在 setContentId() 之后将占位符返回到其“空”状态

Posted 2023-03-05

【中文标题】在 setContentId() 之后将占位符返回到其“空”状态

【英文标题】：Return a placeholder to its 'empty' state after setContentId()

【发布时间】：2019-02-17 10:24:34

【问题描述】：

应用 placeholder.setContentID(ImageViewID) 后，我有一个 ImageView 会在屏幕上移动到占位符。

我的问题是如何将 ImageView 重置为其原始位置？理想情况下，这应该将占位符“重置”为空状态。

我尝试过 placeholder.setVisibility(View.GONE) 和 placeholder.setVisibility(View.INVISIBLE)，但它显​​示 没有 反应。我也尝试过 clearAnimation()，但没有成功。

这里是 MainActivity.java

package com.example.stefan.placeholderexperiment;

import android.support.constraint.ConstraintLayout;
import android.support.constraint.Placeholder;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.transition.TransitionManager;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity 
private Placeholder placeholder;
private ConstraintLayout layout;

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

    placeholder = findViewById(R.id.placeholder);
    layout      = findViewById(R.id.layout);


public void transform(View v)
    TransitionManager.beginDelayedTransition(layout);
    placeholder.setContentId(v.getId());

和activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_
    android:layout_
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/image"
        android:onClick="transform"
        android:layout_
        android:layout_
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="16dp"
        android:src="@drawable/ic_android_black_24dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <android.support.constraint.Placeholder
        android:id="@+id/placeholder"
        android:layout_
        android:layout_
        android:layout_marginStart="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.967" />

    </android.support.constraint.ConstraintLayout>

【参考方案1】：

遗憾的是，无法将 ImageView 重置为其原始位置，因为当您调用 Placeholder.setContentID(ImageViewID) 方法时，它会更改 LayoutParams 的 ImageView 并且不会存储先前状态的任何副本。

所以我只能建议你使用两个不同的占位符并轮流改变它们的内容，像这样：

<?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/layout"
                                             android:layout_
                                             android:layout_
                                             tools:context=".MainActivity">

    <ImageView
        android:id="@+id/image"
        android:layout_
        android:layout_
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="16dp"
        android:onClick="transform"
        android:src="@drawable/unnamed"/>

    <android.support.constraint.Placeholder
        android:id="@+id/placeholder_top"
        android:layout_
        android:layout_
        android:layout_marginStart="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

    <android.support.constraint.Placeholder
        android:id="@+id/placeholder_bottom"
        android:layout_
        android:layout_
        android:layout_marginStart="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.967"/>

</android.support.constraint.ConstraintLayout>


public class MainActivity extends AppCompatActivity 

    private Placeholder placeholderTop;
    private Placeholder placeholderBottom;
    private ConstraintLayout layout;

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

        placeholderTop = (Placeholder) findViewById(R.id.placeholder_top);
        placeholderBottom = (Placeholder) findViewById(R.id.placeholder_bottom);
        layout = (ConstraintLayout) findViewById(R.id.layout);
        placeholderTop.setContentId(R.id.image);
    

    public void transform(View v) 
        if (placeholderTop.getContent() == null) 
            TransitionManager.beginDelayedTransition(layout);
            placeholderTop.setContentId(v.getId());
            placeholderBottom.setContentId(-1);
         else if (placeholderBottom.getContent() == null) 
            TransitionManager.beginDelayedTransition(layout);
            placeholderBottom.setContentId(v.getId());
            placeholderTop.setContentId(-1);
        
    

【讨论】：

这很完美！谢谢你。我很惊讶 placeholderTop.setContentId(-1);不会造成任何问题...

一个更好的写法是View.NO_ID。现在有意义吗？