51CT0不支持MarkDown，原文請至：簡書
關鍵字： ContextMenu
##背景
我們經常在列表的頁面中，點擊列表中的行，一般進入詳情頁面，長按列表中一行，會彈出一個菜單，包含了對某一行的操作（編輯、刪除等等），也知道通常的用法：
- 0x01. 在Activity中註冊需要上下文菜單的View：
`registerForContextMenu(mListView);`
- 0x02. 然後在Activity中繼承onCreateContextMenu方法，添加菜單項：
```
@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
Log.d(LOG_TAG, "onCreateContextMenu");
super.onCreateContextMenu(menu, v, menuInfo);
menu.setHeaderTitle(R.string.prompt);
menu.add(Menu.NONE, R.id.context_menu_item_delete_record, Menu.NONE, R.string.delete_record);//groupId, itemId, order, title
menu.add(Menu.NONE, R.id.context_menu_item_delete_record_with_file, Menu.NONE, R.string.delete_record_with_file);
}```
**PS：每次長按出現上下文菜單都會調用這個方法**
```
/** * Called when a context menu for the {@code view} is about to
be shown. * Unlike {@link #onCreateOptionsMenu(Menu)}, this will
be called every * time the context menu is about to be shown and
should be populated for * the view (or item inside the view for {@link
AdapterView} subclasses, * this can be found in the {@code
menuInfo})). * <p> * Use {@link #onContextItemSelected(android.view.MenuItem)} to know when an
* item has been selected. * <p> * It is not safe to hold onto the
context menu after this method returns. * */
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {
}
```
- 0x03. 接下來長按列表中一行的時候，會彈出上下文菜單：
- 0x04. 點擊菜單後，在Activity中繼承onContextItemSelected方法進行處理：
```
@Override
public boolean onContextItemSelected(MenuItem item) {
switch (item.getItemId()){
}
}
```
- 0x05. 獲取Item標識（id）
我們刪除數據庫或者一行記錄的時候，要知道主鍵（一般是id）才能進行操作，很多人就想辦法，有的是把ListView的每個ItemView添加一個LongClickListener，然後長按的時候記錄下Position，然後在進行相應處理。
其實有更優雅的做法，onContextItemSelected(MenuItem item)回調的參數item可以獲取item.getMenuInfo()，在ListView和Adapter的模式中，可以強制轉換成AdapterContextMenuInfo，拿到targetView（即所長按行的ItemVew，如果我們需要什麼參數，直接放到View.setTag中去即可）：
```
AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();
int index = info.position;
View view = info.targetView;
```
至此，常見的用法就完了，那麼遇到其他自定義View呢？
- 0x06. 自定義View的ContextMenu實現
下面以用到的RecycleView爲例，沒有了ListView及其Adapter的封裝，我們需要自己處理ContextMenu。
最重要的是繼承View的兩個方法：
1.上下文菜單Item的附加信息（上面item.getMenuInfo()）；
```
/** * Views should implement this if they have extra information to
associate * with the context menu. The return result is supplied as a
parameter to * the {@link
OnCreateContextMenuListener#onCreateContextMenu(ContextMenu,
View, ContextMenuInfo)} * callback. * * @return Extra information
about the item for which the context menu * should be shown.
This information will vary across different * subclasses of View. */
protected ContextMenuInfo getContextMenuInfo() {
return null;
}
```
2.ViewGroup的showContextMenuForChild，每次彈出上下文菜單都會調用此方法，需要在這裏更新ContextMenuInfo；
```
/** * {@inheritDoc} */
public boolean showContextMenuForChild(View originalView) {
return mParent != null && mParent.showContextMenuForChild(originalView);
}
```
- 0x07. 自定義RecycleView的ContextMenu全部代碼
```
package com.lbrant.phone.view;
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.Log;
import android.view.ContextMenu;
import android.view.View;
/**
* 作者：dell
* 時間：2015/11/3 18:34
* 文件：PhoneRecorder
* 描述：
*/
public class ContextMenuRecyclerView extends RecyclerView {
private static final String LOG_TAG = "ContextMenuRecyclerView";
private RecyclerContextMenuInfo mContextMenuInfo = new RecyclerContextMenuInfo();
public ContextMenuRecyclerView(Context context) {
super(context);
}
public ContextMenuRecyclerView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public ContextMenuRecyclerView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
@Override
protected ContextMenu.ContextMenuInfo getContextMenuInfo() {
return mContextMenuInfo;
}
@Override
public boolean showContextMenuForChild(View originalView) {
Log.d(LOG_TAG, "showContextMenuForChild");
Object tag = originalView.getTag();
if (tag instanceof RecyclerItemMarker) {
mContextMenuInfo.mRecycleItemMarker = (RecyclerItemMarker) tag;
}
return super.showContextMenuForChild(originalView);
}
public static class RecyclerItemMarker {
public final int position;
public final Object obj;
public RecyclerItemMarker(int position, Object obj) {
this.position = position;
this.obj = obj;
