如何创建自定义拖动阴影？

Question

我想要实现的目标:

我想在Android中创建拖放功能.我想使用特定的布局(与拖动的对象本身不同)作为拖动阴影.

我得到了什么结果:

我的方法都没有按预期工作 - 我最终没有可见的拖动阴影(虽然目标确实接收到了掉落).

我尝试了什么:

我试过了

• drag_item在活动中展开布局,然后将其作为参数传递给阴影构建器的构造函数

和

• drag_item在阴影生成器的onDrawShadow方法中膨胀布局,然后在其上绘制canvas

布局:

我的活动布局:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:tools="http://schemas.android.com/tools"
              android:id="@+id/container"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              tools:context="com.example.app.DragDropTestActivity"
              tools:ignore="MergeRootFrame">
    <TextView
        android:id="@+id/tvReceiver"
        android:text="Drop here"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <Button
        android:id="@+id/btnDragged"
        android:layout_height="wrap_content"
        android:text="Drag me"
        android:layout_width="match_parent"/>
</LinearLayout>

我想用作拖动阴影的布局:

dragged_item.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="match_parent"
              android:layout_height="match_parent">
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Dragged Item"/>
</LinearLayout>

源代码:

下面是用两种方法的代码(由下式表示1,BuilderOne并且2,BuilderTwo分别为):

package com.example.app;

import android.graphics.Canvas;
import android.graphics.Point;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;

public class DragDropTestActivity extends ActionBarActivity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_drag_drop_test);
        Button dragged = (Button) findViewById(R.id.btnDragged);

        dragged.setOnTouchListener(
            new View.OnTouchListener()
            {
                @Override
                public boolean onTouch(View v, MotionEvent event)
                {
                    if (event.getAction() != MotionEvent.ACTION_DOWN) {
                        return false;
                    }
                    LayoutInflater inflater = getLayoutInflater();

                    int approach = 1;    
                    // both approaches fail
                    switch (approach) {
                        case 1: {
                            View draggedItem = inflater.inflate(R.layout.dragged_item, null);
                            BuilderOne builder = new BuilderOne(draggedItem);
                            v.startDrag(null, builder, null, 0);
                            break;
                        }
                        case 2: {
                            BuilderTwo builder = new BuilderTwo(inflater, v);
                            v.startDrag(null, builder, null, 0);
                            break;
                        }
                    }

                    return true;
                }
            });
    }

我的BuilderOne班级:

    public static class BuilderOne extends View.DragShadowBuilder
    {
        public BuilderOne(View view)
        {
            super(view);
        }

        @Override
        public void onProvideShadowMetrics(Point shadowSize, Point shadowTouchPoint)
        {
            super.onProvideShadowMetrics(
                shadowSize,
                shadowTouchPoint);
        }
    }

和BuilderTwo班级:

    public static class BuilderTwo extends View.DragShadowBuilder
    {
        final LayoutInflater inflater;

        public BuilderTwo(LayoutInflater inflater, View view)
        {
            super(view);
            this.inflater = inflater;
        }

        @Override
        public void onProvideShadowMetrics(Point shadowSize, Point shadowTouchPoint)
        {
            super.onProvideShadowMetrics(
                shadowSize,
                shadowTouchPoint);
        }

        @Override
        public void onDrawShadow(Canvas canvas)
        {
            final View draggedItem = inflater.inflate(R.layout.dragged_item, null);
            if (draggedItem != null) {
                draggedItem.draw(canvas);
            }
        }
    }
}

题:

我做错了什么？

更新:

赏金补充道.

Answer 1

简单来说，你只需要这个：

private final class TouchListener implements View.OnTouchListener {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        if (event.getActionMasked() == MotionEvent.ACTION_DOWN) {
            v.startDrag(ClipData.newPlainText("", ""), new View.DragShadowBuilder(v), v, 0);
        }
        return true;
    }
}

（您不一定需要 BuilderOne 和 BuilderTwo 类）