android – 按钮的随机大小和位置:意外行为

我的约束布局:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    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:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginTop="0dp"
        android:layout_marginEnd="0dp"
        android:layout_marginBottom="0dp"
        android:minWidth="0dp"
        android:minHeight="0dp"
        android:text="@string/start"
        android:visibility="visible"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

我的简化代码:

import android.annotation.SuppressLint;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;

import java.util.Random;


public class MainActivity extends AppCompatActivity {

    final Random rand = new Random();

    private Button btn;
    private float widthPixels, heightPixels;
    private float minBtnSize, maxBtnSize;


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

        /* Obtaining screen's display properties. */
        final DisplayMetrics displaymetrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
        widthPixels = displaymetrics.widthPixels;
        heightPixels = displaymetrics.heightPixels; // includes BotNavBar
        heightPixels -= 162; // size of the "Virtual Nav Bar" at the bottom
        float minDim = Math.min(widthPixels, heightPixels);
        minBtnSize = minDim/25;
        maxBtnSize = minDim/2;


        /* Setting up the experiment's Button*/
        btn = findViewById(R.id.btn);
        btn.setOnTouchListener(new View.OnTouchListener(){
            public boolean onTouch(View view, MotionEvent event){

                /* Touch Events. */
                switch (event.getAction()) {

                    case MotionEvent.ACTION_UP:                            
                        /* Move and resize the button. */
                        launchNewAttempt(x, y);
                        break;

                    default:
                        break;
                }
                return true;
            }
        });

        /* Setting up the beginning Button's state. */
        init();
    }


    /**
     * Initializing the Button shown at the very beginning.
     */
    private void init() {
        btn.setX(0);
        btn.setY(0);
        btn.setWidth((int)widthPixels);
        btn.setHeight((int)heightPixels);
    }


    /**
     * Called whenever the user releases the experiment's button (pressed "UP").
     */
    private void launchNewAttempt() {

        /* Random size for the "new" button. */
        int size=(int)(minBtnSize+(maxBtnSize-minBtnSize)*rand.nextDouble());
        btn.setWidth(size);
        btn.setHeight(size);

        /* Random position for the "new" button. */
        float dx = rand.nextFloat() * (widthPixels - size);
        float dy = rand.nextFloat() * (heightPixels - size);
        btn.setX(dx);
        btn.setY(dy);
    }
}

预期行为:

填充整个屏幕的按钮出现在开头.按下后,相同的按钮被调整大小(正方形,边长至少为屏幕宽度的1/25,最多为屏幕宽度的1/2),并在屏幕上随机移动.每次用户再次按下该按钮时,其行为方式相同(新的随机位置和大小).

我的问题:

btn.setX()和btn.setY()似乎没有按预期运行.我原以为他们会在屏幕上确定按钮的绝对位置,但是对于init()使用以下示例代码有一个奇怪的行为:

btn.setX(0);
btn.setY(0);
btn.setWidth(150);
btn.setHeight(150);

大小似乎没问题,但位置似乎是相对于屏幕中间的(虽然它似乎也取决于按钮的大小,因为使用前面介绍的代码它正确填充整个屏幕).我希望这个位置相对于屏幕的左上角(不包括顶部的ActionBar / TitleBar,也不包括底部的NavigationBar).

当我运行当前代码时,按钮实际上有时会在屏幕外关闭.这有什么不对?

最佳答案 我尝试用LinearLayout替换布局的根节点代码并且它正常工作,这意味着问题与ContraintLayout的内部逻辑有关.知道我试图改变按钮的位置,考虑约束而不是绝对位置,特别是关于按钮的顶部和起始边距.因此,launchNewAttempt()方法可以类似于:

private void launchNewAttempt() {
    final int size = (int) (minBtnSize + (maxBtnSize - minBtnSize) * rand.nextDouble());
    final int left = (int) (rand.nextFloat() * (widthPixels - size));
    final int top = (int) (rand.nextFloat() * (heightPixels - size));
    final ConstraintLayout.LayoutParams layoutParams = (ConstraintLayout.LayoutParams) btn.getLayoutParams();

    layoutParams.width = size;
    layoutParams.height = size;
    layoutParams.leftMargin = left;
    layoutParams.topMargin = top;

    btn.setLayoutParams(layoutParams);
}

我还只保留了两个约束,将按钮放在布局中,并删除了底部和底部的按钮:

<Button
    android:id="@+id/btn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="0dp"
    android:layout_marginTop="0dp"
    android:layout_marginEnd="0dp"
    android:layout_marginBottom="0dp"
    android:minWidth="0dp"
    android:minHeight="0dp"
    android:text="Start"
    android:visibility="visible"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

希望这对你有用.

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