《Android 基础（十）》FloatingActionButton

###介绍

Source Code中的介绍如下：

Floating action buttons are used for a special type of promoted action. They are distinguished
by a circled icon floating above the UI and have special motion behaviors related to morphing,
launching, and the transferring anchor point.

Floating action buttons come in two sizes: the default and the mini. The size can be
controlled with the {@code fabSize} attribute.

As this class descends from {@link ImageView}, you can control the icon which is displayed
via {@link # setImageDrawable(Drawable)}.

The background color of this view defaults to the your theme’s {@code colorAccent}. If you
wish to change this at runtime then you can do so via
{@link # setBackgroundTintList(ColorStateList)}.

@attr ref android.support.design.R.styleable#FloatingActionButton_fabSize

###属性值

属性值	意义
app:backgroundTint	设置背景颜色
app:fabSize	设置FAB的大小，主要有两个取值normal,mini
android:src	设置FAB的图标内容
app:rippleColor	设置FAB点击过程中的颜色
app:elevation	设置FAB正常情况下的阴影效果
app:pressedTranslationZ	设置FAB点击时的阴影大小
app:borderWidth	设置边框宽度
android:clickable	是否可点击true or false
app:layout_anchor	设置FAB的锚点，即以哪个控件为参照点设置位置
app:layout_anchorGravity	设置FAB相对锚点的位置，取值:top,bottom.left,right,center_vertical,fill_vertical, center_horizontal,fill_horizontal,center,fill,clip_vertical,clip_horizontal,start,end

###具体使用
布局文件
activity_main.xml

布局中一共设置了3个FAB，一个在左下角，一个在右下角，一个设置了锚点，颜色可以自己调整，简单的用法就是这个样子，对应的onClick事件在MainActivity中实现。

代码文件
MainActivity.java

package mraz.com.appbardemo;

import android.annotation.TargetApi;
import android.os.Build;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;

public class MainActivity extends AppCompatActivity {

    Toolbar toolbar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
    }


    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public void leftClick(View view) {
        toolbar.setTitle("Left FAB onClick");
    }

    public void rightClick(View view) {
        toolbar.setTitle("Right FAB onClick");
    }

    public void topClick(View view) {
        toolbar.setTitle("Top FAB onClick");
    }
}

###实际效果