简单概述
在日常生活中，我们经常会突发一些奇思妙想，或是一个画面，或是几个符号。这时候无法使用拍照或者打字功能实现，想拿笔记下又身边找不到笔。于是我琢磨能不能做一个手机端的画板。
效果图
实现过程
项目布局很简单
让我们来看代码：首先声明画笔，画板，和坐标
public class MainActivity extends AppCompatActivity{
Paint paint;
Canvas canvas;
ImageView imageview;
Bitmap bitmap,newbitmap;
TextView tv_stroke;
int startX, startY, endX, endY;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_paint_tools);
LinearLayout ll_layout = findViewById(R.id.ll_layout);
RadioGroup rg_color = findViewById(R.id.rg_color);
遍历单选按钮，当单选按钮选中时，获取单选按钮颜色并将画笔颜色设置当前按钮的文本颜色，最后注意要设置画笔宽度，以免在后面点橡皮擦的时候画笔宽度调不回来
for (int i = 0;i<rg_color.getChildCount();i++){
RadioButton rb = (RadioButton) rg_color.getChildAt(i);
rb.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
if (buttonView.isChecked()){
paint.setColor(buttonView.getTextColors().getDefaultColor());
paint.setStrokeWidth(5);
}
}
});
}
首先创建一张空白图片和一张灰色画布，将图片放在画布上面
imageview = findViewById(R.id.imageview);
Log.i("MyPaintToolsActivity",imageview.getWidth()+" "+imageview.getHeight());
Point point = new Point();
getWindowManager().getDefaultDisplay().getSize(point);
Log.i("MyPaintToolsActivity",point.x+" "+point.y);
bitmap = Bitmap.createBitmap(888,1200,Bitmap.Config.ARGB_8888);
canvas = new Canvas(bitmap);
canvas.drawColor(Color.argb(100,0,0,0));
paint = new Paint();
paint.setStrokeWidth(5);
paint.setAntiAlias(true);
paint.setColor(Color.RED);
canvas.drawBitmap(bitmap,new Matrix(),paint);
imageview.setImageBitmap(bitmap);
注册触摸监听事件,获取鼠标按下时的坐标和鼠标移动后的坐标。在开始和结束之间画一条直线并更新画布图片
imageview.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:
Log.i("MyPaintToolsActivity","ACTION_DOWN");
startX = (int) (event.getX()/1.4);
startY = (int) (event.getY()/1.4);
break;
case MotionEvent.ACTION_MOVE:
Log.i("MyPaintToolsActivity","ACTION_MOVE");
endX = (int) (event.getX()/1.4);
endY = (int) (event.getY()/1.4);
canvas.drawLine(startX,startY,endX,endY,paint);
startX = (int) (event.getX()/1.4);
startY = (int) (event.getY()/1.4);
imageview.setImageBitmap(bitmap);
break;
case MotionEvent.ACTION_UP:
Log.i("MyPaintToolsActivity","ACTION_UP");
break;
}
imageview.invalidate();
return true;
}
});
清屏的话就一行代码 ，剩下的是重新生成一块画布
Button btn_clear = findViewById(R.id.btn_clear);
btn_clear.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvas.drawColor(0,PorterDuff.Mode.CLEAR);
bitmap = Bitmap.createBitmap(888,1200,Bitmap.Config.ARGB_8888);
canvas = new Canvas(bitmap);
canvas.drawColor(Color.argb(100,0,0,0));
paint = new Paint();
paint.setStrokeWidth(5);
paint.setAntiAlias(true);
paint.setColor(Color.RED);
canvas.drawBitmap(bitmap,new Matrix(),paint);
imageview.setImageBitmap(bitmap);
}
});
呃，这里会把画布擦掉…也就是擦成白色…
// 擦除
Button btn_eraser = findViewById(R.id.btn_eraser);
btn_eraser.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
paint.setColor(Color.rgb(250,250,250));
paint.setStrokeWidth(30);
}
});
}
}
最后看看页面布局
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:orientation="vertical"
android:id="@+id/ll_layout">
<!-- tools:context=".MyPaintToolsActivity">-->
<ImageView
android:id="@+id/imageview"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1" />
<RadioGroup
android:background="#747373"
android:layout_width="match_parent"
android:orientation="horizontal"
android:id="@+id/rg_color"
android:layout_height="wrap_content">
<RadioButton
android:id="@+id/rb_red"
android:layout_width="wrap_content"
android:layout_height="43dp"
android:layout_weight="1"
android:text="红色"
android:textColor="#FF0000"
android:textSize="18sp" />
<RadioButton
android:id="@+id/rb_green"
android:layout_width="wrap_content"
android:layout_height="30dp"
android:layout_weight="1"
android:text="黑色"
android:textColor="#000000"
android:textSize="18sp" />
<RadioButton
android:id="@+id/rb_blue"
android:layout_width="wrap_content"
android:layout_height="30dp"
android:layout_weight="1"
android:text="白色"
android:textColor="#FFFFFF"
android:textSize="18sp" />
</RadioGroup>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal">
<Button
android:id="@+id/btn_clear"
android:layout_width="wrap_content"
android:layout_weight="1"
android:layout_height="wrap_content"
android:background="#000000"
android:textColor="#FFFFFF"
android:textSize="18sp"
android:text="清除"/>
<Button
android:id="@+id/btn_eraser"
android:layout_width="wrap_content"
android:layout_weight="1"
android:layout_height="wrap_content"
android:textColor="#FFFFFF"
android:textSize="18sp"
android:background="#000000"
android:text="擦除"/>
</LinearLayout>
</LinearLayout>
作者：陈彦熹
原文链接：link