Android 以编程方式添加的 ConstraintLayout 未显示在屏幕上答案

【问题标题】：Android programmatically added ConstraintLayout isn't shown on screenAndroid 以编程方式添加的 ConstraintLayout 未显示在屏幕上
【发布时间】：2020-02-09 19:30:41
【问题描述】：

我正在尝试创建一个系统的布局绘制，它与表格非常相似，因此，我尝试创建一个包含行和列的约束布局（我可能需要用线连接，因此，垂直/horizontal 布局不是最适合它）。

另外，由于系统大小不同，只有在运行时才知道，所以我必须以编程方式绘制布局。

我在构造这样的 ConstraintLayout 时遇到了问题 - 即使我已将所有元素添加到布局中，它也不会在屏幕上呈现它们。

我正在使用带有 Java 8 的 Android Pie（API 级别 28，为使用它的非常特定的设备创建它）。

我已按照以下文章中的说明进行操作：

附加我的代码的简化版本（仍然不起作用）。

代码执行以下操作：

创建一些模型数据
对于每一行：

2.1。根据行中的数字创建按钮并将其添加到 general 布局

2.2。使用 general ConstrainSet
连接按钮
2.3。用当前行中的按钮创建一个链（因为我希望它们处于相同的高度）

2.4。将按钮编号 0 连接到上一行（或连接到屏幕顶部，这些是每行的“中心”）

代码是：

public class MainActivity extends AppCompatActivity {
    private final static String logTag = "Main Test";
    private final static int    NUM_OF_ROWS = 5;

    private List<List<Integer>> mLayoutNums;
    private ConstraintLayout mScreenLayout;

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

        mScreenLayout = findViewById(R.id.main_layout);

        createMockupData();

        drawBuildingLayout();
    }

    private void createMockupData() {
        mLayoutNums = new ArrayList<>(NUM_OF_ROWS);
        /*
            The output should be as follows:

            [2, 0, 1, 3]
               [0]
               [0, 1]
            [1, 0, 2, 3, 4]
               [0, 1, 2]
         */
        mLayoutNums.add(Arrays.asList(0, 1, 2));
        mLayoutNums.add(Arrays.asList(1, 0, 2, 3, 4));
        mLayoutNums.add(Arrays.asList(0, 1));
        mLayoutNums.add(Arrays.asList(0));
        mLayoutNums.add(Arrays.asList(2, 0, 1, 3));
    }

    private void drawBuildingLayout() {
        ConstraintSet conSet = new ConstraintSet();
        conSet.clone(mScreenLayout);

        int[] centerIds = new int[NUM_OF_ROWS];

        for (int row = NUM_OF_ROWS - 1; row >= 0; --row) {
            List<Integer> numsInRow = mLayoutNums.get(row);
            addSingleRow(row, numsInRow, conSet, centerIds);
        }

        // connect last row to the bottom
        conSet.connect(ConstraintSet.PARENT_ID,
                       ConstraintSet.BOTTOM,
                       centerIds[0],
                       ConstraintSet.BOTTOM);

        conSet.createVerticalChain(ConstraintSet.PARENT_ID,
                                   ConstraintSet.TOP,
                                   ConstraintSet.PARENT_ID,
                                   ConstraintSet.BOTTOM,
                                   centerIds,
                                   null,
                                   ConstraintSet.CHAIN_SPREAD);

        conSet.applyTo(mScreenLayout);
        Log.i(logTag, "the screen should be shown now: " + mScreenLayout.isShown());
    }

    private void addSingleRow(int row,
                              List<Integer> numsInRow,
                              ConstraintSet conSet,
                              int[] centerIds) {
        if (numsInRow.size() > 1) {
            addMultipleNumsRow(row, numsInRow, conSet, centerIds);
        }
        else if (numsInRow.size() == 1){
            addSingleNumRow(row, numsInRow.get(0), conSet, centerIds);
        }
    }

