Android: align_left对齐到中间

Question

我有一个包含谷歌地图的片段:

<com.google.android.gms.maps.MapView
    android:id="@+id/mapview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    map:cameraZoom="13"
    map:mapType="normal"
    map:uiZoomControls="false"
    map:uiRotateGestures="true"
    map:uiScrollGestures="true"
    map:uiZoomGestures="true"
map:uiTiltGestures="false" />

地图占据了整个屏幕并启用了mylocation:

 map.setMyLocationEnabled(true);

下面的代码应该将mylocation按钮对齐到屏幕的左上角:

 // Get the mylocation button view
                    View locationButton = ((View) mapview.findViewById(Integer.parseInt("1")).getParent()).findViewById(Integer.parseInt("2"));
                RelativeLayout.LayoutParams rlp = (RelativeLayout.LayoutParams) locationButton.getLayoutParams();
                rlp.addRule(RelativeLayout.ALIGN_PARENT_TOP);
                rlp.addRule(RelativeLayout.ALIGN_PARENT_LEFT);

然而，

-这只会将按钮对齐到屏幕的顶部中心。但是，如果我加上:

if (Build.VERSION.SDK_INT >= 17) {
                               rlp.addRule(RelativeLayout.ALIGN_PARENT_START);
                        }

则正确地向左对齐。问题是ALIGN_PARENT_START不能在api 17之前以编程方式使用，我需要从较低的api级别进行支持。为什么不align_parent_left工作在它自己的向左对齐按钮?

Answer 1

这是我移动my location按钮的实现:

<LinearLayout
android:layout_width="match_parent" android:layout_height="match_parent"
android:orientation="vertical">
<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_weight="3">
    <fragment xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/map"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:layout_weight="1"
        android:name="com.google.android.gms.maps.SupportMapFragment">
    </fragment>
      .
      .
      .

On my activity:

mapFragment = ((SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.myMap));
 //if you're using a fragment use:
   //mapFragment = ((SupportMapFragment) getChildFragmentManager() .findFragmentById(R.id.myMap));

    mapFragment.getMapAsync(new OnMapReadyCallback() {
        @Override
        public void onMapReady(GoogleMap googleMap) {
           //add map adjustments here//

           //then this is where you move the my location button
      View locationButton = ((View) mapFragment.getView().findViewById(Integer.parseInt("1")).
            getParent()).findViewById(Integer.parseInt("2"));
    // and next place it, for exemple, on bottom right (as Google Maps app)
    RelativeLayout.LayoutParams rlp = (RelativeLayout.LayoutParams) locationButton.getLayoutParams();
    // position on right bottom
    rlp.addRule(RelativeLayout.ALIGN_PARENT_TOP, 0);
    rlp.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM, RelativeLayout.TRUE);
    rlp.setMargins(0, 0, 30, 30);

        }
    });

Answer 2

不幸的是，有一种方法是从头创建

        RelativeLayout.LayoutParams rlp = new RelativeLayout.LayoutParams((int)(45*density),(int)(45*density));
        rlp.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);
        rlp.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
        rlp.setMargins((int)(5*density), 0, 0, (int)(5*density));
        locationButton.setLayoutParams(rlp);

其中密度为，例如

    DisplayMetrics metrics = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(metrics);
    dispWidth = metrics.widthPixels;
    dispHeight = metrics.heightPixels;
    density = metrics.scaledDensity;