Android | 实用代码片段(3)

• 在 View Layout 完成后获取 控件大小

final TextView tv = (TextView) findViewById(R.id.myTextView);
ViewTreeObserver vto = tv.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        Toast.makeText(MyActivity.this, tv.getWidth() + " x " + tv.getHeight(), Toast.LENGTH_LONG).show();
        tv.getViewTreeObserver().removeGlobalOnLayoutListener(this);
    }
});

• 关键帧插值器

public static float calculateValue(float[] values, float time, float def) {
    	float value = def;
        if (values != null && values.length > 0) {
            float segment = 1.0f / (float)(values.length - 1);
            int index = (int)(time / segment);
            if (index >= values.length - 1) {
            	value = values[values.length - 1];
            } else {
            	float extra = time - segment * (float)index;
            	value = values[index] + (values[index + 1] - values[index]) * extra / segment;
            }
        }
    return value;
}

• 给图片叠加渐变

private void addShadow(Bitmap bitmap, int color) {
    int[] colors = new int[]{
            color & 0x00FFFFFF,
            color & 0x0AFFFFFF,
            color & 0x33FFFFFF,
            color & 0x66FFFFFF,
            color & 0x99FFFFFF,
            color & 0xCCFFFFFF,
            color
    };
    GradientDrawable gradientDrawable = new GradientDrawable(GradientDrawable.Orientation.TOP_BOTTOM, colors);
    gradientDrawable.setGradientType(GradientDrawable.LINEAR_GRADIENT);
    Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
    gradientDrawable.setBounds(rect);
    gradientDrawable.setLevel(8);
    Canvas canvass = new Canvas(bitmap);
    gradientDrawable.draw(canvass);
}

• ListView 或者 GridView 去除滑动特性 (即固定高度)

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    heightMeasureSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2, MeasureSpec.AT_MOST);
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}

• 获取系统长按时间，自定义 View 会用到

getSystemLongPressTime

• 判断设备是否有网

public static boolean isOnline(Context context) {
    ConnectivityManager connMgr = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
    return (networkInfo != null && networkInfo.isConnected());
}