Android学习笔记绘制图片

Android绘制位图的两个类

BitmapFactory创建位图的方法

案例代码

先用Device File Explorer在模拟器的sdcard目录中放入图片tx3.png

MyView.java

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Environment;
import android.view.View;

public class MyView extends View {


    public MyView(Context context) {
        super(context);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint();//定义画笔
        String path = Environment.getExternalStorageDirectory()+"/tx3.png";//读取文件路径
        Bitmap bitmap = BitmapFactory.decodeFile(path);//创建位图
        //绘制位图
        canvas.drawBitmap(bitmap,0,0,paint);

        //挖出一小块区域
        Bitmap bitmap1 = Bitmap.createBitmap(bitmap,163,
                189,150,168);
        canvas.drawBitmap(bitmap1,270,550,paint);
    }
}

MainActivty.java

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.FrameLayout;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //获取帧布局管理器
        FrameLayout frameLayout = findViewById(R.id.frameLayout);
        frameLayout.addView(new MyView(this));//将自定义View添加到布局管理器中
    }   
}

manifests中开放权限

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

在模拟器中开放应用权限

效果图