}
}
public static class RecyclerContextMenuInfo implements ContextMenu.ContextMenuInfo {
public RecyclerItemMarker mRecycleItemMarker;
}
}
private class RecordRecycleViewAdapter extends RecyclerView.Adapter<RecordRecycleViewAdapter.RecordViewHolder> {
private Cursor mCallRecordCursor;
private int mIdIndex;
private int mPhoneNumberIndex;
private int mCallTimeIndex;
private int mDurationIndex;
private int mPathIndex;
public RecordRecycleViewAdapter(Cursor cursor) {
mCallRecordCursor = cursor;
updateCursorColumnIndex();
}
private void updateCursorColumnIndex() {
if (mCallRecordCursor != null) {
mIdIndex = mCallRecordCursor.getColumnIndex(BaseDatabaseHelper.RECORDS_COLUMNS._ID);
mPhoneNumberIndex = mCallRecordCursor.getColumnIndex(BaseDatabaseHelper.RECORDS_COLUMNS.NUMBER);
mCallTimeIndex = mCallRecordCursor.getColumnIndex(BaseDatabaseHelper.RECORDS_COLUMNS.CALL_TIME);
mDurationIndex = mCallRecordCursor.getColumnIndex(BaseDatabaseHelper.RECORDS_COLUMNS.DURATION);
mPathIndex = mCallRecordCursor.getColumnIndex(BaseDatabaseHelper.RECORDS_COLUMNS.PATH);
}
}
@Override
public RecordRecycleViewAdapter.RecordViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View contentView = LayoutInflater.from(parent.getContext()).inflate(R.layout.record_list_item, parent, false);
RecordViewHolder viewHolder = new RecordViewHolder(contentView);
return viewHolder;
}
@Override
public void onBindViewHolder(RecordRecycleViewAdapter.RecordViewHolder holder, final int position) {
holder.itemView.setLongClickable(true);
if (mCallRecordCursor != null && mCallRecordCursor.moveToPosition(position)) {
long id = mCallRecordCursor.getLong(mIdIndex);
String phoneNumber = mCallRecordCursor.getString(mPhoneNumberIndex);
long seconds = mCallRecordCursor.getLong(mDurationIndex);
String callTime = mCallRecordCursor.getString(mCallTimeIndex);
String path = mCallRecordCursor.getString(mPathIndex);
String duration = String.format("%1$02d:%2$02d:%3$02d", seconds / 3600, seconds % 3600 / 60, seconds % 60);
RecordInfo info = new RecordInfo();
info.setId(id);
info.setPhoneNumber(phoneNumber);
info.setSecondsDuration(seconds);
info.setCallTime(callTime);
info.setPath(path);
holder.itemView.setTag(new ContextMenuRecyclerView.RecyclerItemMarker(position, info));
holder.mTextViewPhoneNumber.setText(phoneNumber);
holder.mTextViewDuration.setText(duration);
holder.mTextviewCallTime.setText(callTime);
Cursor cursor = queryContactByPhoneNumber(ContactsContract.CommonDataKinds.Phone.NUMBER + " = '" + phoneNumber + "'");
if (cursor != null) {
if (cursor.moveToNext()) {
long contactId = cursor.getInt(0);
Cursor contactCursor = queryContact(ContactsContract.Contacts._ID + "=" + contactId);
if (contactCursor != null) {
holder.mTextViewName.setText(contactCursor.getString(1));
contactCursor.close();
}
}
cursor.close();
}
}
}
@Override
public void onViewRecycled(RecordViewHolder holder) {
super.onViewRecycled(holder);
holder.itemView.setOnCreateContextMenuListener(null);
}
@Override
public int getItemCount() {
return mCallRecordCursor == null ? 0 : mCallRecordCursor.getCount();
}
public void changeCursor(Cursor cursor) {
if (cursor != mCallRecordCursor) {
if (mCallRecordCursor != null) {
mCallRecordCursor.close();
}
mCallRecordCursor = cursor;
updateCursorColumnIndex();
notifyDataSetChanged();
}
}
public class RecordViewHolder extends RecyclerView.ViewHolder {
private ImageView mImageViewAvatar;
private TextView mTextViewPhoneNumber;
private TextView mTextViewName;
private TextView mTextviewCallTime;
private TextView mTextViewDuration;
public RecordViewHolder(View itemView) {
super(itemView);
mImageViewAvatar = (ImageView) itemView.findViewById(R.id.imageViewAvatar);
mTextViewName = (TextView) itemView.findViewById(R.id.textViewName);
mTextViewPhoneNumber = (TextView) itemView.findViewById(R.id.textViewPhoneNumber);
mTextviewCallTime = (TextView) itemView.findViewById(R.id.textViewCallTime);
mTextViewDuration = (TextView) itemView.findViewById(R.id.textViewDuration);
}
}
}
```
**有兩個地方需要注意：**
1.onBindViewHolder中給ItemView添加Tag;
2.設置ItemView的LongClickable爲true，不然不會出現上下文菜單（具體原因見ContextMenu原理分析）；
holder.itemView.setLongClickable(true);