拖放图像视图

Question

我正在尝试创建拖放图像视图。我使用了与此链接http://www.tutorialspoint.com/android/android_drag_and_drop.htm 中相同的代码。我可以拖动图像，但在放下时，图像视图变得不可见。有人可以帮我吗？

这是我的 java 代码。

package com.example.draganddropbutton;

import android.app.Activity;
import android.content.ClipData;
import android.content.ClipDescription;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.DragEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
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;
                }
            }
        });



    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

这是我的 xml。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.example.edusys.draganddropbutton.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" />

Answer 1

您在开始拖动时将 ImageView img 的可见性设置为 INVISIBLE，因此您需要在拖动结束时将其设置为可见。

所以在你的拖动监听器中添加以下内容：

case DragEvent.ACTION_DROP:
  img.setVisibility(View.VISIBLE);
  break;

编辑： 还要加

case DragEvent.ACTION_DRAG_ENDED:
  img.setVisibility(View.VISIBLE);
  break;

另请注意：

你已经在 img 上设置了拖拽，因此每当你拖出 img 区域时，拖拽会突然结束。考虑在要拖动图像的视图/布局上添加拖动。

希望这会有所帮助！ :)