Question

我有一个问题，我在视图寻呼机内有一个表面视图。一切都很好，直到我按下其中一个标签。视图寻呼机滚动，但下一个屏幕上的页面被压扁。

如果我退出应用程序并返回其中，第二页将呈现正常。然后，如果我按回到第一个，它会再次压扁。

我根本不知道布局的哪个部分出错了，据我所知，表面视图的实际高度没有变化，就像我使用.getHeight（）方法一样在表面视图上，它总是返回相同的值。

这是我的查看分页器类：

public class PendulumViewPager extends ViewPager {


public PendulumViewPager(Context context) {
    super(context);
}

public PendulumViewPager(Context context, AttributeSet attrs) {
    super(context, attrs);
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    return false;
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    return false;
}

以下是添加到视图寻呼机的片段：

public class SurfacePanelFragment extends Fragment{

private int TYPE = 1;
private SurfacePanel panel;
public void setType(int type){
    TYPE = type;
}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_surface_panel, container, false);

    panel = view.findViewById(R.id.canvas);
    panel.setType(TYPE);
    return view;
}

public void startStopPendulum(ImageButton view){
    panel.startStop(view);
}

public void stopPendulum(){
    panel.stop();
}

@Override
public void onResume() {
    if(getUserVisibleHint()) {
        panel.delayStartThread();
        ((MainActivity)getActivity()).getStopButton().setImageDrawable(getContext().getResources().getDrawable(R.drawable.ic_pause_white_48dp));
    }
    super.onResume();
}

@Override
public void onPause() {
    panel.terminate();
    super.onPause();
}

public void stopRendering(){
    panel.stopRendering();
}

public void startRendering(){
    panel.startRendering();
}

@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if(panel != null) {
        if (isVisibleToUser) {
            panel.delayStartThread();
            ((MainActivity)getActivity()).getStopButton().setImageDrawable(getContext().getResources().getDrawable(R.drawable.ic_pause_white_48dp));
            Log.i("WP", String.valueOf(panel.getHeight()));
        } else {
            panel.terminate();
        }
    }
}

以下是主要活动：

public class MainActivity extends AppCompatActivity {

private PendulumViewPager pager;
private ArrayList<SurfacePanelFragment> fragments = new ArrayList<SurfacePanelFragment>(2);

private ImageButton stopButton;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayShowTitleEnabled(false);

    pager = findViewById(R.id.view_pager);
    pager.setAdapter(new FragmentStatePagerAdapter(getSupportFragmentManager()) {
        @Override
        public Fragment getItem(int position) {
            SurfacePanelFragment frag = new SurfacePanelFragment();
            switch (position) {
                case 0:
                    frag.setType(SurfacePanel.SINGLE_PENDULUM);

                    fragments.add(0, frag);
                    return frag;
                case 1:
                    frag.setType(SurfacePanel.DOUBLE_PENDULUM);
                    fragments.add(1, frag);
                    return frag;
                default:
                    return null;
            }
        }

        @Override
        public int getCount() {
            return 2;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            switch (position){
                case 0: return "Single";
                case 1: return "Double";
                default: return "";
            }
        }
    });

    TabLayout pagerTabs = findViewById(R.id.pager_tabs);
    pagerTabs.setTabGravity(TabLayout.GRAVITY_FILL);
    pagerTabs.setupWithViewPager(pager);

    stopButton = findViewById(R.id.stop_button);
    stopButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            startStopCurrentPendulum((ImageButton) view);
        }
    });

    ImageButton helpButton = findViewById(R.id.help_button);
    helpButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            startHelpActivity();
        }
    });
}

private void startStopCurrentPendulum(ImageButton view) {
    fragments.get(pager.getCurrentItem()).startStopPendulum(view);
}

public ImageButton getStopButton(){
    return stopButton;
}

private void startHelpActivity(){
    Intent intent = new Intent(this, HelpActivity.class);
    startActivity(intent);
}

