三、NoteEditor.java文件学习笔记

这部分代码控制编辑Note的活动。

首先看一下布局文件，

<view xmlns:android="http://schemas.android.com/apk/res/android"
    class="com.example.android.notepad.NoteEditor$LinedEditText"
    android:id="@+id/note"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/transparent"
    android:padding="5dp"
    android:scrollbars="vertical"
    android:fadingEdge="vertical"
    android:gravity="top"
    android:textSize="22sp"
    android:capitalize="sentences"
/>

一个自定义的布局文件，class=这一句指明了哪个类控制这个布局文件。

再来看代码的结构：

LineEditText这个类继承了EditText，实现了onDraw方法。

public LinedEditText(Context context, AttributeSet attrs) {
            super(context, attrs);

            mRect = new Rect();
            mPaint = new Paint();
            mPaint.setStyle(Paint.Style.STROKE);
            mPaint.setColor(0x800000FF);

//画笔与画图区域的初始化
        }

        @Override
        protected void onDraw(Canvas canvas) {

//绘制方法的重载
            int count = getLineCount();
            Rect r = mRect;
            Paint paint = mPaint;
            for (int i = 0; i < count; i++) {
                int baseline = getLineBounds(i, r);
                canvas.drawLine(r.left, baseline + 1, r.right, baseline + 1, paint);

//在每一行的下方绘制一条直线
            }
            super.onDraw(canvas);
        }
    }

这儿理解还是不够，以后补充

回过头来看AndroidManifest.xml文件中NoteEditor Activity的配置。

<activity android:name="NoteEditor"
            android:theme="@android:style/Theme.Holo.Light"
            android:screenOrientation="sensor"
            android:configChanges="keyboardHidden|orientation"
        >
            <!-- This filter says that we can view or edit the data of
                 a single note -->
            <intent-filter android:label="@string/resolve_edit">
                <action android:name="android.intent.action.VIEW" />
                <action android:name="android.intent.action.EDIT" />
                <action android:name="com.android.notepad.action.EDIT_NOTE" />
                <category android:name="android.intent.category.DEFAULT" />
                <data android:mimeType="vnd.android.cursor.item/vnd.google.note" />
            </intent-filter>

            <!-- This filter says that we can create a new note inside
                 of a directory of notes.  The INSERT action creates an
                 empty note; the PASTE action initializes a new note from
                 the current contents of the clipboard. -->
            <intent-filter>
                <action android:name="android.intent.action.INSERT" />
                <action android:name="android.intent.action.PASTE" />
                <category android:name="android.intent.category.DEFAULT" />
                <data android:mimeType="vnd.android.cursor.dir/vnd.google.note" />
            </intent-filter>

        </activity>

NoteEditor的action接受的有EDIT,VIEW,EDIT_NOTE,INSERT,PASTE,DEFSULT。

接着看NoteEditor.java。

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        final Intent intent = getIntent();
        final String action = intent.getAction();
        if (Intent.ACTION_EDIT.equals(action)) {
            mState = STATE_EDIT;
            mUri = intent.getData();
        } else if (Intent.ACTION_INSERT.equals(action)
            mState = STATE_INSERT;
            mUri = getContentResolver().insert(intent.getData(), null);
            if (mUri == null) {

                Log.e(TAG, "Failed to insert new note into " + getIntent().getData());

                finish();
                return;
            }
            setResult(RESULT_OK, (new Intent()).setAction(mUri.toString()));
        } else {

            Log.e(TAG, "Unknown action, exiting");
            finish();
            return;
        }

        mCursor = managedQuery(
            mUri,         // The URI that gets multiple notes from the provider.
            PROJECTION,   // A projection that returns the note ID and note content for each note.
            null,         // No "where" clause selection criteria.
            null,         // No "where" clause selection values.
            null          // Use the default sort order (modification date, descending)
        );
        if (Intent.ACTION_PASTE.equals(action)) {
            // Does the paste
            performPaste();
            // Switches the state to EDIT so the title can be modified.
            mState = STATE_EDIT;
        }

        setContentView(R.layout.note_editor);

        mText = (EditText) findViewById(R.id.note);

        if (savedInstanceState != null) {
            mOriginalContent = savedInstanceState.getString(ORIGINAL_CONTENT);
        }
    }

