android - view.requestLayout - 以编程方式设置按钮布局

Question

已经有 some solution here关于如何以编程方式更改按钮尺寸

但是，对我有用的是:Here in this site

作者在其中做了这样的事情:

ImageButton someView = (ImageButton)findViewById(R.id.myimage);
someView.requestLayout();
someView.getLayoutParams().width = newWidth;
someView.getLayoutParams().height = newHeight;

现在我只是尝试这样做排除 someView.requestLayout() 并且它仍然有效。 I read the docs about this function但我什么也得不到(我还是个初学者)。这个函数的用途是什么？从长远来看，排除它会造成任何伤害或异常吗？

Answer 1

自行设置宽高不会触发widget的布局。如果您的代码位于 Activity 的 onCreate() 方法中，或者存在触发布局的另一段代码，则已经安排了布局传递，这将是正确的。例如，如果除了设置宽度和高度外，还设置了比例类型，则设置比例类型的方法将触发布局。

来自 ImageView.java

/**
     * Controls how the image should be resized or moved to match the size
     * of this ImageView.
     *
     * @param scaleType The desired scaling mode.
     *
     * @attr ref android.R.styleable#ImageView_scaleType
     */
    public void setScaleType(ScaleType scaleType) {
        if (scaleType == null) {
            throw new NullPointerException();
        }

        if (mScaleType != scaleType) {
            mScaleType = scaleType;

            requestLayout();
            invalidate();
        }
    }

如您所见，如果比例类型已更改，则设置比例类型会触发布局请求。

这是一个测试概念的小应用程序。简而言之，可以在初始布局之前(在 onCreate() 中)、在初始布局完成之后(在 onGlobalLayout() 中)或通过某些用户更改大小 Action (在 onClick() 中)。请参阅代码中有关应用程序工作方式的注释。

MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener,
        ViewTreeObserver.OnGlobalLayoutListener {
    private View theView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        theView = findViewById(R.id.view);
        // If the following line execute, it is before the initial layout pass,
        // so the new width will take effect during that layout pass.
        // Comment and uncomment this line to see the effect.
//        theView.getLayoutParams().width *= 2;

        // Uncomment the following to change size after the initial layout.
        theView.getViewTreeObserver().addOnGlobalLayoutListener(this);
    }

    @Override
    public void onClick(View v) {
//        theView.getLayoutParams().width *= 2;
        // The layout pass has completed since the button is available to click.
        // Here setting the width without requesting a layout will not change the
        // width of the widget - at least not until there is a layout pass requested.
        // Comment and uncomment this line to see the effect.
//        theView.requestLayout();
    }

    @Override
    public void onGlobalLayout() {
        theView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
        theView.getLayoutParams().width *= 2;
        theView.requestLayout();
    }
}

activity_main.xml

<androidx.constraintlayout.widget.ConstraintLayout 
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <View
            android:id="@+id/viewStatic"
            android:layout_width="100dp"
            android:layout_height="50dp"
            android:layout_marginBottom="16dp"
            android:background="@android:color/holo_red_light"
            android:text="Hello World!"
            app:layout_constraintBottom_toTopOf="@+id/view"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_chainStyle="packed" />

        <View
            android:id="@+id/view"
            android:layout_width="100dp"
            android:layout_height="50dp"
            android:background="@android:color/holo_red_light"
            android:text="Hello World!"
            app:layout_constraintBottom_toTopOf="@+id/button"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/viewStatic" />

        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="24dp"
            android:text="Make larger"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/view" />

    </androidx.constraintlayout.widget.ConstraintLayout>