我需要从MainActivity类调用invalidate（）方法。我可以从我的CanvasView类中调用它，但是从MainActivity，它给了我一个错误。说无效是非静态方法。我如何通过这个？我已经搜索并尝试了一些解决方案，但还没有开始工作。
我想从屏幕上删除绘制的项目，但是当我从菜单列表中选择“撤消”时，它不会更新屏幕。只有当我触摸屏幕时，才会显示Undos元素。
我的CanvasView类
package com.example.HW3;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Point;
import android.graphics.Rect;
import android.os.Handler;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
/**
* Android Kimp.
* @author Martin
*
*/
public class CanvasView extends View {
/**
* Rectangles.
*/
private Rect rectangle = new Rect();
/**
* These help calculating rectangle coordinates.
*/
private float d1 = 0, d2 = 0;
/**
* Canvas.
*/
private Canvas canvas = new Canvas();
/**
* Paint to draw shapes.
*/
private Paint paint = new Paint();
/**
* Paint to draw shapes.
*/
private Paint paint2 = new Paint();
/**
* Paint to draw shapes.
*/
private Paint paint3 = new Paint();
/**
* Paint to draw shapes.
*/
private Paint paint4 = new Paint();
/**
* Path.
*/
private Path path = new Path();
/**
* Point.
*/
private Point point = new Point();
/**
* List for lines.
*/
private static List<Path> lines = new ArrayList<Path>();
private static List<Path> lines2 = new ArrayList<Path>();
/**
* List for points.
*/
private static List<Point> points = new ArrayList<Point>();
private static List<Point> points2 = new ArrayList<Point>();
/**
* List for rectangles.
*/
private static List<Rect> rectangles = new ArrayList<Rect>();
private static List<Rect> rectangles2 = new ArrayList<Rect>();
private static List<Integer> elements = new ArrayList<Integer>();
private static List<Integer> elements2 = new ArrayList<Integer>();
/**
* Touch coordinates.
*/
private float x, startX, endX;
/**
* Touch coordinates.
*/
private float y, startY, endY;
/**
* This checks whether user draws a line or a point.
*/
private int whichShape;
private boolean touchStarted = false;
/**
* Enum to hold the value of DrawMode, whether user wants to draw lines or rectangles.
*
*/
public enum undoRedo {
DoUndoRedo, DoNothing
};
public static undoRedo currentState = undoRedo.DoNothing;
public enum DrawMode {
/**
* DrawMode possibilities.
*/
FreeDrawMode, RectDrawMode, SelectAndDrag
};
/**
* Sets current DrawMode, when application starts.
*/
public static DrawMode currentDrawMode = DrawMode.FreeDrawMode;
/**
* Sets DrawMode.
* @param newDrawMode
*/
final Handler handler = new Handler();
/**
* Runnable interface to detect long press.
*/
Runnable mLongPressed = new Runnable() {
public void run() {
for (int i = 0; i < getRectangles().size(); i++) {
Log.i("", "Long press!");
Rect a = getRectangles().get(i);
System.out.println(a + " " + i);
double x = getRectangles().get(i).left;
System.out.println(a + " " + x);
currentDrawMode = DrawMode.SelectAndDrag;
}
}
};
/**
* CanvasView.
* @param context
* @param attrs
*/
public CanvasView(Context context, AttributeSet attrs) {
super(context, attrs);
paint.setAntiAlias(true);
paint.setStrokeWidth(3);
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
paint2.setAntiAlias(true);
paint2.setStrokeWidth(3);
paint2.setColor(Color.RED);
paint2.setStyle(Paint.Style.STROKE);
paint2.setStrokeJoin(Paint.Join.ROUND);
paint3.setAntiAlias(true);
paint3.setColor(Color.BLACK);
paint3.setStrokeWidth(3);
paint3.setStyle(Paint.Style.STROKE);
paint3.setStrokeJoin(Paint.Join.ROUND);
paint4.setAntiAlias(true);
paint4.setColor(Color.BLACK);
paint4.setStrokeWidth(3);
paint4.setStyle(Paint.Style.STROKE);
paint4.setShadowLayer(10,5,5,Color.BLACK);
paint4.setStrokeJoin(Paint.Join.ROUND);
}
@Override
protected void onDraw(Canvas canvas) {
for (Rect r : getRectangles()) {
canvas.drawRect(r, paint);
}
canvas.drawRect(rectangle, paint3);
for (Path p : getLines()) {
canvas.drawPath(p, paint);
}
canvas.drawPath(path, paint2);
for (Point point : getPoints()) {
canvas.drawCircle(point.x, point.y, 1, paint);
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
x = event.getX();
y = event.getY();
if (event.getAction() == MotionEvent.ACTION_DOWN) {
handler.postDelayed(mLongPressed, 500);
