Android客户端的图形化拖放操作的设计实现

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boolean android.view.View.startDrag(
ClipData data, DragShadowBuilder shadowBuilder, Object myLocalState, int flags)

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/**
* Added in API level 11
* Create a new clip.
* Parameters
* label  Label to show to the user describing this clip.
* mimeTypes  An array of MIME types this data is available as.
* item  The contents of the first item in the clip.
*/
public ClipData (CharSequence label, String[] mimeTypes, ClipData.Item item)

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/**
* The types than an individual item can currently contain are:
* Text: a basic string of text. This is actually a CharSequence, so it can be formatted text supported
* by corresponding Android built-in style spans. (Custom application spans are not supported and will be
* stripped when transporting through the clipboard.)
* Intent: an arbitrary Intent object. A typical use is the shortcut to create when pasting a clipped item
* on to the home screen.
* Uri: a URI reference. This may be any URI (such as an http: URI representing a bookmark),
* however it is often a content: URI. Using content provider references as clips like this allows
* an application to share complex or large clips through the standard content provider facilities.
*/
android.content.ClipData.Item

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/**
* Create an Item consisting of a single block of (possibly styled) text.
*/
public Item(CharSequence text) {
}

/**
* Create an Item consisting of a single block of (possibly styled) text,
* with an alternative HTML formatted representation.  You must
* supply a plain text representation in addition to HTML text; coercion
* will not be done from HTML formated text into plain text.
*/
public Item(CharSequence text, String htmlText) {
}

/**
* Create an Item consisting of an arbitrary Intent.
*/
public Item(Intent intent) {
}

/**
* Create an Item consisting of an arbitrary URI.
*/
public Item(Uri uri) {
}

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/**
* Added in API level 11
* Constructs a shadow image builder based on a View. By default, the resulting drag shadow will have the same appearance and
* dimensions as the View, with the touch point over the center of the View.
* Parameters
* view  A View. Any View in scope can be used.
*/
public View.DragShadowBuilder (View view)

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//给要被拖拽的View mNote_1添加长按事件
mNote_1.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
//在我的代码实现中，给mNote_1设置了一个Text作为其Tag，这里取出来用来构造Item
ClipData.Item item = new ClipData.Item((CharSequence)v.getTag());
String[] mimeTypes = {ClipDescription.MIMETYPE_TEXT_PLAIN};
//构造一个drag data
ClipData dragData = new ClipData(v.getTag().toString(), mimeTypes, item);
//构造一个shadow
View.DragShadowBuilder myShadow = new DragShadowBuilder(mNote_1);
//发起拖拽
v.startDrag(dragData, myShadow, null, 0);
return true;
}
});

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/**
* Added in API level 11
* Called when a drag event is dispatched to a view. This allows listeners to get a chance to override base View behavior.
* Parameters
* v  The View that received the drag event.
* event  The DragEvent object for the drag event.
* Returns
* true if the drag event was handled successfully, or false if the drag event was not handled. Note that false will trigger the View to call its onDragEvent() handler.
*/
public abstract boolean onDrag (View v, DragEvent event)

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trashView.setOnDragListener( new OnDragListener(){
@Override
public boolean onDrag(View v,  DragEvent event){
switch(event.getAction())
{
case DragEvent.ACTION_DROP:
Log.d("trash view", "ACTION_DROP event");
ClipData data = event.getClipData();
CharSequence noteName = data.getItemAt(0).getText();
if(noteName.equals(TAG_NOTE_1)) {
mNote_1.setVisibility(View.GONE);
Toast.makeText(MainActivity.this, "Note 1 has been removed.", Toast.LENGTH_SHORT).show();
} else if(noteName.equals(TAG_NOTE_2)) {
Toast.makeText(MainActivity.this, "Note 2 has been removed.", Toast.LENGTH_SHORT).show();
mNote_2.setVisibility(View.GONE);
}
break;
default:
break;
}
return true;
}
});