Androidx学习笔记（75）--- 画画板

画画板

记录用户触摸事件的XY坐标，绘制直线 * 给ImageView设置触摸侦听，得到用户的触摸事件，并获知用户触摸ImageView的坐标

    iv.setOnTouchListener(new OnTouchListener() {        @Override        public boolean onTouch(View v, MotionEvent event) {            // TODO Auto-generated method stub            switch (event.getAction()) {            //触摸屏幕            case MotionEvent.ACTION_DOWN:                //得到触摸屏幕时手指的坐标                startX = (int) event.getX();                startY = (int) event.getY();                break;            //在屏幕上滑动            case MotionEvent.ACTION_MOVE:                //用户滑动手指，坐标不断的改变，获取最新坐标                int newX = (int) event.getX();                int newY = (int) event.getY();                //用上次onTouch方法得到的坐标和本次得到的坐标绘制直线                canvas.drawLine(startX, startY, newX, newY, paint);                iv.setImageBitmap(copyBm);                startX = newX;                startY = newY;                break;            }            return true;        }    });

• 刷子效果，加粗画笔

  paint.setStrokeWidth(8);

• 调色板，改变画笔颜色

  paint.setColor(Color.GREEN);

• 保存图片至SD卡

  FileOutputStream fos = null;try {    fos = new FileOutputStream(new File("sdcard/dazuo.png"));} catch (FileNotFoundException e) {    // TODO Auto-generated catch block    e.printStackTrace();}//保存图片copyBm.compress(CompressFormat.PNG, 100, fos);

• 系统每次收到SD卡就绪广播时，都会去遍历sd卡的所有文件和文件夹，把遍历到的所有多媒体文件都在MediaStore数据库保存一个索引，这个索引包含多媒体文件的文件名、路径、大小
• 图库每次打开时，并不会去遍历sd卡获取图片，而是通过内容提供者从MediaStore数据库中获取图片的信息，然后读取该图片

• 系统开机或者点击加载sd卡按钮时，系统会发送sd卡就绪广播，我们也可以手动发送就绪广播

  Intent intent = new Intent();intent.setAction(Intent.ACTION_MEDIA_MOUNTED);intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));sendBroadcast(intent);

打开模拟器选项，便于调试观察

public class MainActivity extends Activity {
 
private ImageView iv;
 
int startX;
int startY;
 
private Canvas canvas;
 
private Paint paint;
 
private Bitmap bmCopy;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//加载画画板的背景图
Bitmap bmSrc = BitmapFactory.decodeResource(getResources(), R.drawable.bg);
bmCopy = Bitmap.createBitmap(bmSrc.getWidth(), bmSrc.getHeight(), bmSrc.getConfig());
paint = new Paint();
canvas = new Canvas(bmCopy);
//绘制
canvas.drawBitmap(bmSrc, new Matrix(), paint);
iv = (ImageView) findViewById(R.id.iv);
iv.setImageBitmap(bmCopy);
//设置触摸侦听
iv.setOnTouchListener(new OnTouchListener() {
//触摸屏幕时，触摸事件产生时，此方法调用
@Override
public boolean onTouch(View v, MotionEvent event) {
int action = event.getAction();
switch (action) {
//用户手指摸到屏幕
case MotionEvent.ACTION_DOWN:
startX = (int) event.getX();
startY = (int) event.getY();
break;
//用户手指正在滑动
case MotionEvent.ACTION_MOVE:
int x = (int) event.getX();
int y = (int) event.getY();
canvas.drawLine(startX, startY, x, y, paint);
//每次绘制完毕之后，本次绘制的结束坐标变成下一次绘制的初始坐标
startX = x;
startY = y;
iv.setImageBitmap(bmCopy);
break;
//用户手指离开屏幕
case MotionEvent.ACTION_UP:
break;
 
}
//true：告诉系统，这个触摸事件由我来处理
//false：告诉系统，这个触摸事件我不处理，这时系统会把触摸事件传递给imageview的父节点
return true;
}
});
}
    
    //设置颜色
public void red(View v){
paint.setColor(Color.RED);
}
public void green(View v){
paint.setColor(Color.GREEN);
}
    
    //设置画刷
public void brush(View v){
paint.setStrokeWidth(7);
}
    
    //保存
public void save(View v){
File file = new File("sdcard/dazuo.png");
FileOutputStream fos = null;
try {
fos = new FileOutputStream(file);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
bmCopy.compress(CompressFormat.PNG, 100, fos);
//发送sd卡就绪广播
Intent intent = new Intent();
intent.setAction(Intent.ACTION_MEDIA_MOUNTED);
intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));
sendBroadcast(intent);
}
}