android学习4——View的长宽问题

画形状的时间经常会用到点的坐标,这时原点O的位置就非常重要.在像素为1280*720的设备上画一条直线.代码如下所示:

import android.app.Activity;
import android.os.Bundle;

public class WithTitleActivity  extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new DrawLineView(this));
    }
}

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;

public class DrawLineView  extends View {
    @Override
    protected void onDraw(Canvas canvas) {
        Paint paint = new Paint();
        paint.setColor(Color.WHITE);
        canvas.drawLine(0, 0, 720, 1280, paint);
        super.onDraw(canvas);
    }
    public WithTitleView(Context context) {
        super(context);
    }
}

设备像素是1280*720,希望画一条对角线,但代码的效果所下图所示:

并没有画对角线.是因为工具栏和名称的影响.设置成全屏,代码如下:

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;

public class WithoutTitleActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(
                WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(new DrawLineView(this));
    }
}