    private void connectToPrevRow(int row, ConstraintSet conSet, int[] centerIds) {
        if (row < NUM_OF_ROWS - 1) {
            conSet.connect(centerIds[row + 1],
                           ConstraintSet.BOTTOM,
                           centerIds[row],
                           ConstraintSet.TOP);
        } else if (row == NUM_OF_ROWS - 1) {
            conSet.connect(ConstraintSet.PARENT_ID,
                           ConstraintSet.TOP,
                           centerIds[row],
                           ConstraintSet.TOP);
        }
    }

    private void connectAndChainRow(int[] rowButtonIds,
                                    ConstraintSet conSet) {
        // First button will be attached to the left side of the parent
        int leftNeighborId = ConstraintSet.PARENT_ID;
        int leftNeighborSide = ConstraintSet.LEFT;

        for (int col = 0; col < rowButtonIds.length; ++col) {
            conSet.connect(leftNeighborId,
                           leftNeighborSide,
                           rowButtonIds[col],
                           ConstraintSet.LEFT);

            leftNeighborId = rowButtonIds[col];
            leftNeighborSide = ConstraintSet.RIGHT;
        }

        // Connecting to the right side of the parent
        conSet.connect(leftNeighborId,
                       leftNeighborSide,
                       ConstraintSet.PARENT_ID,
                       ConstraintSet.RIGHT);

        conSet.createHorizontalChain(ConstraintSet.PARENT_ID,
                                     ConstraintSet.LEFT,
                                     ConstraintSet.PARENT_ID,
                                     ConstraintSet.RIGHT,
                                     rowButtonIds,
                                     null,
                                     ConstraintSet.CHAIN_SPREAD);
    }

    private void addMultipleNumsRow(int row,
                                    List<Integer> numsInRow,
                                    ConstraintSet conSet,
                                    int[] centerIds) {
        int[] buttonsIds = new int[numsInRow.size()];

        for (int pos = 0; pos < numsInRow.size(); ++pos) {
            int col = numsInRow.get(pos);
            Button button = createButton(row, col);

            button.setLayoutParams(new ConstraintLayout.LayoutParams(ConstraintLayout.LayoutParams.WRAP_CONTENT,
                                                                                ConstraintLayout.LayoutParams.WRAP_CONTENT));

            int currButtonId = button.getId();
            buttonsIds[pos] = currButtonId;
            mScreenLayout.addView(button);

            if (pos == 0) {
                centerIds[row] = currButtonId;
            }
        }

        connectAndChainRow(buttonsIds, conSet);

        connectToPrevRow(row, conSet, centerIds);

        Log.i(logTag, "Created constrain chain and buttons for row: "
                      + row + " number of columns: "
                      + numsInRow.size());
    }

    private void addSingleNumRow(int row,
                                 int num,
                                 ConstraintSet conSet,
                                 int[] centerIds) {
        Button button = createButton(row, num);
        button.setLayoutParams(new ConstraintLayout.LayoutParams(ConstraintLayout.LayoutParams.WRAP_CONTENT,
                                                                        ConstraintLayout.LayoutParams.WRAP_CONTENT));

        mScreenLayout.addView(button);

        centerIds[row] = button.getId();

        conSet.connect(button.getId(), ConstraintSet.LEFT, ConstraintSet.PARENT_ID, ConstraintSet.LEFT);
        conSet.connect(button.getId(), ConstraintSet.RIGHT, ConstraintSet.PARENT_ID, ConstraintSet.RIGHT);

        connectToPrevRow(row, conSet, centerIds);
    }

    private Button createButton(int row, int col) {
        Button resButton = new Button(this);

        resButton.setTextAlignment(Button.TEXT_ALIGNMENT_CENTER);
        resButton.setText(String.format("(%d, %d)", row, col));

        resButton.setId(View.generateViewId());

        return resButton;
    }
}

【问题讨论】：

标签： android android-constraintlayout android-9.0-pie programmatically

【解决方案1】：

在添加视图之前，您正在克隆 ConstraintSet。结果，视图 id 不出现在 ConstraintSet 中，无法连接。

尝试将以下行移到 for 循环之后。

conSet.clone(mScreenLayout);

