Android example source code file (InternalSelectionView.java)

This example Android source code file (InternalSelectionView.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, attributeset, content, drawing, graphics, integer, internalselectionview, keyevent, override, paint, rect, string, ui, view

The InternalSelectionView.java Android example source code

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.view;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.view.View;



/**
 * A view that has a known number of selectable rows, and maintains a notion of which
 * row is selected. The rows take up the
 * entire width of the view.  The height of the view is divided evenly among
 * the rows.
 *
 * Notice what this view does to be a good citizen w.r.t its internal selection:
 * 1) calls {@link View#requestRectangleOnScreen} each time the selection changes due to
 *    internal navigation.
 * 2) overrides {@link View#getFocusedRect} by filling in the rectangle of the currently
 *    selected row
 * 3) overrides {@link View#onFocusChanged} and sets selection appropriately according to
 *    the previously focused rectangle.
 */
public class InternalSelectionView extends View {

    private Paint mPainter = new Paint();
    private Paint mTextPaint = new Paint();
    private Rect mTempRect = new Rect();

    private int mNumRows = 5;
    private int mSelectedRow = 0;
    private final int mEstimatedPixelHeight = 10;

    private Integer mDesiredHeight = null;
    private String mLabel = null;


    public InternalSelectionView(Context context, int numRows) {
        this(context, numRows, "");
    }
    
    public InternalSelectionView(Context context, int numRows, String label) {
        super(context);
        mNumRows = numRows;
        mLabel = label;
        init();
    }

    public InternalSelectionView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        setFocusable(true);
        mTextPaint.setAntiAlias(true);
        mTextPaint.setTextSize(10);
        mTextPaint.setColor(Color.WHITE);
    }

    public int getNumRows() {
        return mNumRows;
    }

    public int getSelectedRow() {
        return mSelectedRow;
    }

    public void setDesiredHeight(int desiredHeight) {
        mDesiredHeight = desiredHeight;
    }

    public String getLabel() {
        return mLabel;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(
            measureWidth(widthMeasureSpec),
            measureHeight(heightMeasureSpec));
    }

    private int measureWidth(int measureSpec) {
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        int desiredWidth = 300 + getPaddingLeft() + getPaddingRight();
        if (specMode == MeasureSpec.EXACTLY) {
            // We were told how big to be
            return specSize;
        } else if (specMode == MeasureSpec.AT_MOST) {
            return desiredWidth < specSize ? desiredWidth : specSize;
        } else {
            return desiredWidth;
        }
    }

    private int measureHeight(int measureSpec) {
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        int desiredHeight = mDesiredHeight != null ?
                mDesiredHeight :
                mNumRows * mEstimatedPixelHeight + getPaddingTop() + getPaddingBottom();
        if (specMode == MeasureSpec.EXACTLY) {
            // We were told how big to be
            return specSize;
        } else if (specMode == MeasureSpec.AT_MOST) {
            return desiredHeight < specSize ? desiredHeight : specSize;
        } else {
            return desiredHeight;
        }
    }


    @Override
    protected void onDraw(Canvas canvas) {

        int rowHeight = getRowHeight();

        int rectTop = getPaddingTop();
        int rectLeft = getPaddingLeft();
        int rectRight = getWidth() - getPaddingRight();
        for (int i = 0; i < mNumRows; i++) {

            mPainter.setColor(Color.BLACK);
            mPainter.setAlpha(0x20);

            // draw background rect
            mTempRect.set(rectLeft, rectTop, rectRight, rectTop + rowHeight);
            canvas.drawRect(mTempRect, mPainter);

            // draw forground rect
            if (i == mSelectedRow && hasFocus()) {
                mPainter.setColor(Color.RED);
                mPainter.setAlpha(0xF0);
                mTextPaint.setAlpha(0xFF);
            } else {
                mPainter.setColor(Color.BLACK);
                mPainter.setAlpha(0x40);
                mTextPaint.setAlpha(0xF0);
            }
            mTempRect.set(rectLeft + 2, rectTop + 2,
                    rectRight - 2, rectTop + rowHeight - 2);
            canvas.drawRect(mTempRect, mPainter);

            // draw text to help when visually inspecting
            canvas.drawText(
                    Integer.toString(i),
                    rectLeft + 2,
                    rectTop + 2 - (int) mTextPaint.ascent(),
                    mTextPaint);

            rectTop += rowHeight;
        }
    }

    private int getRowHeight() {
        return (getHeight() - getPaddingTop() - getPaddingBottom()) / mNumRows;
    }

    public void getRectForRow(Rect rect, int row) {
        final int rowHeight = getRowHeight();
        final int top = getPaddingTop() + row * rowHeight;
        rect.set(getPaddingLeft(),
                top,
                getWidth() - getPaddingRight(),
                top + rowHeight);
    }


    void ensureRectVisible() {
        getRectForRow(mTempRect, mSelectedRow);
        requestRectangleOnScreen(mTempRect);
    }


    /* (non-Javadoc)
    * @see android.view.KeyEvent.Callback#onKeyDown(int, android.view.KeyEvent)
    */
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        switch(event.getKeyCode()) {
            case KeyEvent.KEYCODE_DPAD_UP:
                if (mSelectedRow > 0) {
                    mSelectedRow--;
                    invalidate();
                    ensureRectVisible();
                    return true;
                }
                break;
            case KeyEvent.KEYCODE_DPAD_DOWN:
                if (mSelectedRow < (mNumRows - 1)) {
                    mSelectedRow++;
                    invalidate();
                    ensureRectVisible();
                    return true;
                }
                break;
        }
        return false;
    }


    @Override
    public void getFocusedRect(Rect r) {
        getRectForRow(r, mSelectedRow);
    }

    @Override
    protected void onFocusChanged(boolean focused, int direction,
            Rect previouslyFocusedRect) {
        super.onFocusChanged(focused, direction, previouslyFocusedRect);

        if (focused) {
            switch (direction) {
                case View.FOCUS_DOWN:
                    mSelectedRow = 0;
                    break;
                case View.FOCUS_UP:
                    mSelectedRow = mNumRows - 1;
                    break;
                case View.FOCUS_LEFT:  // fall through
                case View.FOCUS_RIGHT:
                    // set the row that is closest to the rect
                    if (previouslyFocusedRect != null) {
                        int y = previouslyFocusedRect.top
                                + (previouslyFocusedRect.height() / 2);
                        int yPerRow = getHeight() / mNumRows;
                        mSelectedRow = y / yPerRow;
                    } else {
                        mSelectedRow = 0;
                    }
                    break;
                default:
                    // can't gleam any useful information about what internal
                    // selection should be...
                    return;
            }
            invalidate();
        }
    }

    @Override
    public String toString() {
        if (mLabel != null) {
            return mLabel;
        }
        return super.toString();
    }
}