Android菜鳥的成長筆記（27）——SurfaceView的使用
阿新 • • 發佈：2017-07-26
llb white avi red .get 時也 Y軸 ++ watermark
前面有關自己定義View中進行了畫圖。但View的畫圖機制存在例如以下缺陷：
1、View缺乏雙緩沖機制。
2、當程序須要更新View上的圖像時，程序必須重繪View上顯示的整張圖片。
3、新線程無法直接更新View組件。
因為View存在上面缺陷。所以在遊戲開發中一般使用SurfaceView來進行繪制，SurfaceView通常會與SurfaceHolder結合使用。SurfaceHolder用於向與之關聯的SurfaceView上畫圖，調用SurfaceView的getHolder()方法就可以獲取SurfaceView關聯的SurfaceHolder.
SurfaceHolder提供了例如以下方法來獲取Canvas對象：
1、Canvas lockCanvas():鎖定整個SurfaceView對象，獲取該Surface上的Canvas.
2、Canvas lockCanvas(Rect dirty):鎖定SurfaceView上Rect劃分的區域。獲取該Surface上的Canvas.
兩個方法返回的是同一個Canvas,可是第二個方法僅僅對圈出來的區域進行刷新，Canvas畫圖完畢後通過unlockCanvasAndPost(canvas)方法來釋放畫布，提交改動。當調用SurfaceHolder的unlockCanvasAndPost方法之後。該方法之前所繪制的圖形還處於緩沖之下。下一次lockCanvas()方法鎖定的區域可能會“遮擋”它。
package com.example.erweimatest;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;
import android.view.View;
import android.view.View.OnTouchListener;
public class SurfaceViewTest extends Activity {
private SurfaceHolder holder;
private Paint paint;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
paint = new Paint();
SurfaceView surface = (SurfaceView) findViewById(R.id.show);
//初始化SurfaceHolder對象
holder = surface.getHolder();
holder.addCallback(new Callback() {
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
//鎖定整個SurfaceView
Canvas canvas = holder.lockCanvas();
//繪制背景
Bitmap back = BitmapFactory.decodeResource(SurfaceViewTest.this.getResources(), R.drawable.bg);
//繪制背景
canvas.drawBitmap(back, 0, 0, null);
//繪制完畢。釋放畫布，提交改動
holder.unlockCanvasAndPost(canvas);
//又一次鎖一次，“持久化”上次所繪制內容
//本次lockCanvas會遮擋上次lockCanvas
holder.lockCanvas(new Rect(0, 0, 0, 0));
holder.unlockCanvasAndPost(canvas);
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
// TODO Auto-generated method stub
}
});
surface.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
if(event.getAction() == MotionEvent.ACTION_DOWN){
int cx = (int) event.getX();
int cy = (int) event.getY();
//鎖定SurfaceView的布局區域，僅僅更新局部內容
Canvas canvas = holder.lockCanvas(new Rect(cx - 50, cy - 50, cx + 50, cy + 50));
//保存canvas當前狀態
canvas.save();
//旋轉畫布
canvas.rotate(30, cx, cy);
paint.setColor(Color.RED);
//繪制紅色方塊
canvas.drawRect(cx - 40, cy - 40, cx, cy, paint);
//恢復canvas之前的保存狀態
canvas.restore();
paint.setColor(Color.GREEN);
//繪制綠色方塊
canvas.drawRect(cx, cy, cx + 40, cy + 40, paint);
//繪制完畢，釋放畫布。提交改動
holder.unlockCanvasAndPost(canvas);
}
return false;
}
});
}
}
<?xml version="1.0" encoding="utf-8"?執行效果：> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <SurfaceView android:id="@+id/show" android:layout_width="fill_parent" android:layout_height="fill_parent" /> </LinearLayout>
能夠看出來，第一次繪制的圖形會被第二次的區域遮擋，第三次繪制的圖形可能遮擋第二次繪制的區域。但不會遮擋第一次的區域。假設第二次繪制的區域被第三次的區域所遮擋，第一次所繪制的圖形可能顯露出來。
基於SurfaceView開發的示波器：
package com.example.erweimatest;
import java.util.Timer;
import java.util.TimerTask;
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class ShowVawe extends Activity{
private SurfaceHolder holder;
private Paint paint;
final int HEIGHT = 320;
final int WIDTH = 320;
final int X_OFFSET = 5;
private int cx = X_OFFSET;
//實際的Y軸的位置
int centerY = HEIGHT / 2;
Timer timer = new Timer();
TimerTask task = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final SurfaceView surface = (SurfaceView) findViewById(R.id.show);
//初始化SurfaceHolder對象
holder = surface.getHolder();
paint = new Paint();
paint.setColor(Color.GREEN);
paint.setStrokeWidth(3);
Button sin = (Button) findViewById(R.id.sin);
Button cos = (Button) findViewById(R.id.cos);
OnClickListener listener = (new OnClickListener() {
@Override
public void onClick(final View source) {
drawBack(holder);
cx = X_OFFSET;
if(task != null){
task.cancel();
}
task = new TimerTask() {
@Override
public void run() {
int cy = source.getId() == R.id.sin ? centerY - (int)(100 * Math.sin((cx - 5) * 2 * Math.PI / 150))
: centerY - (int)(100 * Math.cos((cx - 5) * 2 * Math.PI / 150));
Canvas canvas = holder.lockCanvas(new Rect(cx, cy - 2, cx+2, cy + 2));
canvas.drawPoint(cx, cy, paint);
cx ++;
if(cx > WIDTH){
task.cancel();
task = null;
}
holder.unlockCanvasAndPost(canvas);
}
};
timer.schedule(task, 0, 30);
}
});
sin.setOnClickListener(listener);
cos.setOnClickListener(listener);
holder.addCallback(new Callback() {
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
// TODO Auto-generated method stub
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
// TODO Auto-generated method stub
}
});
}
private void drawBack(SurfaceHolder holder){
Canvas canvas = holder.lockCanvas();
//繪制白色背景
canvas.drawColor(Color.WHITE);
Paint p = new Paint();
p.setColor(Color.BLACK);
p.setStrokeWidth(2);
//繪制坐標軸
canvas.drawLine(X_OFFSET, centerY, WIDTH, centerY, p);
canvas.drawLine(X_OFFSET, 40, X_OFFSET, HEIGHT, p);
holder.unlockCanvasAndPost(canvas);
holder.lockCanvas(new Rect(0, 0, 0, 0));
holder.unlockCanvasAndPost(canvas);
}
}
activity_main.xml<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center" > <Button android:id="@+id/sin" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="正旋曲線" /> <Button android:id="@+id/cos" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="余旋曲線" /> </LinearLayout> <SurfaceView android:id="@+id/show" android:layout_width="fill_parent" android:layout_height="fill_parent" android:gravity="center" /> </LinearLayout>執行結果：
當程序每次繪制正旋波、余旋波上的當前點時，程序無須重繪整個畫面。SurfaceHolder僅僅要鎖定當前繪制點的小範圍就可以，系統更新畫面時也僅僅要更新這個範圍就可以。
Android菜鳥的成長筆記（27）——SurfaceView的使用