android画板案例

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思路： 模仿电脑端的画图功能。

效果展示

目录结构

代码

• MainActivity

package com.example.www.paintboard;

import android.Manifest;
import android.annotation.SuppressLint;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.net.Uri;
import android.os.Environment;
import android.os.SystemClock;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;

public class MainActivity extends AppCompatActivity {

    private ImageView mIv;
    private Bitmap mCopyBitmap;
    private Paint mPaint;
    private Canvas mCanvas;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        requestPermissions(new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 100);

        //用来显示我们画的内容
        mIv = (ImageView) findViewById(R.id.imageView);

        Bitmap bitmap = BitmapFactory.decodeResource(this.getResources(), R.drawable.background);
        final Bitmap copyBitmap = copyBitmap(bitmap);

        mIv.setImageBitmap(copyBitmap);
        mIv.setOnTouchListener(new View.OnTouchListener() {

            int startX = 0;
            int startY = 0;

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                //获取当前事件的类型
                int action = event.getAction();
                switch (action) {
                    case MotionEvent.ACTION_DOWN:
                        System.out.println("触摸view");
                        //获取开始位置
                         startX = (int)event.getX();
                         startY = (int)event.getY();

                        break;
                    case MotionEvent.ACTION_MOVE:
                        System.out.println("移动view");
                        int stopX = (int)event.getX();
                        int stopY = (int)event.getY();
                        //不停地画线
                        mCanvas.drawLine(startX, startY, stopX, stopY, mPaint);
                        mIv.setImageBitmap(copyBitmap);
                        startX = stopX;
                        startY = stopY;

                        break;
                    case MotionEvent.ACTION_UP:
                        System.out.println("抬起view");
                        break;

                    default:
                        break;
                }
                return true;
            }
        });
    }

    /**
     * 创建一个bitmap的副本
     *
     * @param
     * @return
     */
    public Bitmap copyBitmap(Bitmap bitmap) {
        // 相当于创建了一张白纸
        mCopyBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());
        // 创建一个画笔
        mPaint = new Paint();
        // 创建一个画布，把白纸铺到画布上
        mCanvas = new Canvas(mCopyBitmap);
        mCanvas.drawBitmap(bitmap, new Matrix(), mPaint); // 执行完copyBitmap里面才有内容
        return mCopyBitmap;
    }

    public void setStroken(View view) {

        mPaint.setStrokeWidth(5);
    }

    public void setRed(View view) {
        mPaint.setColor(Color.RED);
    }

    public void save(View view) {
        try {
            File file = new File(Environment.getExternalStorageDirectory().getPath(), SystemClock.uptimeMillis()+".png");
            FileOutputStream fos = new FileOutputStream(file);
            mCopyBitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);

            Toast.makeText(getApplicationContext(), "图片保存成功", Toast.LENGTH_SHORT).show();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

• activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">


    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="383dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toTopOf="@+id/linearLayout"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@android:color/white" />

    <LinearLayout
        android:id="@+id/linearLayout"
        android:layout_width="368dp"
        android:layout_height="66dp"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        android:orientation="horizontal"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent">

        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="red"
            android:onClick="setRed"/>

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="setStroken"
            android:text="加粗" />

        <Button
            android:id="@+id/button3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="save"
            android:onClick="save"/>
    </LinearLayout>
</android.support.constraint.ConstraintLayout>

• AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.www.paintboard">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>