Android多媒体之画画板开发案例分享

public class MainActivity extends Activity implements OnClickListener,OnSeekBarChangeListener {

  private View red_view,green_view,blue_view;   //控制画笔颜色的三块区域
  private SeekBar seekBar;    //控制画笔粗细的拖动条
  private ImageView iv;  
  private Bitmap bitmap,backgroud;  //画纸和背景图
  private Canvas canvas;       //画布
  private Paint paint;        //画笔
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    red_view = findViewById(R.id.red_view);
    green_view = findViewById(R.id.green_view);
    blue_view = findViewById(R.id.blue_view);
    seekBar = (SeekBar) findViewById(R.id.seekbar);
    iv = (ImageView) findViewById(R.id.iv);
    iv.setImageResource(R.drawable.bg);
    //拿到背景图
    backgroud = BitmapFactory.decodeResource(getResources(), R.drawable.bg);
    //拿到和背景图一样大小的画纸
    bitmap = Bitmap.createBitmap(backgroud.getWidth(), backgroud.getHeight(), backgroud.getConfig());
    //把画纸固定在画布上
    canvas = new Canvas(bitmap);
    //拿到画笔
    paint = new Paint();
    paint.setColor(Color.BLACK);//设置画笔颜色为黑色
    paint.setStyle(Style.STROKE);//设置画笔为空心
    //添加处理规则
    Matrix matrix = new Matrix();
    //照着背景图画
    canvas.drawBitmap(backgroud, matrix, paint);
    red_view.setOnClickListener(this);
    green_view.setOnClickListener(this);
    blue_view.setOnClickListener(this);
    seekBar.setOnSeekBarChangeListener(this);
    iv.setOnTouchListener(new OnTouchListener() {
      float startX;
      float startY;
      @Override
      public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
        //获取按下时的坐标
        case MotionEvent.ACTION_DOWN:
          startX = event.getX();
          startY = event.getY();
          break;
        //获取移动时的坐标
        case MotionEvent.ACTION_MOVE:
          float stopX = event.getX();
          float stopY = event.getY();
//          // 在开始和结束坐标间画一条线
          canvas.drawLine(startX, startY, stopX, stopY, paint);
          //实时更新坐标（通过不断画线）
          startX = event.getX();
          startY = event.getY();

          iv.setImageBitmap(bitmap);
          break;
        case MotionEvent.ACTION_UP:
          break;
        default:
          break;
        }
        return true;
      }
    });
  }
  @Override
  public void onClick(View v) {
    switch (v.getId()) {
    case R.id.red_view:
      //当点击红色区域的时候设置画笔颜色为红色
      paint.setColor(Color.RED);
      break;
    case R.id.green_view:
      //当点击绿色区域的时候设置画笔颜色为绿色
      paint.setColor(Color.GREEN);
      break;
    case R.id.blue_view:
      //当点击蓝色区域的时候设置画笔颜色为蓝色
      paint.setColor(Color.BLUE);
      break;
    default:
      break;
    }
  }
  //拖动条的值改变的时候调用
  @Override
  public void onProgressChanged(SeekBar seekBar, int progress,
      boolean fromUser) {

  }
  //开始拖动时调用
  @Override
  public void onStartTrackingTouch(SeekBar seekBar) {

  }
  //停止拖动时调用
  @Override
  public void onStopTrackingTouch(SeekBar seekBar) {
    int progress = seekBar.getProgress();//拖动条默认的最大值为100
    paint.setStrokeWidth(progress/10f);//控制画笔的粗细范围（0-10）
  }
}