用Android studio写构建一个画板的文件。包括以下功能:1、修改描边宽度;2、更改画板颜色;3、擦除;4、全部清除;5、保存;6、退出。

以下是一个简单的画板应用程序的代码。包括所需的功能：修改描边宽度、更改画板颜色、擦除、全部清除、保存、退出。

MainActivity.java:

import android.Manifest;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.SeekBar;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import java.io.File;
import java.io.FileOutputStream;
import java.util.UUID;

public class MainActivity extends AppCompatActivity {

    private DrawingView drawingView;
    private SeekBar seekBar;
    private Button clearBtn, eraseBtn, saveBtn, exitBtn;
    private int strokeWidth = 4;
    private int currentColor = Color.BLACK;
    private boolean eraseMode = false;

    private static final int REQUEST_PERMISSION_WRITE_EXTERNAL_STORAGE = 1;

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

        drawingView = new DrawingView(this);
        LinearLayout layout = findViewById(R.id.layout);
        layout.addView(drawingView);

        seekBar = findViewById(R.id.seekBar);
        seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                strokeWidth = progress;
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        });

        clearBtn = findViewById(R.id.clearBtn);
        clearBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                drawingView.clear();
            }
        });

        eraseBtn = findViewById(R.id.eraseBtn);
        eraseBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                eraseMode = !eraseMode;
                if (eraseMode) {
                    eraseBtn.setText(R.string.draw_mode);
                } else {
                    eraseBtn.setText(R.string.erase_mode);
                }
            }
        });

        saveBtn = findViewById(R.id.saveBtn);
        saveBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                        != PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(MainActivity.this,
                            new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                            REQUEST_PERMISSION_WRITE_EXTERNAL_STORAGE);
                } else {
                    saveImage();
                }
            }
        });

        exitBtn = findViewById(R.id.exitBtn);
        exitBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });
    }

    private void saveImage() {
        String fileName = UUID.randomUUID().toString() + ".png";
        File file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), fileName);

        try {
            FileOutputStream fos = new FileOutputStream(file);
            Bitmap bitmap = drawingView.getBitmap();
            bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
            fos.flush();
            fos.close();
            Toast.makeText(this, R.string.image_saved, Toast.LENGTH_SHORT).show();
            Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
            intent.setData(Uri.fromFile(file));
            sendBroadcast(intent);
        } catch (Exception e) {
            e.printStackTrace();
            Toast.makeText(this, R.string.image_save_error, Toast.LENGTH_SHORT).show();
        }
    }

    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        if (requestCode == REQUEST_PERMISSION_WRITE_EXTERNAL_STORAGE) {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                saveImage();
            } else {
                Toast.makeText(this, R.string.permission_denied, Toast.LENGTH_SHORT).show();
            }
        } else {
            super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        }
    }

    public class DrawingView extends View {

        private Bitmap bitmap;
        private Canvas canvas;
        private Path path;
        private Paint paint;

        public DrawingView(Context context) {
            super(context);
            bitmap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);
            canvas = new Canvas(bitmap);
            path = new Path();
            paint = new Paint();
            paint.setColor(currentColor);
            paint.setStrokeWidth(strokeWidth);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);
            paint.setStrokeCap(Paint.Cap.ROUND);
            setDrawingCacheEnabled(true);
        }

        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);
            bitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
            canvas = new Canvas(bitmap);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);
            canvas.drawBitmap(bitmap, 0, 0, null);
            canvas.drawPath(path, paint);
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX();
            float y = event.getY();
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    path.moveTo(x, y);
                    break;
                case MotionEvent.ACTION_MOVE:
                    path.lineTo(x, y);
                    break;
                case MotionEvent.ACTION_UP:
                    canvas.drawPath(path, paint);
                    path.reset();
                    break;
                default:
                    return false;
            }
            invalidate();
            return true;
        }

        public void clear() {
            canvas.drawColor(Color.WHITE);
            invalidate();
        }

        public Bitmap getBitmap() {
            return getDrawingCache();
        }

        public void setColor(int color) {
            currentColor = color;
            paint.setColor(currentColor);
        }

        public void setStrokeWidth(int width) {
            strokeWidth = width;
            paint.setStrokeWidth(strokeWidth);
        }

        public void setEraseMode(boolean erase) {
            eraseMode = erase;
            if (erase) {
                paint.setColor(Color.WHITE);
            } else {
                paint.setColor(currentColor);
            }
        }
    }
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <SeekBar
        android:id="@+id/seekBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:max="20"
        android:progress="4"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/clearBtn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/clear"/>

        <Button
            android:id="@+id/eraseBtn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/erase_mode"/>

        <Button
            android:id="@+id/saveBtn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/save"/>

        <Button
            android:id="@+id/exitBtn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/exit"/>

    </LinearLayout>

</LinearLayout>

strings.xml:

<resources>
    <string name="app_name">My Drawing Board</string>
    <string name="clear">Clear</string>
    <string name="erase_mode">Erase Mode</string>
    <string name="draw_mode">Draw Mode</string>
    <string name="save">Save</string>
    <string name="exit">Exit</string>
    <string name="image_saved">Image saved successfully.</string>
    <string name="image_save_error">Error while saving image.</string>
    <string name="permission_denied">Permission denied.</string>
</resources>

在 AndroidManifest.xml 文件中添加以下权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />