android textView的渐入效果

1：自定义属性：

attrs：

  <declare-styleable name="RealText">
        <attr name="text" format="string"/>
        <attr name="duration" format="integer"/>

    </declare-styleable>

2：自定义View：

public class RealText extends TextView implements Runnable,ValueAnimator.AnimatorUpdateListener{

    private String text;
    private int duration = 300;
    private double[] alphas;
    private int red;
    private int green;
    private int blue;


    public RealText(Context context) {
        this(context, null);
    }

    public RealText(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public RealText(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.RealText);
        int c = array.getIndexCount();

        for(int i = 0;i< c;i++){
            int attr = array.getIndex(i);
            switch (attr){
                case R.styleable.RealText_duration:
                    duration = array.getInteger(attr,duration);
                    break;
                case R.styleable.RealText_text2:
                    text = array.getString(attr);
                    break;
            }
        }

        array.recycle();
        setAnimationText(text);
    }

    @Override
    public void run() {
        int color = getCurrentTextColor();

        red = Color.red(color);
        green = Color.green(color);
        blue = Color.blue(color);

        ValueAnimator animator = ValueAnimator.ofFloat(0f, 2f);
        animator.setDuration(duration);
        animator.addUpdateListener(this);
        animator.start();

    }


    @Override
    public void onAnimationUpdate(ValueAnimator animation) {
        float value = (float) animation.getAnimatedValue();

        SpannableStringBuilder builder = new SpannableStringBuilder(text);
        for(int i = 0;i<text.length();i++){
            builder.setSpan(new ForegroundColorSpan(Color.argb(clam(value+alphas[i])
                    , red, green, blue)),i,i+1, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
        }
        setText(builder);

    }

    protected int clam(double value){
        return (int)(255*Math.min(Math.max(value, 0f), 1f));
    }

    public void replayAnimation(){
        if(null != text){
            post(this);
        }
    }

    public void setAnimationText(String text){
        this.text = text;
        alphas = new double[text.length()];
        for(int i=0;i<text.length();i++){
            alphas[i] = Math.random() - 1.0f;
        }

        setText(text);
        replayAnimation();
    }
}

3：布局

    <com.widget.RealText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:duration="2000"
        app:text="Hello world"/>