android TextView 垂直自動滾動字幕實現

前段時間，在網上搜到一個帖子，textview 水平自動滾動字幕的實現，今日項目需要垂直滾動字幕。其實現原理和水品一樣。都是重寫textview的onDraw方法。
實現垂直自動滾動字幕需要2點需要注意
1.需要根據textview的寬度和字體的大小計算滾動字幕有多少行。實現這個功能，需要重新寫兩個方法：1.onMeasure,2.onDraw.因為需要獲取textview的寬度，于是需要在onMeasure方法里面調用如下代碼。具體方法如下：

public VerticalScrollTextView extends TextView {
    private float step =0f;

    private Paint mPaint;
    private String text;
    private float width;
    private List<String> textList = new ArrayList<String>();    //分行保存textview的顯示信息。


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


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

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    width = MeasureSpec.getSize(widthMeasureSpec);   
          final int widthMode = MeasureSpec.getMode(widthMeasureSpec);  
    if (widthMode != MeasureSpec.EXACTLY) {   
        throw new IllegalStateException("ScrollLayout only canmCurScreen run at EXACTLY mode!");
    }      

    float length = 0;        
      if(text==null|text.length()==0){
            return ;
        }


        //下面的代碼是根據寬度和字體大小，來計算textview顯示的行數。

    textList.clear();

    StringBuilder builder = new StringBuilder();
    for(int i=0;i<text.length();i++){
        Log.e("textviewscroll",""+i+text.charAt(i));
        if(length<width){
            builder.append(text.charAt(i));
            length += mPaint.measureText(text.substring(i, i+1));
            if(i==text.length()-1){
                Log.e("textviewscroll",""+i+text.charAt(i));
                textList.add(builder.toString());
            }
        }else{
            textList.add(builder.toString().substring(0,builder.toString().length()-1));
        builder.delete(0, builder.length()-1) ;
        length= mPaint.measureText(text.substring(i, i+1));
        i--;
        }

    }
}


//下面代碼是利用上面計算的顯示行數，將文字畫在畫布上，實時更新。

&nbsp; &nbsp;&nbsp; @Override
    public void onDraw(Canvas canvas) {
        for (int i = 0; i < textList.size(); i++) {
            canvas.drawText(textList.get(i), 0, this.getHeight()+(i+1)*mPaint.getTextSize()-step, getPaint());
        }

    invalidate();    
    step = step+0.3f;
    if (step >= this.getHeight()+textList.size()*mPaint.getTextSize()) {
        step = 0;
    }        
}


}</pre> 
還有一些擴展功能沒有加，比方說滾動的速度設定，滾動多長時間就停止滾動。



轉自：http://blog.csdn.net/fengyoujie/article/details/7296941