这里有多个涂鸦应用程序都有一个撤消按钮。我没有实现这些，因为我的代码不同，但我已经看过了这些概念。 I.E存储数组中的点。
当程序检测到触摸事件时：
@Override
public boolean onTouchEvent(MotionEvent event) {
float touchX = event.getX(); //Gets the fingers x position
float touchY = event.getY(); //gets the fingers y position
PointF points = new PointF(); //init a new PointF
points.x = touchX; //store the coordinates in the Point object
points.y = touchY;
_pointList.add(points); //add this to the list of Points (array)
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
_path.moveTo(touchX, touchY); //Set the beginning of the next contour to the point (x,y)
//will start drawing from where the last point was
break;
case MotionEvent.ACTION_MOVE:
_path.lineTo(touchX, touchY);
break;
case MotionEvent.ACTION_UP:
break;
}
invalidate();
return true;
}
理论上，_pointList Array应按顺序捕获所有触摸输入。这很明显，因为控制台显示了阵列的大小。
在onDraw方法中，它应该遍历a _pointList列表中的所有点。由于它包含用户在屏幕上交互的所有点，因此理论上它应该从内存中绘制线条。
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (PointF points : _pointList) {
_path.moveTo(points.x, points.y);
_path.lineTo(points.x, points.y);
_canvas.drawPath(_path, _paint);
}
canvas.drawBitmap(_bitmap, 0, 0, _paint);
}
当应用程序运行时，我可以在屏幕上绘图，并且由于清除方法，屏幕会清除。
public void clear(){
_pointList.clear();// empty the list that stores the points
_bitmap = Bitmap.createBitmap(1000,1000,
Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
_path = new Path();
_paint = new Paint(Paint.DITHER_FLAG);
//Added later..
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
//empties the screen
invalidate();
}
但是，在我的撤销方法中，它应该从_pointList列表中删除其中一个点（包含用户X和Y触摸输入）。删除该点后，屏幕应重新绘制内存中的所有行。
public void undo() {
Log.d("Number", "undo:" + _pointList.size() );
if (_pointList.size()>0){
_bitmap = Bitmap.createBitmap(1000,1000,
Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
_path = new Path();
_paint = new Paint(Paint.DITHER_FLAG);
//Added later..
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
_pointList.remove(_pointList.size() - 1);
invalidate();
}
}
此方法与＆＃39; clear＆＃39;具有相同的效果。方法，不重绘行，
我撤消按钮的其他替代方法是将位图放入数组中，但我确信这会导致内存问题，因为它是一个动态程序。
问题：为什么＆＃39;无效＆＃39;来自＆＃39;撤消＆＃39;方法更新屏幕？
更新
整个代码：
- 画图 -
package com.example.moynul.myapplication;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Point;
import android.graphics.PointF;
import android.graphics.PorterDuff;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
* Created by moynu on 10/12/2015.
*/
public class Draw extends View {
private Paint _paint = new Paint();
private Path _path = new Path();
private Bitmap _bitmap;
private Canvas _canvas;
private List<PointF> _pointList = new ArrayList<PointF>();
public Draw(Context context) {
super(context);
init(null, 0);
}
public Draw(Context context, AttributeSet attrs) {
super(context, attrs);
init(attrs,0);
}
public Draw(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init(attrs, defStyleAttr);
}
private void init(AttributeSet attrs, int defStyleAttr) {
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
_bitmap = Bitmap.createBitmap (1080, 1920, Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float touchX = event.getX(); //Gets the fingers x position
float touchY = event.getY(); //gets the fingers y position
PointF points = new PointF(); //init a new PointF
points.x = touchX; //store the coordinates in the Point object
points.y = touchY;
_pointList.add(points); //add this to the list of Points (array)
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
_path.moveTo(touchX, touchY); //Set the beginning of the next contour to the point (x,y)
//will start drawing from where the last point was
break;
case MotionEvent.ACTION_MOVE:
_path.lineTo(touchX, touchY);
break;
case MotionEvent.ACTION_UP:
break;
}
invalidate();
return true;
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (PointF points : _pointList) {
_path.moveTo(points.x, points.y);
_path.lineTo(points.x, points.y);
_canvas.drawPath(_path, _paint);
}
canvas.drawBitmap(_bitmap, 0, 0, _paint);
}
public void clear(){
_pointList.clear();// empty the list that stores the points
_bitmap = Bitmap.createBitmap(1000,1000,
Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
_path = new Path();
_paint = new Paint(Paint.DITHER_FLAG);
//Added later..
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
//empties the screen
invalidate();
}
public void undo() {
Log.d("Number", "undo:" + _pointList.size());
if (_pointList.size()>0){
_pointList.remove(_pointList.size() - 1);
_bitmap = Bitmap.createBitmap(1000,1000,
Bitmap.Config.ARGB_8888);
_canvas = new Canvas(_bitmap);
_path = new Path();
_paint = new Paint(Paint.DITHER_FLAG);
//Added later..
_paint.setColor(Color.RED);
_paint.setAntiAlias(true);
_paint.setStyle(Paint.Style.STROKE);
invalidate();
}
}
}
答案 0 :(得分：0)
在onDraw（）for for循环
中更改canvas.drawPath(_path, _paint);
希望它能运作
答案 1 :(得分：0)
您的onDraw方法存在问题，您始终在路径上的相同位置（0,0）上绘制_bitmap。将我的代码替换为您的onDraw代码：
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (PointF points : _pointList) {
_path.moveTo(points.x, points.y);
_path.lineTo(points.x, points.y);
_canvas.drawPath(_path, _paint);
canvas.drawBitmap(_bitmap, points.x, points.y, _paint);
}
}