讓ProgressBar居於真個螢幕在正中間：

xml佈局檔案如下：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:gravity="center" >

    <com.freesonfish.progress_bar.MyProgressBar2
        android:id="@+id/my_progress_bar_2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:background="@drawable/bitmap"
        android:visibility="gone" />

</LinearLayout>
 

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.Shader;
import android.graphics.SweepGradient;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.View;
import android.view.Window;

public class MyProgressBar2 extends View {

	private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
	private float mRotate;
	private Matrix mMatrix = new Matrix();
	private Shader mShader;
	private float x = 50.0f, y = 50.0f;
	private Activity activity;

	public MyProgressBar2(Context context, AttributeSet attr) {
		super(context, attr);
		this.activity = ((Activity) context);
		initPaint();
	}

	public MyProgressBar2(Context context) {
		super(context);
		this.activity = ((Activity) context);
		initPaint();
	}

	private void initPaint() {
		mShader = new SweepGradient(x, y, new int[] { 0x66378300, 0xFF378300 }, new float[] { 0.7f, 0.7f });
		mPaint.setShader(mShader);
		mPaint.setStyle(Paint.Style.STROKE);
		mPaint.setStrokeWidth(10);
		mPaint.setAntiAlias(true);
	}

	@Override
	protected void onDraw(Canvas canvas) {
		Paint paint = mPaint;
		mMatrix.setRotate(mRotate, x, y);
		mShader.setLocalMatrix(mMatrix);
		mRotate += 5;
		if (mRotate >= 360) {
			mRotate = 0;
		}
		invalidate();
		canvas.drawCircle(x, y, 40, paint);
	}

	protected void setLoaction() {
		DisplayMetrics dm = new DisplayMetrics();
		activity.getWindowManager().getDefaultDisplay().getMetrics(dm);
		x = dm.widthPixels / 2.0f;
		y = (dm.heightPixels - getContentPosition()) / 2.0f;
		initPaint();
		invalidate();
	}

	private int getContentPosition() {
		Rect rect = new Rect();
		Window window = activity.getWindow();
		window.getDecorView().getWindowVisibleDisplayFrame(rect);
		return window.findViewById(Window.ID_ANDROID_CONTENT).getTop();
	}
}
 

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;

import com.freesonfish.R;

public class MyprogressBarActivity2 extends Activity {

	MyProgressBar2 progressBar = null;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.my_progress_bar_2);

		progressBar = (MyProgressBar2) findViewById(R.id.my_progress_bar_2);
		new Handler().postDelayed(new Runnable() {

			@Override
			public void run() {
				progressBar.setLoaction();
				progressBar.setVisibility(View.VISIBLE);
			}
		}, 400);

	}

}