java - 在 setContentId() 之后将占位符返回到其 'empty' 状态

Question

我有一个 ImageView，一旦我应用了 placeholder.setContentID(ImageViewID)，它就会在屏幕上移动到占位符。

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

我已经尝试了 placeholder.setVisibility(View.GONE) 和 placeholder.setVisibility(View.INVISIBLE)，但显示没有 react 。我还尝试了 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_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/image"
        android:onClick="transform"
        android:layout_width="24dp"
        android:layout_height="24dp"
        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_width="24dp"
        android:layout_height="24dp"
        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>

Answer 1

不幸的是，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 的 LayoutParams ImageView 并且不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更改它们的内容，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_width="match_parent"
                                             android:layout_height="match_parent"
                                             tools:context=".MainActivity">

    <ImageView
        android:id="@+id/image"
        android:layout_width="24dp"
        android:layout_height="24dp"
        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_width="24dp"
        android:layout_height="24dp"
        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_width="24dp"
        android:layout_height="24dp"
        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);
        }
    }
}