}
if ((event.getAction() == MotionEvent.ACTION_MOVE)
|| (event.getAction() == MotionEvent.ACTION_UP)) {
handler.removeCallbacks(mLongPressed);
}
if (currentDrawMode == DrawMode.FreeDrawMode) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
// Set new starting point
paint2.setColor(Color.RED);
path = new Path();
path.moveTo(x, y);
touchStarted = true;
break;
case MotionEvent.ACTION_MOVE:
touchStarted = false;
path.lineTo(x, y);
break;
case MotionEvent.ACTION_UP:
if (touchStarted) {
point = new Point();
point.x = (int) x;
point.y = (int) y;
paint2.setColor(Color.BLACK);
whichShape = 1;
getElements().add(whichShape);
getPoints().add(point);
getElements2().clear();
touchStarted = false;
System.out.println("here");
} else {
System.out.println("there");
paint2.setColor(Color.BLACK);
whichShape = 2;
getElements().add(whichShape);
getLines().add(path);
getElements2().clear();
}
break;
default:
return false;
}
} else if (currentDrawMode == DrawMode.RectDrawMode) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
// Set a new starting point
rectangle = new Rect();
paint3.setColor(Color.RED);
startX = event.getX();
startY = event.getY();
System.out.println("down");
break;
case MotionEvent.ACTION_MOVE:
endX = event.getX();
endY = event.getY();
System.out.println("move");
System.out.println(startX + " " + endX + " " + startY + " " + endY);
if (startX >= endX && startY >= endY) {
rectangle.set((int) endX, (int) endY, (int) startX,
(int) startY);
canvas.drawRect(rectangle, paint2);
} else if (startX >= endX && startY <= endY) {
d1 = startX + (endX - startX);
d2 = startY + (endY - startY);
rectangle.set((int) d1, (int) startY, (int) startX,
(int) d2);
canvas.drawRect(rectangle, paint3);
} else if (startX <= endX && startY >= endY) {
d1 = startY + (endY - startY);
d2 = startX + (endX - startX);
rectangle.set((int) startX, (int) d1, (int) d2,
(int) startY);
canvas.drawRect(rectangle, paint3);
System.out.println("olen siin");
} else {
rectangle.set((int) startX, (int) startY, (int) endX,
(int) endY);
canvas.drawRect(rectangle, paint3);
}
break;
case MotionEvent.ACTION_UP:
System.out.println("up");
paint3.setColor(Color.BLACK);
whichShape = 3;
getElements().add(whichShape);
getRectangles().add(rectangle);
getElements2().clear();
break;
default:
return false;
}
} else if (currentDrawMode == DrawMode.SelectAndDrag) {
switch (event.getAction()) {
case MotionEvent.ACTION_MOVE:
break;
case MotionEvent.ACTION_UP:
break;
default:
return false;
}
}
// Makes our view repaint and call onDraw
invalidate();
return true;
}
public static List<Integer> getElements() {
return elements;
}
public static void setElements(List<Integer> elements) {
CanvasView.elements = elements;
}
public static List<Point> getPoints() {
return points;
}
public static void setPoints(List<Point> points) {
CanvasView.points = points;
}
public static List<Path> getLines() {
return lines;
}
public static void setLines(List<Path> lines) {
CanvasView.lines = lines;
}
public static List<Rect> getRectangles() {
return rectangles;
}
public static void setRectangles(List<Rect> rectangles) {
CanvasView.rectangles = rectangles;
}
public static List<Point> getPoints2() {
return points2;
}
public static void setPoints2(List<Point> points2) {
CanvasView.points2 = points2;
}
public static List<Integer> getElements2() {
return elements2;
}
public static void setElements2(List<Integer> elements2) {
CanvasView.elements2 = elements2;
}
public static List<Path> getLines2() {
return lines2;
}
public static void setLines2(List<Path> lines2) {
CanvasView.lines2 = lines2;
}
public static List<Rect> getRectangles2() {
return rectangles2;
}
public static void setRectangles2(List<Rect> rectangles2) {
CanvasView.rectangles2 = rectangles2;
}
}
我的MainActivity类
package com.example.HW3;
import com.example.HW3.CanvasView.undoRedo;
import com.example.androiddrawing.R;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.Window;
import android.view.WindowManager;
/**
* Android application.