这是SurfacePanel类

public class SurfacePanel extends SurfaceView implements SurfaceHolder.Callback {

public static final int SINGLE_PENDULUM = 1;
public static final int DOUBLE_PENDULUM = 2;

private int TYPE = 1;

private PendulumThread _thread;
private boolean needToStartThread = false;

private SurfaceHolder holder;

public SurfacePanel(Context context, AttributeSet attrSet) {
    super(context, attrSet);
    SurfaceHolder holder = getHolder();
    holder.addCallback(this);
}


@Override
public void surfaceCreated(SurfaceHolder surfaceHolder) {
    Log.i("WP", String.valueOf(this.getHeight()));
    this.holder = surfaceHolder;
    if(needToStartThread){
        startThread();
        needToStartThread = false;
    }
}

@Override
public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {

}

@Override
public void surfaceDestroyed(SurfaceHolder surfaceHolder) {
    if(_thread != null) {
        try {
            _thread.terminate();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    this.holder = null;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    if (_thread != null) {
        if (event.getAction() == MotionEvent.ACTION_DOWN) {
            _thread.click(event);
        } else if (event.getAction() == MotionEvent.ACTION_MOVE) {
            _thread.updatePos(event);
        } else if (event.getAction() == MotionEvent.ACTION_UP) {
            _thread.unclick();
        }
    }
    return true;
}

public void startStop(ImageView button) {
    if(_thread != null){
        if(_thread.isPRunning()){
            button.setImageDrawable(getContext().getResources().getDrawable(R.drawable.ic_play_arrow_white_48dp));
            _thread.pStop();
        }else{
            button.setImageDrawable(getContext().getResources().getDrawable(R.drawable.ic_pause_white_48dp));
            _thread.pStart();
        }
    }
}

public void start(){
    if(_thread != null){
        _thread.pStart();
    }
}

public void stop(){
    if(_thread != null){
        _thread.pStop();
    }
}

public void stopRendering(){
    if(_thread != null){
        Log.i("WP", "A");
        _thread.stopRendering();
    }
}

public void startRendering(){
    if(_thread != null){
        Log.i("WP", "D");
        _thread.startRendering();
    }
}

public void terminate(){
    if(_thread != null){
        try {
            _thread.terminate();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

private void startThread(){
    if(_thread == null || !_thread.isAlive()) {
        switch (TYPE) {
            case SurfacePanel.SINGLE_PENDULUM:
                _thread = new SinglePendulumThread(holder, getWidth(), getHeight(), getContext());
                _thread.pStart();
                _thread.start();
                break;
            case SurfacePanel.DOUBLE_PENDULUM:
                _thread = new DoublePendulumThread(holder, getWidth(), getHeight(), getContext());
                _thread.pStart();
                _thread.start();
                break;
            default:
                _thread = new SinglePendulumThread(holder, getWidth(), getHeight(), getContext());
                _thread.pStart();
                _thread.start();
                break;
        }
    }
}

public void delayStartThread(){
    if(holder == null) {
        needToStartThread = true;
    }else{
        startThread();
    }
}

public void setType(int type){
    TYPE = type;
}

这是表面面板片段，其中有表面面板视图

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<com.astarphysics.wikidpendulum.SurfacePanel
    android:id="@+id/canvas"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:layout_editor_absoluteX="8dp"
    tools:layout_editor_absoluteY="8dp" />
</RelativeLayout>

这是单摆线程

public class SinglePendulumThread extends PendulumThread{

private SurfaceHolder holder;
private Paint paint;
private int backgroundColor;
private int width;
private Context context;

private boolean clicked = false;

private static final double g = 9.81;
private final int RADIUS;

private int length;
private double theta = Math.PI/8;
private double thetaV = 0;

SinglePendulumThread(SurfaceHolder holder, int width, int height, Context context){
    this.holder = holder;
    this.context = context;

    int bobColor = context.getResources().getColor(R.color.colorBob);
    int shadowColor = context.getResources().getColor(R.color.shadowColor);
    backgroundColor = context.getResources().getColor(R.color.backgroundColor);
    paint = new Paint();
    paint.setColor(bobColor);
    paint.setShadowLayer(5, -1, 2, shadowColor);

    this.width = width;
    RADIUS = dpToPx(20);
    length = dpToPx(200);
}

protected void update(){
    if(pRunning && !clicked) {
        thetaV += (-1 * g * Math.sin(theta)) / length;
        theta += thetaV * (40 * Math.pow(10, -2));
    }
}