做的无非是根据action参数得到mState，表明要干什么，intent参数获得mUri，查询得到mCursor。

  protected void onResume() {
        super.onResume();

        if (mCursor != null) {
            // Requery in case something changed while paused (such as the title)
            mCursor.requery();

            mCursor.moveToFirst();

            if (mState == STATE_EDIT) {
                int colTitleIndex = mCursor.getColumnIndex(NotePad.Notes.COLUMN_NAME_TITLE);
                String title = mCursor.getString(colTitleIndex);
                Resources res = getResources();
                String text = String.format(res.getString(R.string.title_edit), title);
                setTitle(text);
            } else if (mState == STATE_INSERT) {
                setTitle(getText(R.string.title_create));
            }

            int colNoteIndex = mCursor.getColumnIndex(NotePad.Notes.COLUMN_NAME_NOTE);
            String note = mCursor.getString(colNoteIndex);
            mText.setTextKeepState(note);
            if (mOriginalContent == null) {
                mOriginalContent = note;
            }

        } else {
            setTitle(getText(R.string.error_title));
            mText.setText(getText(R.string.error_message));
        }
    }

设置title及edittext中的文本。

 protected void onSaveInstanceState(Bundle outState) {
        // Save away the original text, so we still have it if the activity
        // needs to be killed while paused.
        outState.putString(ORIGINAL_CONTENT, mOriginalContent);
    }

在活动结束前保存最初文本。

protected void onPause() {
        super.onPause();

       
        if (mCursor != null) {

            String text = mText.getText().toString();
            int length = text.length();
     if (isFinishing() && (length == 0)) {
                setResult(RESULT_CANCELED);
                deleteNote();

                      } else if (mState == STATE_EDIT) {
                updateNote(text, null);
            } else if (mState == STATE_INSERT) {
                updateNote(text, text);
                mState = STATE_EDIT;
          }
        }
    }

onPause函数，一旦活动不再前台，如果取消，就删除修改内容，编辑，就更新内容，插入，的话也是一样

 public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate menu from XML resource
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.editor_options_menu, menu);

        // Only add extra menu items for a saved note 
        if (mState == STATE_EDIT) {
           
            Intent intent = new Intent(null, mUri);
            intent.addCategory(Intent.CATEGORY_ALTERNATIVE);
            menu.addIntentOptions(Menu.CATEGORY_ALTERNATIVE, 0, 0,
                    new ComponentName(this, NoteEditor.class), null, intent, 0, null);
        }

        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // Check if note has changed and enable/disable the revert option
        int colNoteIndex = mCursor.getColumnIndex(NotePad.Notes.COLUMN_NAME_NOTE);
        String savedNote = mCursor.getString(colNoteIndex);
        String currentNote = mText.getText().toString();
        if (savedNote.equals(currentNote)) {
            menu.findItem(R.id.menu_revert).setVisible(false);
        } else {
            menu.findItem(R.id.menu_revert).setVisible(true);
        }
        return super.onPrepareOptionsMenu(menu);
    }

上面的代码是右键菜单的代码，来看第一个函数是显示editor_options_menue中的内容为菜单内容，第二个根据内容是否改变决定revert菜单项是否显示。

  public boolean onOptionsItemSelected(MenuItem item) {
        // Handle all of the possible menu actions.
        switch (item.getItemId()) {
        case R.id.menu_save:
            String text = mText.getText().toString();
            updateNote(text, null);
            finish();
            break;
        case R.id.menu_delete:
            deleteNote();
            finish();
            break;
        case R.id.menu_revert:
            cancelNote();
            break;
        }
        return super.onOptionsItemSelected(item);
    }

菜单项的交互。

 private final void performPaste() {

       
        ClipboardManager clipboard = (ClipboardManager)
                getSystemService(Context.CLIPBOARD_SERVICE);
 ContentResolver cr = getContentResolver();

