIBLE)，但从未将其更改回可见状态。在您的 ACTION_DRAG_ENDED 部分中，尝试像这样再次使视图可见：

case DragEvent.ACTION_DRAG_ENDED   :
    Log.d(msg, "Action is DragEvent.ACTION_DRAG_ENDED");
    v.setVisibility(View.VISIBLE); //<--- add this line
    // Do nothing
    break;

---

编辑

您可以尝试的另一件事是在您的OnTouchListener 中将视图设置为可见状态。试试这个：

img.setOnTouchListener(new View.OnTouchListener() {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        if (event.getAction() == MotionEvent.ACTION_DOWN) {
            ClipData data = ClipData.newPlainText("", "");
            View.DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(img);

            img.startDrag(data, shadowBuilder, img, 0);
            img.setVisibility(View.INVISIBLE);
            return true;
        }

        //ADD THIS SECTION ///////////////////////////////////
        else if(event.getAction() == MotionEvent.ACTION_UP) {
            img.setVisibility(View.VISIBLE);
        }
        //////////////////////////////////////////////////////



        else 
        {
            return false;
        }
    }
});