protected void render(){
    Canvas canvas = holder.lockCanvas();
    canvas.drawColor(backgroundColor);

    canvas.drawLine(width / 2, 0, (float) ((width / 2) + (length * Math.sin(theta))), (float) (length * Math.cos(theta)), paint);
    canvas.drawCircle((int) Math.round((width / 2) + (length * Math.sin(theta))), (int) Math.round(length * Math.cos(theta)), RADIUS, paint);

    holder.unlockCanvasAndPost(canvas);
}

@Override
void click(MotionEvent e) {
    clicked = true;
    updatePos(e);
}

@Override
void updatePos(MotionEvent e){
    length = (int)Math.round(Math.sqrt((Math.abs(e.getX()-(width/2))*Math.abs(e.getX()-(width/2)))+(e.getY()*e.getY())));
    theta = Integer.signum(Math.round((e.getX()-(width/2))))*Math.asin((Math.abs(e.getX()-(width/2))/length));
}

@Override
void unclick() {
    this.resetForPStart();
    clicked = false;
}

private void resetForPStart(){
    thetaV = 0;
}

private int dpToPx(int dp) {
    DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
    return Math.round(dp * (displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT));
}

这是双摆线：

public class DoublePendulumThread extends PendulumThread {

private SurfaceHolder holder;
private Paint paint;
private int backgroundColor;
private int width;
private int height;
private Context context;

private boolean clicked1 = false;
private boolean clicked2 = false;

private final int RADIUS;
private final double m1 = 3;
private final double m2 = 3;
private static final double g = 9.81;

private double l1;
private double l2;

private double[] state = new double[4];
private double[] dydt = new double[4];
private double[] prev = new double[4];
private double[] midpt = new double[4];
private static final double h = 0.5;
private static final double DIMENSION = 4;
private static final double HALF = h/2;
private static final double THIRD = h/3;
private static final double SIXTH = h/6;


DoublePendulumThread(SurfaceHolder holder, int width, int height, Context context){
    this.holder = holder;
    this.context = context;
    this.width = width;
    this.height = height;

    //Setting sizes that require Context to be set
    RADIUS = dpToPx(20);
    l1 = dpToPx(150);
    l2 = dpToPx(150);
    state[0] = Math.PI/8;

    //Setting up paints for rendering on Canvas
    int bobColor = context.getResources().getColor(R.color.colorBob);
    int shadowColor = context.getResources().getColor(R.color.shadowColor);
    backgroundColor = context.getResources().getColor(R.color.backgroundColor);
    paint = new Paint();
    paint.setColor(bobColor);
    paint.setShadowLayer(5, -1, 2, shadowColor);
}

/*
Evaluates derivatives for Runge-Kutta.
*/
private void loadDys(double[] y){
    dydt[0] = y[2]; //Theta1
    dydt[1] = y[3]; //Theta2

    dydt[2] = ( -1*g*(2*m1 + m2)*sin(y[0]) - m2*g*sin(y[0] - 2*y[1]) - 2*sin(y[0] - y[1])*m2*(y[3]*y[3]*l2 + y[2]*y[2]*l1*cos(y[0] - y[1])) ) / (l1*(2*m1 + m2 - m2*cos(2*y[0]-2*y[1])));
    dydt[3] = (2*sin(y[0] - y[1])*(y[2]*y[2]*l1*(m1+m2) + g*(m1+m2)*cos(y[0]) + y[3]*y[3]*l2*m2*cos(y[0]-y[1]))) / (l2*(2*m1 + m2 - m2*cos(2*y[0]-2*y[1])));
}

