<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@mipmap/test">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:orientation="horizontal">

        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="請(qǐng)輸入..." />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="提交" />
    </LinearLayout>

</RelativeLayout>

   <com.myapplication.MyBackground
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@mipmap/test" />

public class MyBackground extends RelativeLayout {
    private Context mContext;
    public MyBackground(Context context) {
        super(context);
        mContext = context;
    }

    public MyBackground(Context context, AttributeSet attrs) {
        super(context, attrs);
        mContext = context;
    }

    public MyBackground(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        mContext = context;
    }

    public MyBackground(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        mContext = context;
    }

    @Override

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        DisplayMetrics dm = new DisplayMetrics();
        WindowManager mWm = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
        mWm.getDefaultDisplay().getMetrics(dm);
        int screenHeight = dm.heightPixels;
        heightMeasureSpec = MeasureSpec.makeMeasureSpec(screenHeight, MeasureSpec.EXACTLY);
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }
}