这可能无法解决所有问题，但可以帮助您入门。

顺便说一句，如果您还不知道，“布局检查器”（工具->布局检查器）是从模拟器或设备查看布局的好方法。

【讨论】：

【解决方案2】：

我在代码中发现了一些问题。

首先是Cheticamp 指出的错误。我只需要调用 ConstraintSet.clone() 函数在我已经将 all 的按钮添加到布局中。

但是，在我更改顺序后，我仍然将所有按钮排成一行，位于屏幕顶部。为了解决这个问题，我必须为所有按钮添加另一个约束 - 对于行 R 中的每个按钮，将 bottom 连接到 bottom 在该行中的中心按钮，因此所有将在同一行中对齐。

这解决了我在这段代码中的主要问题！

这是我的完整工作代码（供其他人参考，如果需要）：

public class MainActivity extends AppCompatActivity {
    private final static String logTag = "Main Test";
    private final static int    NUM_OF_ROWS = 5;

    private List<List<Integer>> mLayoutNums;
    private int[][]             mButtonIds;
    private ConstraintLayout    mScreenLayout;

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

        mScreenLayout = findViewById(R.id.main_layout);

        mButtonIds = new int[NUM_OF_ROWS][];

        createMockupData();

        drawBuildingLayout();
    }

    private void createMockupData() {
        mLayoutNums = new ArrayList<>(NUM_OF_ROWS);
        /*
            The output should be as follows:

            [2, 0, 1, 3]
               [0]
               [0, 1]
            [1, 0, 2, 3, 4]
               [0, 1, 2]

            Total: 15 stations
         */
        mLayoutNums.add(Arrays.asList(0, 1, 2));
        mLayoutNums.add(Arrays.asList(1, 0, 2, 3, 4));
        mLayoutNums.add(Arrays.asList(0, 1));
        mLayoutNums.add(Arrays.asList(0));
        mLayoutNums.add(Arrays.asList(2, 0, 1, 3));
    }

    private void drawBuildingLayout() {
        ConstraintSet conSet = new ConstraintSet();


        int[] centerIds = new int[NUM_OF_ROWS];

        for (int row = NUM_OF_ROWS - 1; row >= 0; --row) {
            List<Integer> numsInRow = mLayoutNums.get(row);
            addSingleRow(row, numsInRow, centerIds);
        }

        conSet.clone(mScreenLayout);

        for (int row = 0; row < NUM_OF_ROWS; ++row) {
            if (mButtonIds[row].length > 1) {
                connectAndChainRow(mButtonIds[row], centerIds[row], conSet);
            } else {
                conSet.centerHorizontally(centerIds[row], ConstraintSet.PARENT_ID);
            }
        }

        connectRows(conSet, centerIds);

        conSet.createVerticalChain(ConstraintSet.PARENT_ID,
                                   ConstraintSet.TOP,
                                   ConstraintSet.PARENT_ID,
                                   ConstraintSet.BOTTOM,
                                   centerIds,
                                   null,
                                   ConstraintSet.CHAIN_SPREAD);

        conSet.applyTo(mScreenLayout);
        Log.i(logTag, "the screen should be shown now: " + mScreenLayout.isShown());
    }

    private void addSingleRow(int row,
                              List<Integer> numsInRow,
                              int[] centerIds) {
        if (numsInRow.size() > 1) {
            addMultipleNumsRow(row, numsInRow, centerIds);
        }
        else if (numsInRow.size() == 1){
            addSingleNumRow(row, numsInRow.get(0), centerIds);
        }
    }

    private void connectRows(ConstraintSet conSet, int[] centerIds) {
        conSet.connect(ConstraintSet.PARENT_ID,
                       ConstraintSet.BOTTOM,
                       centerIds[0],
                       ConstraintSet.BOTTOM);

