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Android开发:拖拽

google官网的training和API两个地方都提到了拖拽的实现,两种方法不太一样。

方法一

training(https://developer.android.com/training/gestures/scale.html)中提到的方法是监听onTouchEvent,在ACTION_DOWN的时候记录位置,在ACTION_MOVE的时候获取坐标,改变拖拽的控件位置。

方法二

在android3.0及以上可以使用View.OnDragListener。

下面是我写的简单的demo:

activity_drag_demo.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/activity_drag_demo"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.topsports.testapplication.DragDemoActivity">
<ImageView
    android:id="@+id/imageView"
    android:layout_width="100dp"
    android:layout_height="100dp"
    android:background="@drawable/c1"/>

    <FrameLayout
        android:background="#c7f6ff"
        android:layout_width="500dp"
        android:layout_height="500dp"
        android:id="@+id/content_fragment"
        android:layout_alignParentBottom="true"></FrameLayout>

    <FrameLayout
        android:background="#dce9c1"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:id="@+id/content_fragment2"
        android:layout_alignParentRight="true"
        android:layout_alignParentBottom="true"></FrameLayout>


</RelativeLayout>
在官网示例基础上修改的DragDemoActivity:package com.topsports.testapplication;
import android.content.ClipData;
import android.content.ClipDescription;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Point;
import android.graphics.drawable.ColorDrawable;
import android.graphics.drawable.Drawable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.DragEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.Toast;

public class DragDemoActivity extends AppCompatActivity {

    private ImageView imageView;

    private FrameLayout frameLayout;
    private FrameLayout frameLayout2;

    private static final String IMAGEVIEW_TAG = "icon bitmap";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_drag_demo);

        imageView=(ImageView)findViewById(R.id.imageView);
        frameLayout=(FrameLayout)findViewById(R.id.content_fragment);
        frameLayout2=(FrameLayout)findViewById(R.id.content_fragment2);

        imageView.setTag(IMAGEVIEW_TAG);

        imageView.setOnLongClickListener(new View.OnLongClickListener() {

             public boolean onLongClick(View v) {

                 v.getBackground().setAlpha(100);

                 ClipData.Item item = new ClipData.Item(v.getTag().toString());

ClipData dragData = http://www.mamicode.com/new ClipData(v.getTag().toString(),new String[]{ClipDescription.MIMETYPE_TEXT_PLAIN},item); // Instantiates the drag shadow builder. View.DragShadowBuilder myShadow = new View.DragShadowBuilder(v); v.startDrag(dragData, // the data to be dragged myShadow, // the drag shadow builder null, // no need to use local data 0 // flags (not currently used, set to 0) ); return true; } }); frameLayout.setOnDragListener(new myDragEventListener()); frameLayout2.setOnDragListener(new myDragEventListener()); imageView.setOnDragListener(new myDragEventListener()); }protected class myDragEventListener implements View.OnDragListener { // This is the method that the system calls when it dispatches a drag event to the // listener. public boolean onDrag(View v, DragEvent event) { // Defines a variable to store the action type for the incoming event final int action = event.getAction(); // Handles each of the expected events switch(action) { case DragEvent.ACTION_DRAG_STARTED: // Determines if this View can accept the dragged data if (event.getClipDescription().hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN)) { v.invalidate(); // returns true to indicate that the View can accept the dragged data. return true; } // Returns false. During the current drag and drop operation, this View will // not receive events again until ACTION_DRAG_ENDED is sent. return false; case DragEvent.ACTION_DRAG_ENTERED: // Applies a green tint to the View. Return true; the return value is ignored // Invalidate the view to force a redraw in the new tint v.invalidate(); return true; case DragEvent.ACTION_DRAG_LOCATION: // Ignore the event return true; case DragEvent.ACTION_DRAG_EXITED: // Re-sets the color tint to blue. Returns true; the return value is ignored. // Invalidate the view to force a redraw in the new tint v.invalidate(); return true; case DragEvent.ACTION_DROP: // Gets the item containing the dragged data ClipData.Item item = event.getClipData().getItemAt(0); // Gets the text data from the item. String dragData =http://www.mamicode.com/ item.getText().toString(); // Displays a message containing the dragged data. Toast.makeText(DragDemoActivity.this, "Dragged data is " + dragData, Toast.LENGTH_LONG).show(); // Turns off any color tints if(v instanceof FrameLayout){ ((ViewGroup)imageView.getParent()).removeView(imageView); ((FrameLayout)v).addView(imageView); } // Invalidates the view to force a redraw v.invalidate(); // Returns true. DragEvent.getResult() will return true. return true; case DragEvent.ACTION_DRAG_ENDED: // Turns off any color tinting // Invalidates the view to force a redraw v.invalidate(); // Does a getResult(), and displays what happened. if (event.getResult()) { Toast.makeText(DragDemoActivity.this, "The drop was handled.", Toast.LENGTH_LONG).show(); } else { Toast.makeText(DragDemoActivity.this, "The drop didn‘t work.", Toast.LENGTH_LONG).show(); } imageView.getBackground().setAlpha(255); // returns true; the value is ignored. return true; // An unknown action type was received. default: Log.e("DragDrop Example","Unknown action type received by OnDragListener."); break; } return false; } } }

实现的是将图片拖进两个layout中,并在两个layout间来回拖动。

代码做简单的解释

在长按imageview的时候开始拖拽事件

 

ClipData.Item item = new ClipData.Item(v.getTag().toString());

ClipData dragData = http://www.mamicode.com/new ClipData(v.getTag().toString(),new String[]{ClipDescription.MIMETYPE_TEXT_PLAIN},item);

这两句是为拖动的view创建传递的数据(可以省略)

 

View.DragShadowBuilder myShadow = new View.DragShadowBuilder(v)

这句根据imageview(v)创建一个拖拽的阴影,就像在桌面上拖动应用图标一样,产生一个view的图像副本,产生拖动效果。

 

frameLayout.setOnDragListener(new myDragEventListener());

frameLayout2.setOnDragListener(new myDragEventListener());

imageView.setOnDragListener(new myDragEventListener());

设置拖拽的事件监听(拖动的对象和被放置的对象)实现View.OnDragListener的onDrag方法,判断event.getAction()的值进行不同的操作。

 

Android开发:拖拽