Android控件TextProgressBar进度条上显文字

Android系统的进度条控件默认的设计的不是很周全，比如没有包含文字的显示，那么如何在Android进度条控件上显示文字呢? 来自Google内部的代码来了解下，主要使用的addView这样的方法通过覆盖一层Chronometer秒表控件来实现，整个代码如下 :

 public class TextProgressBar extends RelativeLayout implements OnChronometerTickListener {
    public static final String TAG = "TextProgressBar"; 
    
    static final int CHRONOMETER_ID = android.R.id.text1;
    static final int PROGRESSBAR_ID = android.R.id.progress;
    
    Chronometer mChronometer = null;
    ProgressBar mProgressBar = null;
    
    long mDurationBase = -1;
    int mDuration = -1;

    boolean mChronometerFollow = false;
    int mChronometerGravity = Gravity.NO_GRAVITY;
    
    public TextProgressBar(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public TextProgressBar(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

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

    //Android开发网提示关键部分在这里


    @Override
    public void addView(View child, int index, ViewGroup.LayoutParams params) {
        super.addView(child, index, params);
        
        int childId = child.getId();
        if (childId == CHRONOMETER_ID && child instanceof Chronometer) {
            mChronometer = (Chronometer) child;
            mChronometer.setOnChronometerTickListener(this);
            
            // Check if Chronometer should move with with ProgressBar 
            mChronometerFollow = (params.width == ViewGroup.LayoutParams.WRAP_CONTENT);
            mChronometerGravity = (mChronometer.getGravity() & Gravity.HORIZONTAL_GRAVITY_MASK);
            
        } else if (childId == PROGRESSBAR_ID && child instanceof ProgressBar) {
            mProgressBar = (ProgressBar) child;
        }
    }

 
    @android.view.RemotableViewMethod
    public void setDurationBase(long durationBase) {
        mDurationBase = durationBase;
        
        if (mProgressBar == null || mChronometer == null) {
            throw new RuntimeException("Expecting child ProgressBar with id " +
                    "'android.R.id.progress' and Chronometer id 'android.R.id.text1'");
        }
        
        // Update the ProgressBar maximum relative to Chronometer base
        mDuration = (int) (durationBase - mChronometer.getBase());
        if (mDuration <= 0) {
            mDuration = 1;
        }
        mProgressBar.setMax(mDuration);
    }
    
 
    public void onChronometerTick(Chronometer chronometer) {
        if (mProgressBar == null) {
            throw new RuntimeException(
                "Expecting child ProgressBar with id 'android.R.id.progress'");
        }
        
        // Stop Chronometer if we're past duration
        long now = SystemClock.elapsedRealtime();
        if (now >= mDurationBase) {
            mChronometer.stop();
        }

 
        int remaining = (int) (mDurationBase - now);
        mProgressBar.setProgress(mDuration - remaining);
        
   
        if (mChronometerFollow) {
            RelativeLayout.LayoutParams params;
            
 
            params = (RelativeLayout.LayoutParams) mProgressBar.getLayoutParams();
            int contentWidth = mProgressBar.getWidth() - (params.leftMargin + params.rightMargin);
            int leadingEdge = ((contentWidth * mProgressBar.getProgress()) /
                    mProgressBar.getMax()) + params.leftMargin;
            
 
            int adjustLeft = 0;
            int textWidth = mChronometer.getWidth();
            if (mChronometerGravity == Gravity.RIGHT) {
                adjustLeft = -textWidth;
            } else if (mChronometerGravity == Gravity.CENTER_HORIZONTAL) {
                adjustLeft = -(textWidth / 2);
            }
            
 
            leadingEdge += adjustLeft;
            int rightLimit = contentWidth - params.rightMargin - textWidth;
            if (leadingEdge < params.leftMargin) {
                leadingEdge = params.leftMargin;
            } else if (leadingEdge > rightLimit) {
                leadingEdge = rightLimit;
            }
            
            params = (RelativeLayout.LayoutParams) mChronometer.getLayoutParams();
            params.leftMargin = leadingEdge;
            
 
            mChronometer.requestLayout();
            
        }
    }
}