/*
Each time update is run one iteration of the Runge-Kutta method takes place, with time step h.
*/
protected void update(){
    if(pRunning && !clicked1 && !clicked2) {
        for (int i = 0; i < DIMENSION; i++) {
            midpt[i] = state[i];
            prev[i] = state[i];
        }

        loadDys(midpt);
        for (int i = 0; i < DIMENSION; i++) {
            state[i] += SIXTH * dydt[i];
            midpt[i] = prev[i] + HALF * dydt[i];
        }
        loadDys(midpt);
        for (int i = 0; i < DIMENSION; i++) {
            state[i] += THIRD * dydt[i];
            midpt[i] = prev[i] + HALF * dydt[i];
        }
        loadDys(midpt);
        for (int i = 0; i < DIMENSION; i++) {
            state[i] += THIRD * dydt[i];
            midpt[i] = prev[i] + h * dydt[i];
        }
        loadDys(midpt);
        for (int i = 0; i < DIMENSION; i++) {
            state[i] += SIXTH * dydt[i];
        }
    }else if(pRunning && clicked1) {
        state[3] += (-1 * g * Math.sin(state[1])) / l2;
        state[3] = state[3] * 0.9;
        state[1] += state[3] * (40 * Math.pow(10, -2));
    }
}

protected void render(){
    Canvas canvas = holder.lockCanvas();
    canvas.drawColor(backgroundColor);

    canvas.drawLine(width / 2, height/4, (float) ((width / 2) + (l1 * Math.sin(state[0]))), (float) (height/4 + l1 * Math.cos(state[0])), paint);
    canvas.drawLine((float) ((width / 2) + (l1 * Math.sin(state[0]))), (float) (height/4 + l1 * Math.cos(state[0])), (float) ((width / 2) + (l1 * Math.sin(state[0])) + (l2 * Math.sin(state[1]))), (float) (height/4 + l1 * Math.cos(state[0]) + l2 * Math.cos(state[1])), paint);
    canvas.drawCircle((float) ((width / 2) + (l1 * Math.sin(state[0]))), (float) (height/4 + l1 * Math.cos(state[0])), RADIUS, paint);
    canvas.drawCircle((float) ((width / 2) + (l1 * Math.sin(state[0])) + (l2 * Math.sin(state[1]))), (float) (height/4 + l1 * Math.cos(state[0]) + l2 * Math.cos(state[1])), RADIUS, paint);

    holder.unlockCanvasAndPost(canvas);
}

void updatePos(MotionEvent e){
    if(clicked1){
        l1 = (int)Math.round(Math.sqrt(((e.getX()-(width/2))*(e.getX()-(width/2)))+((e.getY()-height/4)*(e.getY()-height/4))));
        if(e.getY() - height/4 < 0) {
            if (Math.round(e.getX() - width / 2) == 0) {
                state[0] = Math.PI;
            } else {
                state[0] = Integer.signum(Math.round((e.getX() - (width / 2)))) * Math.acos((Math.abs(e.getX() - (width / 2)) / l1)) + Integer.signum(Math.round((e.getX() - (width / 2)))) * Math.PI / 2;
            }
        }else if(Math.round(e.getY() - (height/4)) == 0){
            state[0] = Integer.signum(Math.round(e.getX() - (width/2))) * Math.PI / 2;
        }else{
            state[0] = Math.asin((e.getX()-(width/2))/l1);
        }
    }else if(clicked2){
        l2 = (int)Math.round(Math.sqrt(((e.getX()-((width / 2) + (l1 * Math.sin(state[0]))))*(e.getX()-((width / 2) + (l1 * Math.sin(state[0])))))+((e.getY()-(height/4 + l1 * Math.cos(state[0])))*(e.getY()-(height/4 + l1 * Math.cos(state[0]))))));
        if(e.getY() - (height/4 + l1 * Math.cos(state[0])) < 0){
            if(Math.round(e.getX() - ((width/2) + l1*sin(state[0]))) == 0){
                state[1] = Math.PI;
            }else {
                state[1] = Integer.signum((int) Math.round((e.getX() - ((width / 2) + (l1 * Math.sin(state[0])))))) * Math.acos((Math.abs(e.getX() - ((width / 2) + (l1 * Math.sin(state[0])))) / l2)) + Integer.signum((int) Math.round((e.getX() - ((width / 2) + (l1 * Math.sin(state[0])))))) * Math.PI / 2;
            }
        }else if(Math.round(e.getY() - (height/4 + l1 * Math.cos(state[0]))) == 0) {
            state[1] = Integer.signum((int) Math.round(e.getX() - ((width/2) + l1*sin(state[0])))) * Math.PI / 2;
        }else{
            state[1] = Math.asin((e.getX()-((width / 2) + (l1 * Math.sin(state[0]))))/l2);
        }
    }
}

