三种方式绘制图片

转自：http://www.cnblogs.com/renhui/p/7456956.html

1. ImageView 绘制图片

package com.ddx.testimageview;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;

import java.io.File;

public class ShowImageView extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_show_image_view);
        //Bitmap bitmap = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory().getPath() + File.separator + "11.jpg");
        Bitmap bitmap = BitmapFactory.decodeFile(Environment.getDataDirectory().getPath() + File.separator + "11.jpg");
        Log.d("DDX", "externalStorageDirectory = " + Environment.getExternalStorageDirectory().getPath() + File.separator + "11.jpg");
        ImageView imageView = (ImageView) findViewById(R.id.imageView);
        imageView.setImageBitmap(bitmap);
    }
}

2. SurfaceView绘制图片

package com.ddx.testimageview;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.ImageView;

import java.io.File;

public class ShowImageView extends AppCompatActivity {

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

        SurfaceView surfaceView = (SurfaceView) findViewById(R.id.surfaceView);
        surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder surfaceHolder) {
                if(surfaceHolder == null)
                    return;

                Paint paint = new Paint();
                paint.setAntiAlias(true);
                paint.setStyle(Paint.Style.STROKE);

                Bitmap bitmap = BitmapFactory.decodeFile(Environment.getDataDirectory().getPath() + File.separator + "11.jpg");//获取Bitmap

                Canvas canvas = surfaceHolder.lockCanvas();//先锁定当前surfaceView的画面
                canvas.drawBitmap(bitmap, 0, 0, paint);//执行绘制操作
                surfaceHolder.unlockCanvasAndPost(canvas);//解决锁定并显示在界面上
            }

            @Override
            public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {

            }

            @Override
            public void surfaceDestroyed(SurfaceHolder surfaceHolder) {

            }
        });


    }
}

 3. 自定义View绘制图片

https://blog.csdn.net/iwanghang/article/details/54018759

package com.ddx.customview;

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

import java.io.File;

/**
 * Created by dingdx on 2018/7/19.
 */

public class NewView extends View {
    Paint mPaint = new Paint();
    Bitmap mBitmap;

    public NewView(Context context) {
        super(context);
        mPaint.setAntiAlias(true);
        mPaint.setStyle(Paint.Style.STROKE);
        mBitmap = BitmapFactory.decodeFile(Environment.getDataDirectory().getPath() + File.separator + "11.jpg");
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 不建议在onDraw做任何分配内存的操作
        if(mBitmap != null) {
            canvas.drawBitmap(mBitmap,0,0,mPaint);
        }
        /*mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        //mPaint.setColor(Color.BLUE);
        mPaint .setColor(Color.argb(60, 0, 0, 0));
        canvas.drawCircle(300,300,200,mPaint);*/
    }
}

注：如果是getExternalStorageDirectory别忘记了权限，否则是不会展示成功的。

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