DrawerLayout全屏滑动

注：DrawerLayout自带的滑动范围默认只有20dp

下面方法通过反射机制解决了此问题

/**
 * 抽屉滑动范围控制
 * @param activity
 * @param drawerLayout
 * @param displayWidthPercentage 占全屏的份额0~1
 */
private void setDrawerLeftEdgeSize(Activity activity, DrawerLayout drawerLayout, float displayWidthPercentage) {
    if (activity == null || drawerLayout == null)
        return;
    try {
        // find ViewDragHelper and set it accessible
        Field leftDraggerField = drawerLayout.getClass().getDeclaredField("mLeftDragger");
        leftDraggerField.setAccessible(true);
        ViewDragHelper leftDragger = (ViewDragHelper) leftDraggerField.get(drawerLayout);
        // find edgesize and set is accessible
        Field edgeSizeField = leftDragger.getClass().getDeclaredField("mEdgeSize");
        edgeSizeField.setAccessible(true);
        int edgeSize = edgeSizeField.getInt(leftDragger);
        // set new edgesize
        // Point displaySize = new Point();
        DisplayMetrics dm = new DisplayMetrics();
        activity.getWindowManager().getDefaultDisplay().getMetrics(dm);
        edgeSizeField.setInt(leftDragger, Math.max(edgeSize, (int) (dm.widthPixels * displayWidthPercentage)));
    } catch (NoSuchFieldException e) {
        Log.e("NoSuchFieldException", e.getMessage().toString());
    } catch (IllegalArgumentException e) {
        Log.e("IllegalArgumentException", e.getMessage().toString());
    } catch (IllegalAccessException e) {
        Log.e("IllegalAccessException", e.getMessage().toString());
    }
}

使用时只要调用此方法就行

setDrawerLeftEdgeSize(this, mDrawerLayout, 0.6f);

===========================================分割线====================================

当使用的DrawerLayout是自定义控件时出现的问题

Field leftDraggerField = drawerLayout.getClass().getDeclaredField("mLeftDragger");

这里会抛出NoSuchFieldException异常，原因是mLeftDragger变量是在DrawerLayout类里面定义的，在自定义的类中并没有定义。

解决方法：改为获取自定义类的父类也即DrawerLayout类中的mLeftDragger即可，替换如下

Field leftDraggerField = getDeclaredField(drawerLayout, "mLeftDragger");

/**
* 循环向上转型, 获取对象的 DeclaredField
*
 * @param object    : 子类对象
* @param fieldName : 父类中的属性名
* @return 父类中的属性对象
*/
public Field getDeclaredField(Object object, String fieldName) {
    Field field = null;

    Class<?> clazz = object.getClass();

    for (; clazz != Object.class; clazz = clazz.getSuperclass()) {
        try {
            field = clazz.getDeclaredField(fieldName);
            return field;
        } catch (Exception e) {
            //这里甚么都不要做！并且这里的异常必须这样写，不能抛出去。
            //如果这里的异常打印或者往外抛，则就不会执行clazz = clazz.getSuperclass(),最后就不会进入到父类中了
        }
    }

    return null;
}