        ClipData clip = clipboard.getPrimaryClip();
        if (clip != null) {

            String text=null;
            String title=null;

            ClipData.Item item = clip.getItemAt(0);

            Uri uri = item.getUri();

            if (uri != null && NotePad.Notes.CONTENT_ITEM_TYPE.equals(cr.getType(uri))) {

                // The clipboard holds a reference to data with a note MIME type. This copies it.
                Cursor orig = cr.query(
                        uri,            // URI for the content provider
                        PROJECTION,     // Get the columns referred to in the projection
                        null,           // No selection variables
                        null,           // No selection variables, so no criteria are needed
                        null            // Use the default sort order
                );

                // If the Cursor is not null, and it contains at least one record
                // (moveToFirst() returns true), then this gets the note data from it.
                if (orig != null) {
                    if (orig.moveToFirst()) {
                        int colNoteIndex = mCursor.getColumnIndex(NotePad.Notes.COLUMN_NAME_NOTE);
                        int colTitleIndex = mCursor.getColumnIndex(NotePad.Notes.COLUMN_NAME_TITLE);
                        text = orig.getString(colNoteIndex);
                        title = orig.getString(colTitleIndex);
                    }

                    // Closes the cursor.
                    orig.close();
                }
            }

            // If the contents of the clipboard wasn't a reference to a note, then
            // this converts whatever it is to text.
            if (text == null) {
                text = item.coerceToText(this).toString();
            }

            // Updates the current note with the retrieved title and text.
            updateNote(text, title);
        }
    }

这个是剪切操作的实现，如果剪切的是Note，就查询，获取text,tilte，如果文本，直接作为text，然后调用updateNote()函数保存更改。

private final void updateNote(String text, String title) {


        // Sets up a map to contain values to be updated in the provider.
        ContentValues values = new ContentValues();
        values.put(NotePad.Notes.COLUMN_NAME_MODIFICATION_DATE, System.currentTimeMillis());


        // If the action is to insert a new note, this creates an initial title for it.
        if (mState == STATE_INSERT) {


            // If no title was provided as an argument, create one from the note text.
            if (title == null) {
  
                // Get the note's length
                int length = text.length();

                title = text.substring(0, Math.min(30, length));
                if (length > 30) {
                    int lastSpace = title.lastIndexOf(' ');
                    if (lastSpace > 0) {
                        title = title.substring(0, lastSpace);
                    }
                }
            }
            // In the values map, sets the value of the title
            values.put(NotePad.Notes.COLUMN_NAME_TITLE, title);
        } else if (title != null) {
            // In the values map, sets the value of the title
            values.put(NotePad.Notes.COLUMN_NAME_TITLE, title);
        }


        // This puts the desired notes text into the map.
        values.put(NotePad.Notes.COLUMN_NAME_NOTE, text);
        getContentResolver().update(
                mUri,    // The URI for the record to update.
                values,  // The map of column names and new values to apply to them.
                null,    // No selection criteria are used, so no where columns are necessary.
                null     // No where columns are used, so no where arguments are necessary.
            );
    }

updateNote这个函数，如果title存在，将text,title存入，否则取前30字符为title。

    private final void cancelNote() {
        if (mCursor != null) {
            if (mState == STATE_EDIT) {
                // Put the original note text back into the database
                mCursor.close();
                mCursor = null;
                ContentValues values = new ContentValues();
                values.put(NotePad.Notes.COLUMN_NAME_NOTE, mOriginalContent);
                getContentResolver().update(mUri, values, null, null);
            } else if (mState == STATE_INSERT) {
                // We inserted an empty note, make sure to delete it
                deleteNote();
            }
        }
        setResult(RESULT_CANCELED);
        finish();
    }

    /**
     * Take care of deleting a note.  Simply deletes the entry.
     */
    private final void deleteNote() {
        if (mCursor != null) {
            mCursor.close();
            mCursor = null;
            getContentResolver().delete(mUri, null, null);
            mText.setText("");
        }
    }
}

cancleNote如果取消，就将mOrigContent存回去。

deleteNote删除一条note，将EditText设为空白行。