* @author Martin
*
*/
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.default_drawing) {
CanvasView.currentDrawMode = CanvasView.DrawMode.FreeDrawMode;
return true;
} else if (id == R.id.draw_rectangle) {
CanvasView.currentDrawMode = CanvasView.DrawMode.RectDrawMode;
return true;
} else if (id == R.id.undo) {
int listSize = CanvasView.getElements().size();
System.out.println(CanvasView.getElements().size());
if (CanvasView.getElements().size() == 0) {
return true;
} else if (CanvasView.getElements().get(listSize - 1) == 1) {
// I WANT TO CALL INVALIDATE() FROM HERE CanvasView.getPoints2().add(CanvasView.getPoints().get(CanvasView.getPoints().size() - 1));
CanvasView.getElements2().add(1);
CanvasView.getPoints().remove(CanvasView.getPoints().size() - 1);
CanvasView.getElements().remove(CanvasView.getElements().size() - 1);
CanvasView.currentState = CanvasView.undoRedo.DoUndoRedo;
return true;
} else if (CanvasView.getElements().get(listSize - 1) == 2) {
CanvasView.getLines2().add(CanvasView.getLines().get(CanvasView.getLines().size() - 1));
CanvasView.getElements2().add(2);
CanvasView.getLines().remove(CanvasView.getLines().size() - 1);
CanvasView.getElements().remove(CanvasView.getElements().size() - 1);
CanvasView.currentState = CanvasView.undoRedo.DoUndoRedo;
return true;
} else if (CanvasView.getElements().get(listSize - 1) == 3) {
CanvasView.getRectangles2().add(CanvasView.getRectangles2().get(CanvasView.getRectangles2().size() - 1));
CanvasView.getElements2().add(3);
CanvasView.getRectangles().remove(CanvasView.getRectangles().size() - 1);
CanvasView.getElements().remove(CanvasView.getElements().size() - 1);
CanvasView.currentState = CanvasView.undoRedo.DoUndoRedo;
return true;
}
return true;
} else if (id == R.id.redo) {
int listSize2 = CanvasView.getElements2().size();
System.out.println(CanvasView.getElements2().size());
if (CanvasView.getElements2().size() == 0) {
return true;
} else if (CanvasView.getElements2().get(listSize2 - 1) == 1) {
CanvasView.getPoints().add(CanvasView.getPoints2().get(CanvasView.getPoints2().size() - 1));
CanvasView.getPoints2().remove(CanvasView.getPoints2().size() - 1);
CanvasView.getElements2().remove(CanvasView.getElements2().size() - 1);
CanvasView.getElements().add(1);
CanvasView.currentState = CanvasView.undoRedo.DoUndoRedo;
return true;
} else if (CanvasView.getElements2().get(listSize2 - 1) == 2) {
CanvasView.getLines().add(CanvasView.getLines2().get(CanvasView.getLines2().size() - 1));
CanvasView.getLines2().remove(CanvasView.getLines2().size() - 1);
CanvasView.getElements2().remove(CanvasView.getElements().size() - 1);
CanvasView.getElements().add(2);
CanvasView.currentState = CanvasView.undoRedo.DoUndoRedo;
return true;
} else if (CanvasView.getElements2().get(listSize2 - 1) == 3){
CanvasView.getRectangles().add(CanvasView.getRectangles2().get(CanvasView.getRectangles2().size() - 1));
CanvasView.getRectangles2().remove(CanvasView.getRectangles2().size() - 1);
CanvasView.getElements2().remove(CanvasView.getElements2().size() - 1);
CanvasView.getElements().add(3);
CanvasView.currentState = CanvasView.undoRedo.DoUndoRedo;
return true;
}
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onBackPressed() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Exit");
builder.setMessage("Are You Sure?");
builder.setNegativeButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
System.exit(0);
}
});
builder.setPositiveButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
AlertDialog alert = builder.create();
alert.show();
}
}
Activiti_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/rect"
tools:context="com.example.HW3.MainActivity" >
<com.example.HW3.CanvasView
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>
答案 0 :(得分：1)
我假设您已在res / layout / activity_main.xml中定义了CanvasView（并为其分配了一个id，说＆＃34; custom_view＆＃34;） 您不应该静态调用Canvas方法（直接从类本身），而是从Android创建的实际实例。您可以通过将MainActivity更改为以下内容来获取它：
public class MainActivity extends Activity {
private CanvasView canvasView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.activity_main);
canvasView = findViewById(R.id.custom_view)
}
...
@Override
public boolean onOptionsItemSelected(MenuItem item) {
...
canvasView.invalidate();
...
}
答案 1 :(得分：0)
您提到invalidate()不是静态方法的错误状态。您确定要拨打myCanvasInstance.invalidate()和不 CanvasView.invalidate()吗？
请参阅下面的代码，以便更清楚：
protected void onCreate(Bundle savedInstanceState) {
// This won't work.
CanvasView.invalidate();
// This will.
CanvasView myView = new CanvasView();
myView.invalidate();
}
实际上，您的代码似乎将所有方法调用视为静态调用。我不知道这是否是一个拼写错误，或者你真的在你的代码中这样做。问题是，这不是正确的方法 - CanvasView是一个类，而不是一个实例/对象。您应该与实例进行交互，而不是与类进行交互。
对于初学者，更改这些行（以及与其相似的所有行）：
CanvasView.getElements().size();
CanvasView.getElements2().add(1);
CanvasView.getLines().remove(CanvasView.getLines().size() - 1);
etc.
看起来像这样：
// Define this on the top of your class (outside of any methods).
CanvasView myView;
// Do this on your onCreate() method.
myView = new CanvasView();
// ..and then code like these WILL work; even outside of onCreate().
myView.invalidate();
myView.getElements().size();
myView.getElements2().add(1);
myView.getLines().remove(CanvasView.getLines().size() - 1);
etc.
希望这有助于你。