android繼承TextView實現文本彩色閃爍

   閑來無事，收到街邊廣告LED的啟發，想着自己實現一個類似的彩色字體閃爍的效果。

   設計思路

　　　我們知道android的LinearGradient可以實現顏色漸變的背景，那么如果只有速度夠快，通過在水平方向上不斷的平移LinearGradient就可以渲染出文字閃爍的效果了。代碼如下：

package com.example.customview.view;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View.MeasureSpec;
import android.view.WindowManager;
import android.widget.TextView;

public class CustomTextView extends TextView {
    
    private final static String TAG = CirclePercentView.class.getSimpleName();
    private Paint paint1;
    private Paint paint2;
    
    private int mWidth;
    private LinearGradient gradient;
    private Matrix matrix;
    //漸變的速度
    private int deltaX;

    public CustomTextView(Context context) {
        super(context, null);
    }

    public CustomTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView(context, attrs);
        // TODO Auto-generated constructor stub
    }

    private void initView(Context context, AttributeSet attrs) {
        paint1 = new Paint();
        paint1.setColor(getResources().getColor(android.R.color.holo_blue_dark));
        paint1.setStyle(Paint.Style.FILL);

    }

    
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        // TODO Auto-generated method stub
        super.onSizeChanged(w, h, oldw, oldh);
        if(mWidth == 0){
            Log.e(TAG,"*********************");
            mWidth = getMeasuredWidth();
            paint2 = getPaint();
            //顏色漸變器
            gradient = new LinearGradient(0, 0, mWidth, 0, new int[]{Color.BLUE,Color.GREEN,Color.RED}, null, Shader.TileMode.CLAMP);
            paint2.setShader(gradient);
            
            matrix = new Matrix();
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if(matrix !=null){
            deltaX+=mWidth/5;
            if(deltaX>2*mWidth){
                deltaX = -mWidth;
            }
        }
        //關鍵代碼通過矩陣的平移實現
        matrix.setTranslate(deltaX, 0);
        gradient.setLocalMatrix(matrix);
        postInvalidateDelayed(10);
    }
}

運行效果如下：