拖动 ImageView 和绘图 - Android Studio 4.0

问题描述

我正在尝试制作一个需要在屏幕中拖动 ImageView 时画一条线的应用程序。我试图在 LinearLayouts 下创建一个画布，但是当我拖动对象时它没有绘制。请帮我！这是来自 MainActivity、CanvasView 类和 xml 文件的代码。我不知道我应该如何从 CanvasView 类调用 onTouchEvent 方法。当我触摸该图标时，它会创建一个阴影，但不会绘制超出我预期的线条。

package com.example.drawview;

import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;
import android.content.ClipData;
import android.content.Context;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;

public class MainActivity extends AppCompatActivity {

    private CanvasView canvasView;
    private ConstraintLayout mainLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViewById(R.id.imageView).setonTouchListener(new TouchEventView(this));

        mainLayout = findViewById(R.id.screen);
        canvasView = (CanvasView) findViewById(R.id.canvas);
    }

    public class TouchEventView extends View implements View.OnTouchListener {

        public TouchEventView(Context context) {
            super(context);
        }
        
        @Override
        public boolean onTouch(View ve,MotionEvent event) {
            canvasView.onTouchEvent(event);
            ClipData data = ClipData.newPlainText("simple_text","text");
            View.DragShadowBuilder sb = new View.DragShadowBuilder(ve);
            ve.startDrag(data,sb,ve,0);
            return true;
        }
    }
}

package com.example.drawview;

import android.content.ClipData;
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.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import androidx.annotation.Nullable;

public class CanvasView extends View {

    public int height;
    public int width;
    private Bitmap mBitmap;
    private Canvas mCanvas;
    private Path mPath;
    private Paint mPaint;
    private float mX,mY;
    private final float TOLERANCE = 5;
    Context context;

    public CanvasView(Context context,@Nullable AttributeSet attrs) {
        super(context,attrs);
        this.context = context;

        mPath = new Path();

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setColor(Color.GREEN);
        mPaint.setStyle(Paint.Style.stroke);
        mPaint.setstrokeJoin(Paint.Join.ROUND);
        mPaint.setstrokeWidth(4f);
    }

     /*

    public CanvasView(Context context) {
        super(context);
        this.context = context;

        mPath = new Path();

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setColor(Color.GREEN);
        mPaint.setStyle(Paint.Style.stroke);
        mPaint.setstrokeJoin(Paint.Join.ROUND);
        mPaint.setstrokeWidth(4f);
    }


     */

    @Override
    protected void onSizeChanged(int w,int h,int oldw,int oldh) {
        super.onSizeChanged(w,h,oldw,oldh);

        mBitmap = Bitmap.createBitmap(w,Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPath(mPath,mPaint);
    }

    private void startTouch(float x,float y){
        mPath.moveto(x,y);
        mX = x;
        mY = y;
    }

    private void movetouch(float x,float y){
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y - mY);
        if(dx >= TOLERANCE || dy >= TOLERANCE){
            mPath.quadTo(mX,mY,(x + mX)/2,(y + mY)/2);
            mX = x;
            mY = y;
        }
    }

    public void clearCanvas(){
        mPath.reset();
        invalidate();
    }

    private void upTouch(){
        mPath.lineto(mX,mY);
    }

    public boolean onTouchEvent(MotionEvent event) {
        float xPos = event.getX();
        float yPos = event.getY();

        switch (event.getAction()){
            case MotionEvent.ACTION_DOWN:
                startTouch(xPos,yPos);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                movetouch(xPos,yPos);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                upTouch();
                invalidate();
                break;
        }
        return true;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/screen"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.example.drawview.CanvasView
        android:id="@+id/canvas"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:visibility="visible"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentDescription="@string/todo"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_launcher_foreground" />

</androidx.constraintlayout.widget.ConstraintLayout>

解决方法

暂无找到可以解决该程序问题的有效方法，小编努力寻找整理中！

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