        for (int row = 0; row < NUM_OF_ROWS - 1; ++row) {
                conSet.connect(centerIds[row],
                               ConstraintSet.TOP,
                               centerIds[row + 1],
                               ConstraintSet.BOTTOM);
            }

        conSet.connect(centerIds[NUM_OF_ROWS - 1],
                       ConstraintSet.TOP,
                       ConstraintSet.PARENT_ID,
                       ConstraintSet.TOP);
    }

    private void connectAndChainRow(int[] rowButtonIds,
                                    int centerId,
                                    ConstraintSet conSet) {
        // First button will be attached to the left side of the parent
        conSet.connect(ConstraintSet.PARENT_ID,
                       ConstraintSet.LEFT,
                       rowButtonIds[0],
                       ConstraintSet.LEFT);

        for (int col = 0; col < rowButtonIds.length - 1; ++col) {
            conSet.connect(rowButtonIds[col],
                           ConstraintSet.RIGHT,
                           rowButtonIds[col + 1],
                           ConstraintSet.LEFT);

            if (rowButtonIds[col] != centerId) {
                conSet.connect(rowButtonIds[col],
                               ConstraintSet.BOTTOM,
                               centerId,
                               ConstraintSet.BOTTOM);
            }
        }

        if (rowButtonIds[rowButtonIds.length - 1] != centerId) {
            conSet.connect(rowButtonIds[rowButtonIds.length - 1],
                           ConstraintSet.BOTTOM,
                           centerId,
                           ConstraintSet.BOTTOM);
        }

        // Connecting to the right side of the parent
        conSet.connect(rowButtonIds[rowButtonIds.length - 1],
                       ConstraintSet.RIGHT,
                       ConstraintSet.PARENT_ID,
                       ConstraintSet.RIGHT);

        conSet.createHorizontalChain(ConstraintSet.PARENT_ID,
                                     ConstraintSet.LEFT,
                                     ConstraintSet.PARENT_ID,
                                     ConstraintSet.RIGHT,
                                     rowButtonIds,
                                     null,
                                     ConstraintSet.CHAIN_SPREAD);
    }

    private void addMultipleNumsRow(int row,
                                    List<Integer> numsInRow,
                                    int[] centerIds) {
        mButtonIds[row] = new int[numsInRow.size()];

        for (int pos = 0; pos < numsInRow.size(); ++pos) {
            int col = numsInRow.get(pos);
            Button button = createButton(row, col);

            button.setLayoutParams(new ConstraintLayout.LayoutParams(ConstraintLayout.LayoutParams.WRAP_CONTENT,
                                                                     ConstraintLayout.LayoutParams.WRAP_CONTENT));

            int currButtonId = button.getId();
            mButtonIds[row][pos] = currButtonId;
            mScreenLayout.addView(button);

            if (pos == 0) {
                centerIds[row] = currButtonId;
            }
        }

        Log.i(logTag, "Created constrain chain and buttons for row: "
                      + row + " number of columns: "
                      + numsInRow.size());
    }

    private void addSingleNumRow(int row,
                                 int num,
                                 int[] centerIds) {
        Button button = createButton(row, num);
        button.setLayoutParams(new ConstraintLayout.LayoutParams(ConstraintLayout.LayoutParams.WRAP_CONTENT,
                                                                 ConstraintLayout.LayoutParams.WRAP_CONTENT));

        mScreenLayout.addView(button);

        mButtonIds[row] = new int[1];
        mButtonIds[row][0] = button.getId();

        centerIds[row] = button.getId();
    }

    private Button createButton(int row, int col) {
        Button resButton = new Button(this);

        resButton.setTextAlignment(Button.TEXT_ALIGNMENT_CENTER);
        resButton.setText(String.format("(%d, %d)", row, col));

        resButton.setId(View.generateViewId());

        return resButton;
    }
}

【讨论】：