void click(MotionEvent e){
    if((e.getX() - ((width / 2) + (l1 * Math.sin(state[0])) + (l2 * Math.sin(state[1]))))*(e.getX() - ((width / 2) + (l1 * Math.sin(state[0])) + (l2 * Math.sin(state[1])))) + (e.getY() - (height/4 + l1 * Math.cos(state[0]) + l2 * Math.cos(state[1])))*(e.getY() - (height/4 + l1 * Math.cos(state[0]) + l2 * Math.cos(state[1]))) <= RADIUS*RADIUS){
        clicked2 = true;
    }else {
        clicked1 = true;
    }
    updatePos(e);
}

void unclick(){
    if(clicked1 || clicked2) {
        state[2] = 0;
        state[3] = 0;
        for (int i = 0; i < DIMENSION; i++) {
            dydt[i] = 0;
            midpt[i] = 0;
            prev[i] = 0;
        }
        clicked1 = false;
        clicked2 = false;
    }
}

private int dpToPx(int dp) {
    DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
    return Math.round(dp * (displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT));
}

private static double sin(double x){
    return Math.sin(x);
}
private static double cos(double x){
    return Math.cos(x);
}

以下是将片段嵌入到视图寻呼机中的主要活动。

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/.   apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.astarphysics.wikidpendulum.MainActivity"
>

<android.support.constraint.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior">

    <com.astarphysics.wikidpendulum.PendulumViewPager
        android:id="@+id/view_pager"
        android:layout_width="0dp"
        android:layout_height="0dp"
        tools:layout_constraintTop_creator="1"
        tools:layout_constraintRight_creator="1"
        tools:layout_constraintBottom_creator="1"
        android:layout_marginStart="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        android:layout_marginEnd="8dp"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginTop="8dp"
        tools:layout_constraintLeft_creator="1"
        android:layout_marginBottom="8dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp">

    </com.astarphysics.wikidpendulum.PendulumViewPager>
</android.support.constraint.ConstraintLayout>

<android.support.design.widget.AppBarLayout
android:layout_height="wrap_content"
android:layout_width="match_parent">

    <android.support.v7.widget.Toolbar
        app:layout_scrollFlags="enterAlways"
        android:id="@+id/toolbar"
        android:layout_height="192dp"
        android:layout_width="match_parent"
        app:contentInsetLeft="0dp"
        app:contentInsetStart="0dp">
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <RelativeLayout
                android:layout_width="match_parent"
                android:layout_height="144dp">
                <LinearLayout
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_alignParentEnd="true"
                    android:layout_alignParentRight="true"
                    android:padding="10dp">

                <android.support.v7.widget.AppCompatImageButton
                    android:id="@+id/stop_button"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    app:srcCompat="@drawable/ic_pause_white_48dp"
                    android:background="?attr/selectableItemBackgroundBorderless"
                    android:layout_marginRight="10dp"
                    android:layout_marginEnd="10dp"/>

                <android.support.v7.widget.AppCompatImageButton
                    android:id="@+id/help_button"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    app:srcCompat="@drawable/ic_help_white_48dp"
                    android:background="?attr/selectableItemBackgroundBorderless" />

                </LinearLayout>

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="center"
                    android:orientation="vertical">

                    <ImageView
                        android:layout_width="80dp"
                        android:layout_height="80dp"
                        android:src="@drawable/icon"/>

                    <TextView
                        android:layout_width="150dp"
                        android:layout_height="wrap_content"
                        android:text="@string/app_name"
                        android:gravity="center"
                        android:textSize="24sp"
                        android:fontFamily="sans-serif-smallcaps"
                        android:textColor="@color/textColor"/>

                </LinearLayout>
            </RelativeLayout>

            <android.support.design.widget.TabLayout
                android:id="@+id/pager_tabs"
                android:layout_width="match_parent"
                android:layout_height="48dp">

            </android.support.design.widget.TabLayout>

        </LinearLayout>
    </android.support.v7.widget.Toolbar>
</android.support.design.widget.AppBarLayout>


