Android 浮动按钮未显示

Question

我尝试用 canvas 制作绘图页，并在角落添加浮动按钮以进行某些操作。但它没有出现。这是我的类

DrawView.java

public class DrawView extends View implements View.OnTouchListener {
private List<Point> points = new ArrayList<>();
private Paint paint = new Paint();

public DrawView(Context c) {
    super(c);
    setFocusable(true);
    setFocusableInTouchMode(true);
    this.setOnTouchListener(this);
    paint.setColor(Color.BLACK);
}

@Override
public void onDraw(Canvas canvas) {
    for (Point point : points) {
        canvas.drawCircle(point.x, point.y, 30, paint);
    }
}

public boolean onTouch(View view, MotionEvent event) {
    Point point = new Point();
    point.x = event.getX();
    point.y = event.getY();
    points.add(point);
    invalidate();
    return true;
}}

和主要 activity

public class DrawingPage extends AppCompatActivity {
private DrawView drawView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_drawing_page);
    drawView = new DrawView(getApplicationContext());
    drawView.setBackgroundColor(Color.WHITE);
    setContentView(drawView);
    drawView.requestFocus();
}}

XML

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="reminder.com.picsartdrawing.DrawingPage">

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/myFAB"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@mipmap/ic_launcher"
        app:elevation="4dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentEnd="true" />
</RelativeLayout>

但是浮动按钮没有出现，有什么解决办法吗？ Screenshot

编辑！！！在 Activity 的 onCreate 方法中，我已经更改了它，现在我已经绘制了带有按钮的 canvas 页面。

RelativeLayout layout = (RelativeLayout) findViewById(R.id.layout);
        drawView = new DrawView(getApplicationContext());
        drawView.setBackgroundColor(Color.WHITE);
        drawView.requestFocus();
        assert layout != null;
        layout.addView(drawView);

Answer 1

在 onCreate() 中，您用 setContentView() 替换了 2 次 "main" 视图，所以只尝试使用此视图：

setContentView(R.layout.activity_drawing_page);

Answer 2

您需要在 activity class 的 onCreate 方法中添加此内容：

FloatingActionButton fab = (FloatingActionButton) findViewById (R.id.fab);
        fab.setOnClickListener (new View.OnClickListener () {
            @Override
            public void onClick (View view) {
                Snackbar.make (view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction ("Action", null).show ();
            }
        });

Android 浮动按钮未显示

Android Floating Button not showing

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