</android.support.design.widget.CoordinatorLayout>

如果您认为它是其他内容，那么我可以添加代码。

感谢。

Answer 1

简单地更改ViewPager中的页面不会强制片段经历其生命周期或导致重新创建SurfaceView。点击recents或home然后返回应用会导致重新创建SurfaceView，这似乎可以解决您所看到的问题。

如果问题是与您的布局相关的微妙问题，我建议您尽可能简化它。我已经重新设计了两个主要布局以简化它们，如下所示。如果您决定走这条路线，您可能需要在主布局中更改一些内容以获得您想要的尺寸/位置。你不应该做任何结构性的改变。

如果上述方法不起作用，还要尝试的其他方法是在为API 26+选择片段时强制重新创建片段。这将强制重新实例化片段和布局，并应纠正问题。

如果新布局有效，那将是最好的;如果你必须在选项卡选择时重新创建，那只是一个解决方法。如果您发现了潜在的问题，请在此处发布。我很想知道它是什么。也许这个问题的另一位读者可以深究它。

<强> pendulum_layout.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="144dp"
        app:contentInsetLeft="0dp"
        app:contentInsetStart="0dp">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentEnd="true"
                android:layout_alignParentRight="true"
                android:padding="10dp">

                <android.support.v7.widget.AppCompatImageButton
                    android:id="@+id/stop_button"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    android:layout_marginEnd="10dp"
                    android:layout_marginRight="10dp"
                    android:background="?attr/selectableItemBackgroundBorderless"
                    app:srcCompat="@drawable/ic_pause_white_48dp" />

                <android.support.v7.widget.AppCompatImageButton
                    android:id="@+id/help_button"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    android:background="?attr/selectableItemBackgroundBorderless"
                    app:srcCompat="@drawable/ic_help_white_48dp" />

            </LinearLayout>

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:gravity="center"
                android:orientation="vertical">

                <ImageView
                    android:layout_width="80dp"
                    android:layout_height="80dp"
                    android:src="@drawable/icon" />

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:fontFamily="sans-serif-smallcaps"
                    android:gravity="center"
                    android:text="@string/app_name"
                    android:textColor="#FF000000"
                    android:textSize="24sp" />

            </LinearLayout>
        </RelativeLayout>
    </android.support.v7.widget.Toolbar>

    <com.example.viewpagerbase.PendulumViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.design.widget.TabLayout
            android:id="@+id/pager_tabs"
            android:layout_width="match_parent"
            android:layout_height="48dp" />
    </com.example.viewpagerbase.PendulumViewPager>
</LinearLayout>

<强> fragment_main.xml

    <com.example.viewpagerbase.MySurfaceView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/surfaceView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

这是在选择时强制新片段的一种方法。如果您搜索它们，还可以在线使用其他方法。

将以下内容添加到ViewPager并从每个构造函数调用。这将为API 26+设置页面侦听器。只要选择了不同的页面，该侦听器就会触发。

private void init() {
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
        return;
    }
    addOnPageChangeListener(new OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        }

        @Override
        public void onPageSelected(int position) {
            MainActivity.SectionsPagerAdapter adapter =
                // Your adapter name goes here
                ((MainActivity.SectionsPagerAdapter) getAdapter());
            adapter.invalidateFragment(position);
        }

        @Override
        public void onPageScrollStateChanged(int position) {
        }
    });
}

将以下内容添加到适配器：

private List<SurfacePanelFragment> fragments = new ArrayList<>(PAGE_COUNT);

    @Override
    public SurfacePanelFragment getItem(int position) {
        if (fragments.get(position) == null) {
            fragments.set(position, SurfacePanelFragment.newInstance());
        }
        return fragments.get(position);
    }

    @Override
    public int getItemPosition(Object object) {
        return (fragments.contains(object)) ? POSITION_UNCHANGED : POSITION_NONE;
    }

    public void invalidateFragment(int position) {
        fragments.set(position, null);
        notifyDataSetChanged();
    }

    private static final int PAGE_COUNT = 2;

Surface View压缩在视图寻呼机内部

1 个答案: